technical guidance document l conservation of fuel and

Building Regulations 2002

Technical Guidance Document L

Conservation of Fuel and EnergyDWELLINGS

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Amendments issued since publicationTechnical Guidance Document L - Conservation of

Fuel and Energy-Dwellings (2002)

Table 29: Note 7th line amended to read:-

“where N = 0.038F - 0.00005F2 (for F ≤ 300 m3)

L(vii)

Dwelling - Assessment of Compliance on Basis of HeatEnergy Rating Standard Calculation Worksheet

“Total Basic Air Change Rate should read:(32)+(33)+(34) = (35)

L(vi)

Table 20: bottom section amended to read:-

This table is derived for walls as in W3(a) above, exceptwith 100 mm of insulation (λ = 0.04) between 100 mmstuds and additional layer of insulation as specified in theTable across the studs

L(v)

“Provision of adequate roof space ventilation” replace theWord “Ventilation” with “Condensation”

L(iv)

Table 6: Heading in the first column to read:-

“Total thickness of insulation (mm)”

L(iii)

Table 2: Note 1 amended to read:-

NOTE 1: Intermediate values of “combined areas” or of“U-values” may be estimated by interpolation in theabove Table. Alternatively the following expression maybe used to calculate the appropriate values: Aope /Af =0.4825/(Uope – 0.27). This expression may also be used tocalculate appropriate values outside the range covered bythe table.

L(ii)

Table 2: Heading over Column 2 amended to read:-

Maximum combined area of external doors, windows and roof lights (Aope) as % of floor area (Af)

L(i)

Text AffectedAmd. No.

Example E1 - Heat Energy Rating Calculation: - Amendedto read:

“Base Temperature (K) (77) – (76) 12.85 (78)

L(xvi)


“Gains / Loss Ratio (72) / (50) 5.50 (73)

L(xv)


“Total Gains (68) + (71) = 1005.22 (72)

L(xiv)


“Total Other Gains (69) + (70) = 650.72 (71)

L(xiii)


“Gross Air Change Rate (35) + (43) = 0.98 (44)

L(xii)

Example E1: Semi-Detached House: Door and WindowOpenings: Amended to read:

(Including 1.8 m2 rear door)

L(xi)

Table 33: Note 2: 3rd, 4th, 5th lines amended to read:

10W, 10W 25W respectively.

L(x)

Table 33: Note 1: 4th line amended to read:

“N = 0.038F - 0.00005F2 (for F ≤ 300m3)

L(ix)

Solar and Other Energy Gains; Paragraph C.17 “Table 33”Amended to read:-

“Table 32”

L(viii)


© Government of Ireland 2005

“All Table numbers corrected (other than Tables 1 - 4),including references to Tables in the text”.

L(xxii)

Standards and Other References: Other Publications referred to:-

Architectural Heritage Protection Guidelines for PlanningAuthorities, Department of the Environment, Heritageand Local Government 2004.

L(xxi)

Standards and Other References: Other Publications referred to:-

Homebond : “Right on Site” Issue No. 28, BuildingRegulations 2002 - Conservation of Fuel and Energy -Dwellings 2002

L(xx)

Section 3: Insulation of Hot Water Storage Vessels, Pipesand Ducts: Paragraph 3.4 - Amended to read:......to the standard outlined in Paragraph 3.3 above,.......

L(xviii)

Standards and Other References I.S. EN ISO 10211-2:2001 Thermal bridge in building construction - heat flows and surface temperature. Part 2linear thermal bridges

L(xix)


“Energy to meet Space Heat Demand 0.024 x (79) x (50)= kWh/yr

5931.11 (80)

L(xvii)


1

Contents

1

Page

Introduction 2

Transitional Arrangements 2The Guidance 2Existing Buildings 2Technical Specifications 2Materials and Workmanship 3Interpretation 3

Part L - The Requirement 4

General Guidance 4Technical Risks and Precautions 5

General 5Fire Safety 5Ventilation 5

Thermal Conductivity and Thermal Transmittance 5Dimensions 6Application to Buildings of Architectural or Historic Interest 7

SECTION 1: LIMITATION OF HEAT LOSS THROUGH THE BUILDING FABRIC 8

General 8Elemental heat loss 8Overall heat loss 10Heat energy Rating 11Thermal Bridging 12Air Infiltration 14

SECTION 2: CONTROLS FOR SPACE HEATING AND HOT WATER SUPPLY SYSTEMS 15

SECTION 3: INSULATION OF HOT WATER STORAGE VESSELS, PIPES AND DUCTS 17

AppendicesA Calculation of U-values 19B Fabric Insulation: Additional Guidance for Common

Constructions including Tables of U-values 28C Heat Energy Rating: Standard Calculation Method 49D Thermal Bridging 61E Limitation of Heat Loss through Building Fabric 63

STANDARDS AND OTHER REFERENCES 68

2

IntroductionThis document has been published by the Ministerfor the Environment and Local Government underarticle 7 of the Building Regulations 1997. It providesguidance in relation to Part L of the Second Scheduleto the Regulations insofar as it relates todwellings . The document should be read inconjunction with the Building Regulations 1997, andother documents published under these Regulations.

In general, Building Regulations apply to theconstruction of new buildings and to extensions andmaterial alterations to buildings. In addition, certainparts of the Regulations apply to existing buildingswhere a material change of use takes place.Otherwise, Building Regulations do not apply tobuildings constructed prior to 1 June, 1992.

Pending updating Part L insofar as it relates tobuildings other than dwellings, guidance inrelation to those buildings can be found inBuilding Regulations 1997, Technical GuidanceDocument L

Transitional ArrangementsIn general, this document applies to works, orbuildings in which a material change of use takesplace, where the work or the change of usecommences or takes place, as the case may be, on orafter 1 January 2003. Technical Guidance DocumentL - Conservation of Fuel and Energy, dated1997, insofar as it relates to dwellings, also ceases tohave effect from that date. However, the latterdocument may continue to be used in the case ofdwellings:-

- where the work or the change of usecommences or takes place, as the case may be,on or before 31 December 2002, or

- where planning approval or permission hasbeen applied for on or before 31 December2002, and substantial work has beencompleted by 31 December 2005, or a noticepursuant to Part 8 of the Planning andDevelopment Regulations 2001 has beenpublished on or before 31 December 2002,and substantial work has been completed by31 December 2005.

“Substantial work has been completed” meansthat the structure of the external walls has beenerected.

In the case of the replacement of external doors,windows or rooflights, this document will apply towork which takes place on or after 1 July 2003.

The GuidanceThe materials, methods of construction, standardsand other specifications (including technicalspecifications) which are referred to in thisdocument are those which are likely to be suitablefor the purposes of the Building Regulations (asamended). Where works are carried out inaccordance with the guidance in this document, thiswill, prima facie, indicate compliance with Part L ofthe Second Schedule to the Building Regulations.However, the adoption of an approach other thanthat outlined in the guidance is not precludedprovided that the relevant requirements of theRegulations are complied with. Those involved inthe design and construction of a building may berequired by the relevant building control authority toprovide such evidence as is necessary to establishthat the requirements of the Regulations are beingcomplied with.

Existing BuildingsIn the case of material alterations or change of use ofexisting buildings, the adoption without modificationof the guidance in this document may not, in allcircumstances, be appropriate. In particular, theadherence to guidance, including codes, standards ortechnical specifications intended for application tonew work may be unduly restrictive or impracticable.Buildings of architectural or historical interest areespecially likely to give rise to such circumstances. Inthese situations, alternative approaches based on theprinciples contained in the document may be morerelevant and should be considered.

Technical SpecificationsBuilding Regulations are made for specific purposes,e.g. to provide, in relation to buildings, for the health,safety and welfare of persons, the conservation ofenergy, and access for disabled persons. Technicalspecifications (including harmonised EuropeanStandards, European Technical Approvals, NationalStandards and Agrement Certificates) are relevant tothe extent that they relate to these considerations.Any reference to a technical specification is areference to so much of the specification as isrelevant in the context in which it arises. Technicalspecification may also address other aspects notcovered by the Regulations.

Building Regulations 2002Technical Guidance Document LConservation of Fuel and Energy - DWELLINGS

3

A reference to a technical specification is to thelatest edition (including any amendments,supplements or addenda) current at the date ofpublication of this Technical Guidance Document.However, if this version of the technical specificationis subsequently revised or updated by the issuingbody, the new version may be used as a source ofguidance provided that it continues to address therelevant requirements of the Regulations.

Materials and WorkmanshipUnder Part D of the Second Schedule to the BuildingRegulations, building work to which the regulationsapply must be carried out with proper materials andin a workmanlike manner. Guidance in relation tocompliance with Part D is contained in TechnicalGuidance Document D.

InterpretationIn this document, a reference to a section, paragraph,appendix or diagram is, unless otherwise stated, areference to a section, paragraph, appendix ordiagram, as the case may be, of this document. Areference to another Technical Guidance Documentis a reference to the latest edition of a documentpublished by the Department of the Environmentand Local Government under article 7 of the BuildingRegulations 1997. Diagrams are used in thisdocument to il lustrate particular aspects ofconstruction - they may not show all the details ofconstruction.

4

Conservation of Fuel and Energy - DWELLINGS

GENERAL GUIDANCE

0.1 The philosophy underlying Part L of the FirstSchedule to the Building Regulations is thatoccupants can achieve adequate levels of thermalcomfort while minimising the use of scarce energyresources. Buildings should be designed andconstructed to achieve this aim as far as ispracticable. This requires, as a minimum, theprovision of energy efficient measures which –

(a) limit the heat loss and, where appropriate,maximise the heat gains through the fabricof the building,

(b) control as appropriate the output of thespace heating and hot water systems;

and

(c) limit the heat loss from pipes, ducts andvessels used for the transport or storage ofheated water or air.

This Technical Guidance Document providesguidance on how to satisfy the requirement in thesethree areas for dwellings. The existing TechnicalGuidance Document “Building Regulations 1997,Technical Guidance Document – L, Conservation ofFuel and Energy” continues to apply to buildingsother than dwellings.

A range of issues related to performance assessment,calculation methods and applicability of Part L aredealt with initially in the following paragraphs.

0.2 Paragraph 1.4 and Appendix C of thisdocument present a system of energy rating as apossible method of demonstrating compliance ofnew housing with the energy conservationrequirements of the Building Regulations. The use ofthe system and the provision of standardisedinformation derived from it will be promoted by theDepartment of Communications Marine and NaturalResources and the Sustainable Energy Authority ofIreland with a view to increasing awareness of theimportance of energy efficiency in housing. Toencourage greater use of this system, the authoritywill update the user-friendly computer software,which it has previously made available. This willenable compliance with Part L to be assessed andfacilitate the provision of energy performanceinformation in relation to new housing in astandardised format. Such information may be usedfor marketing purposes or as a means of conveyingto potential owners or occupants the energyefficiency advantages of buildings, which comply withthe Building Regulations.

0.3 For small extensions, not exceeding 6.5m2 infloor area, reasonable provision for the conservationof fuel and energy can be considered to have been

Building Regulations - The Requirement

1. The requirements regarding conservation of fuel and energy are laid out in Part L of the Second Schedule tothe Building Regulations 1997 (S.I. No. 497 of 1997).

2. The Second Schedule in relation to works relating to dwellings, is amended to read as follows:

Conservation of fuel L1 A building shall be so designed and constructed as to secure, insofar asand energy is reasonably practicable, the conservation of fuel and energy. This

shall be achieved by –

(a) limiting the heat loss and, where appropriate, maximising theheat gains through the fabric of the building

(b) controlling, as appropriate, the output of the space heating andhot water systems; and

(c) limiting the heat loss from pipes, ducts and vessels used for thetransport or storage of heated water or air.

5

made if the new construction is similar to theexisting construction. Unheated ancillary areas suchas porches, garages and the like do not requirespecific provisions for the conservation of fuel andenergy.

0.4 Where the occupancy level or level ofheating required when in use cannot be establishedat construction stage, the building should be treatedas fully heated and the provisions of Part L appliedaccordingly. It should be noted that the provisions ofPart L apply where a material change of use occursand such a change of use may require specificconstruction measures to comply with Part L. Thesemeasures may prove more costly than if carried outat the time of initial construction.

0.5 In large complex buildings it may be sensibleto consider the provisions for conservation of fueland energy separately for the different parts of thebuilding in order to establish the measuresappropriate to each part.

TECHNICAL RISKS ANDPRECAUTIONS

General

0.6 The incorporation of additional thickness ofthermal insulation and other energy conservationmeasures can result in changes in traditionalconstruction practice. Care should be taken indesign and construction to ensure that these changesdo not increase the risk of certain types of problems,such as rain penetration and condensation. Someguidance on avoiding such increased risk is given inAppendix B of this document. General guidance onavoiding risks that may arise from the incorporationof energy conservation measures is contained in thepublication “Thermal insulation: avoiding risks;Building Research Establishment (Ref BR 262)”.Guidance in relation to particular issues andmethods of construction will be found in relevantstandards. Guidance on construction details iscontained in the publication “Limiting thermalbridging and air leakage; Robust construction detailsfor dwellings and smaller buildings” published by TheStationery Office, London. In addition, guidance onappropriate details for common domesticconstructions will be provided in the HomeBondpublication “Right on the Site No. 28” (to bepublished shortly).

The guidance given in these documents is notexhaustive and designers and builders may have wellestablished details using other materials that areequally suitable.

Fire Safety

0.7 Part B of the Second Schedule to theBuilding Regulations prescribes fire safetyrequirements. In designing and constructing buildingsto comply with Part L, these requirements must bemet and the guidance in relation to fire safety inTGD B should be fully taken into account. Inparticular, it is important to ensure that windows,which are required as secondary means of escape inaccordance with Section 1.5 of TGD B, comply withthe dimensional and other requirements for suchwindows as set out in paragraph. 1.5.6 of TGD B.

Ventilation

0.8 Part F of the Second Schedule to theBuilding Regulations prescribes ventilationrequirements both to meet the needs of theoccupants of the building and to prevent excessivecondensation in roofs and roofspaces. A new editionof Technical Guidance Document F is beingpublished, simultaneously with this edition of TGD Lwhich amends guidance in relation to ventilation ofbathrooms, kitchens and ulitity rooms of dwellingsso as to provide for mechanical extract ventilation orequivalent to these areas. The aim is to minimisethe risk of condensation, mould growth or otherindoor air quality problems.

In addition to following the guidance in TGD F,appropriate heating and ventilation regimes must beemployed in occupied dwellings. Advice for housepurchasers and occupants on these issues ispublished separately by both HomeBond and theSustainable Energy Authority of Ireland.

THERMAL CONDUCTIVITY ANDTHERMAL TRANSMITTANCE

0.9 Thermal conductivity (λ-value) relates to amaterial or substance, and is a measure of the rate atwhich heat passes through a uniform slab of unitthickness of that material or substance, when unittemperature difference is maintained between itsfaces. It is expressed in units of Watts per metre perdegree (W/mK).

6

Thermal transmittance (U-value) relates to a buildingcomponent or structure, and is a measure of therate at which heat passes through that component orstructure when unit temperature difference ismaintained between the ambient air temperatures oneach side. It is expressed in units of Watts persquare metre per degree of air temperaturedifference (W/m2K). In this Part, U-values specifiedas maximum elemental U-values, or used to deriveaverage U-values, relate to elements exposed directlyor indirectly to the outside air. This includes floorsdirectly in contact with the ground, suspendedground floors incorporating ventilated orunventilated voids, and elements exposed indirectlyvia unheated spaces. The U-value takes account ofthe effect of the ground, voids and unheated spaceon the rate of heat loss, where appropriate. Heatloss through elements that separate dwellings orother premises that can reasonably be assumed to beoccupied and heated, is considered to be negligible.Such elements do not need to meet any particularU-value nor should they be taken into account incalculation of the overall transmission heat loss.

0.10 U-values and λ-values are dependant on anumber of factors and, for particular materials,products or components, measured values, certifiedby an approved body or certified laboratory (seeTGD D), should be used, where available .Measurements of thermal conductivity should bemade in accordance with I.S. EN 12664, I.S. EN12667 or I.S. EN 12939 as appropriate.Measurements of thermal transmittance should bemade in accordance with I.S. EN ISO 8990, or, in thecase of windows and doors, I.S. EN ISO 12567-1.The phasing out of the use of HCFC as a blowingagent for foamed insulants will be completed byJanuary 2004. Certified λ-values for these materialsshould take account of the blowing agent actuallyused.

0.11 In the absence of certified measured values,values of thermal conductivity given in Table 5 ofAppendix A may be used. This Table contains l-values for some common building materials. Theseare primarily based on data contained in I.S. EN12524 or in CIBSE Guide A, Section A3. The valuesprovide a general indication of the thermalconductivity that may be expected for thesematerials. However, values for specific products maydiffer from these illustrative values. For thermalinsulation materials, or other products or materials

which contribute significantly to overall thermaltransmittance, certified test data should be used inpreference to the values given in Table 5.

0.12 In the absence of certified measured values,U-values may be derived by calculation. Methods ofcalculation are outlined in Appendix A, together withexamples of their use.

0.13 The procedure for the calculation of U-values of elements adjacent to unheated space(previously referred to as semi-exposed elements) isdescribed in I.S. EN ISO 6946 and I.S. EN ISO 13789.

• I.S. EN ISO 6946 gives a simplified procedure,where the unheated space is treated as if itwas an additional homogeneous layer.

• I .S. EN ISO 13789 gives more preciseprocedures for the calculation of heat transferfrom a building to the external environmentvia unheated spaces, and may be used when amore accurate result is required.

A simplified procedure which may be used for typicalsituations is given in Appendix A, paragraph A.4.1.

0.14 Appendix B contains Tables of indicative U-values for certain common constructions. These arederived using the calculation methods referred to inAppendix A, and may be used in place of calculatedor measured values, where appropriate. These Tablesprovide a simple way to establish the U-value for agiven amount of insulation. Alternatively they may beused to establish the amount of insulation needed toachieve a given U-value. The values in the Tables havebeen derived taking account of typical repeatedthermal bridging where appropriate. Where anelement incorporates a non-repeating thermalbridge, e.g. where the continuity of insulation isbroken or penetrated by material of reducedinsulating quality, the U-value derived from the Tableshould be adjusted to account for this thermalbridge. Table 28 in Appendix B contains indicative U-values for external doors, windows and rooflights.

DIMENSIONS

0.15 Linear measurements for the calculation ofwall, roof and floor areas and building volumesshould be taken between the finished internal facesof the appropriate external building elements and, in

7

the case of roofs, in the plane of the insulation.Linear measurements for the calculation of the areasof external door, window and rooflight and dooropenings should be taken between internal faces ofappropriate cills, lintels and reveals. “Volume" meansthe total volume enclosed by all enclosing elementsand includes the volume of non-usable spaces such asducts, stairwells and floor voids in intermediatefloors.

APPLICATION TO BUILDINGS OFARCHITECTURAL AND HISTORICINTEREST

0.16 Part L does not apply to works (includingextensions) to an existing building which is a“protected structure” or a “proposed protectedstructure” within the meaning of the Planning andDevelopment Act 2000 (No 30 of 2000).

Nevertheless, the application of this Part may poseparticular difficulties for habitable buildings which,although not protected structures or proposedprotected structure may be of architectural orhistorical interest. Works such as the replacement ofdoors, windows and rooflights, the provision ofinsulated dry lining and damp-proofing to walls andbasements, insulation to the underside of slating andprovision of roof vents and ducting of pipeworkcould all affect the character of the structure. Ingeneral, the type of works described above shouldbe carefully assessed for their material and visualimpact on the structure. Historic windows anddoors should be repaired rather than replaced, anddrylining and damp-proofing should not disrupt ordamage historic plasterwork or flagstones and shouldnot introduce further moisture into the structure.Roof insulation should be achieved without damageto slating (either during the works or from erosiondue to condensation) and obtrusive vents should notaffect the character of the roof. In specific cases,relaxation of the values proposed may be acceptableif it can be shown to be necessary in order topreserve the architectural integrity of the particularbuilding. For more guidance on appropriate measuressee “Architectural Heritage Protection - Guidelinesfor Planning Authorities”, have been published by theDepartment of the Environment, Heritage and LocalGovernment.

8

Section 1:Limitations of Heat Loss through the Building Fabric

1.1 GENERAL

1.1.1 Any one of the following three methods maybe used to demonstrate that an acceptable level oftransmission heat loss through the elementsbounding the heated building volume is achieved

(a) The Elemental Heat Loss method(Paragraph 1.2);

(b) The Overall Heat Loss method(Paragraph 1.3);

(c) The Heat Energy Rating method(Paragraph 1.4).

For each of the three methods, the guidanceregarding the limitation of thermal bridging(Paragraphs 1.5.1, 1.5.2 and 1.5.3) and ofuncontrolled air infiltration through the buildingfabric (Paragraph 1.6.1) should be followed.

Any part of a roof which has a pitch of 70˚ or moremay be treated as a wall for the purpose of assessingthe appropriate level of thermal transmission.Elements separating the building from spaces whichcan be reasonably assumed to be heated should notbe included (See paragraph 0.9). An example of theuse of each of the three methods are given inAppendix E.

1.1.2 When assessing transmission loss throughthe building fabric unheated ancilliary area shouldgenerally be considered as external to the insulatedfabric. Their effect may be allowed for using methodsspecified in I.S. EN 6946 or I.S. EN ISO 13789 (seeparagraph 0.13 and Appendix A). Unheated areaswhich are wholly or largely within the buildingstructure and are not subject to excessive air-infiltration or ventilation, e.g. stairwells, corridors inbuildings containing flats, may be considered aswithin the insulated fabric. In that case, if theexternal fabric of these areas is insulated to the levelspecified, no particular requirement for insulationbetween the heated and unheated areas would arise.

1.1.3 An attached conservatory-style sunspace orthe like should generally be treated as an integralpart of the dwelling. However, where

• clearly intended for occasional or seasonal use;

• separated from the adjacent spaces within thedwelling by walls, doors and other opaque orglazed elements; and

• unheated or, if provided with a heating facility,having provision for automatic temperature andon-off control independent of the heatingprovision in the main dwelling;

it may be treated as an extension to the maindwelling for the purposes of assessment forcompliance with the provisions of Part L (seeParagraphs 1.2.1 to 1.2.4 and Table 1 below). In thiscase, the main dwelling may be assessed separatelyfor compliance by any of the three methods givenbelow. The attached sunspace should be treated asan unheated space for the purposes of thisassessment and should also be assessed separately asif it were an extension to an existing dwelling (seeparagraph 1.2.3).

1.1.4 This Part of the Building Regulations appliesto the replacement of external doors, windows, orrooflights in an existing dwelling. The average U-value of replacement units should not exceed thevalue of 2.2 W/m2K set out in Table 1. In thiscontext, the repair or renewal of parts of individualelements, e.g. window glass, window casement sash,door leaf should be considered as repair and notreplacement.

1.2 ELEMENTAL HEAT LOSS

1.2.1 To demonstrate acceptable transmission heatloss by this method, maximum average U-values forindividual building elements should not exceed thoseset out in Table 1.

1.2.2 The combined area of external door,window and rooflight openings should not exceed25% of floor area, when the average U-value of suchopenings is 2.2 W/m2K. However, both thepermitted combined area of external door, windowand rooflight openings and the maximum average U-value of these elements may be varied as set out inTable 2. The area of openings should not be reducedbelow that required for adequate daylightingprovision. BS 8206: Part 2 gives advice on adequatedaylight provision.

9

1.2.3 In applying paragraph 1.2.2 to an extensionto an existing dwelling, the relevant floor area maybe taken to be:

(a) the combined floor area of the existingdwelling and extension; in this case thecombined area of external doors, windowsand rooflight openings refers to the area ofsuch openings in the extended dwelling, i.e.the opening area of retained external doors,windows and rooflights together with theopening area of external doors, windows androoflights in the extension; or

(b) the floor area of the extension alone; in thiscase the combined area of external doors,window and rooflight openings refers to thearea of such openings in the extension alone.In assessing the maximum area of openingsallowed for any particular U-value, an areaequivalent to the area of external door,window and rooflight openings of the existingdwellings which have been closed or coveredover by the extension, can be added to thearea calculated in accordance with paragraph1.2.2 above.

For extensions which

• are separated from the adjacent spaces withinthe dwelling by walls, doors and other opaqueor glazed elements,

• are clearly intended for occasional or seasonaluse, and

• are unheated or, if provided with a heatingfacil ity, have provision for automatictemperature and on-off control independentof the heating provision in the existingdwelling.

The limitation on the combined area of exposedexternal door, window and rooflight openings doesnot apply. In this case the average U-value of theseelements should not exceed the value of 2.2 W/m2Kare set out in Table 1.

Fabric Elements New Buildings & Material AlterationsExtensions to to, or MaterialExisting Buildings Changes of Use of,

Existing Buildings

Pitched roof,insulationhorizontal atceiling level 0.16 0.35

Pitched roof,insulation on slope 0.20 0.35

Flat roof 0.22 0.35

Walls 0.27 0.60

Ground Floors 0.25

Other Exposed Floors 0.25 0.60

External doors,windowsand rooflights 2.201 2.20

NOTE 1: Permitted average U-value of external doors,windows and rooflights may vary as described in Paragraphs1.2.2 and 1.2.3, and Table 2

Table 1 Maximum average elemental U-value (W/m2K)

Average U-value of windows, Maximum combineddoors and rooflights (Uope) area of external doors,

(W/m2 K) windows and rooflights(Aope) as % of floor area (Af)

1.4 42.71.6 36.31.8 31.52.0 27.92.1 26.42.2 25.02.3 23.82.4 22.72.5 21.62.6 20.72.7 19.92.8 19.12.9 18.33.0 17.73.1 17.03.2 16.53.3 15.9

NOTE 1: Intermediate values of “combined areas” or of “U-values” may be estimated by interpolation in the aboveTable. Alternatively the following expression may be used tocalculate the appropriate value: Aope/Af = 0.4825/(Uope -

0.27). This expression may also be used to calculateappropriate values outside the range covered by the Table.

Table 2 Permitted variation in combinedareas and average U-values ofexternal doors, windows androoflights

10

1.2.4 There is a wide range of possible designs forexternal doors, windows and rooflights. Certified U-values should be used, where available. In theabsence of certified data, U-values should becalculated in accordance with I.S. EN ISO 10077-1 orI.S. EN ISO 10077-2, as appropriate (See AppendixA). Alternatively, the indicative U-values for thesecomponents given in Table 28 can be used (seeAppendix B).

1.2.5 Diagram 1 summarises the fabric insulationstandards and allowances applicable in the ElementalHeat Loss method.

1.1.3 OVERALL HEAT LOSS

1.3.1 This method sets a maximum acceptablelevel of transmission heat loss through the fabric of abuilding, in terms of the maximum average U-value(Um ) of all fabric elements contributing to heat loss.The level depends on the ratio of the total area ofthese elements (At) to the building volume (V), andis specified in Table 3. The acceptable level of heatloss is expressed graphically in Diagram 2.

1.3.2 In addition to achieving the maximumaverage value set, average elemental U-values shouldnot exceed the following:

roofs 0.25 W/m2Kwalls 0.37 W/m2Kground floors 0.37 W/m2K.

Area of Heat Loss Elements/ Maximum AverageBuilding Volume U Value (Um)

(At/V) (m-1 ) (W/m2K)

1.3 0.391.2 0.401.1 0.411.0 0.430.9 0.450.8 0.480.7 0.510.6 0.560.5 0.620.4 0.720.3 0.87

NOTE 1: The expression Um = 0.24 + 0.19 V/At can be

used to establish Um for intermediate values of At/V and for

values below 0.3m-1.

Table 3 Maximum average U-value (Um ) asa function of building volume (V)and fabric heat-loss area (At)

Diagram 1 Par. 1.2Summary of elemental U-values

0.22

0.272

0.272

AverageU-value2.21

NOTES

1. Windows, doors and rooflights should have maximum U-value of 2.2 W/m2K and maximum opening areaas set out in Table B3. However areas and U-values may be varied provided the total heat loss throughthese elements is not increased.

2. The U-value includes the effect of unheated voids or other spaces.

0.162

0.27

0.25

0.252

0.20

Unheated space

Unheatedattic

0.25

11

1.4 HEAT ENERGY RATING

1.4.1 The Heat Energy Rating (HER) of a dwellingis a measure of the annual energy output from theappliance or appliances that provide space and waterheating for the dwelling. The rating is calculated forstandardised room temperatures, levels of hot wateruse and conditions of operation by the methodspecified in Appendix C. This involves thecalculation of the energy required

(a) to offset transmission and air infiltrationheat losses through the building fabric,including losses associated with thermalbridging (See Section 1.5 below)

(b) to offset heat losses associated withventilation/air infiltration, and

(c) to provide for domestic hot water.

Solar gain and internal heat gains are taken intoaccount in the calculation as are the type of heatingsystem and its controls. The rating is specified interms of energy output of the appliance orappliances per unit floor area per year (kWh/m2/yr).

1.4.2 Subject to paragraph 1.4.3 below, compliance

with the requirements of Part L is demonstrated fordwellings when the calculated HER is less than theMaximum Permitted Heat Energy Rating (MPHER)specified in Table 4. This method allows sometradeoff between levels of insulation and othermeasures e.g. controlled air infi ltration andventilation, provision for solar gains, and space andwater heating system controls.

Area of Heat Loss Elements/ Maximum PermittedBuilding Volume Heat Energy Rating(At / V) (m-1) (MPHER) (kWh/m2/yr.)

1.25 102.51.2 101.41.1 99.21.0 99.00.9 94.80.8 92.60.7 90.40.6 88.20.5 86.00.4 83.80.3 81.6

NOTE 1: MPHER can be derived for intermediate values ofAt / V by interpolation in the above Table. Alternatively, itmay be calculated from the expression MPHER < 22At / V +75.

Table 4 Maximum Permitted Heat EnergyRating as a function of buildingvolume (V) and fabric heat-lossarea (At)

Diagram 2 Par. 1.3Maximum average U-value (Um) in relation to building volume (V) and total areaof heat loss elements (At)

1.5

1.0

0.5

0.39

00.8 1 2 3 4

V/At (m)

Um = 0.24 + 0.19 V/At(Subject to lower limit on requirement of Um = 0.39 W/m2K)

Um(W/m2K)

12

1.4.3 In addition to achieving the target MPHERvalue set in Table 4, average elemental U-valuesshould not exceed the following:

roofs 0.25 W/m2Kwalls 0.37 W/m2Kground floors 0.37 W/m2K

1.5 THERMAL BRIDGING

1.5.1 To avoid excessive heat losses and localcondensation problems, provision should be made tolimit local thermal bridging, e.g. around windows,doors and other wall openings, at junctions betweenelements and at other locations. Any thermal bridgeshould not pose a risk of surface or interstitialcondensation and any excessive increase in heat lossassociated with the thermal bridge should be takenaccount of in the calculation of average U-value.

Paragraph 1.5.2 and 1.5.3 give guidance onreasonable provision for the limitation of thermalbridging. As an alternative to following the guidancein these paragraphs (and associated referencedocuments) reasonable provision can be shown bycalculation. Appendix D gives information on thecalculation procedure which can be used for thispurpose.

1.5.2 Use of sill, jamb, lintel and junction details setout in the HomeBond publication “Right on the SiteNo. 28”, the publication “Limiting thermal bridgingand air leakage: Robust construction details fordwellings and smaller buildings” (published by TheStationery Office, London), or other publisheddetails which have been assessed as satisfying theguidance in relation to Temperature Factor andLinear Thermal Transmittance set out in AppendixD, should represent reasonable provision to limitthermal bridging.

Lintel, jamb and sill designs similar to those shown inDiagram 3 would be satisfactory and heat losses dueto thermal bridging can be ignored if they areadopted. At lintels, jambs and sills generally a 15 mmthickness of insulation material having λ value of 0.04W/mK (or equivalent) will generally be adequate.

1.5.3 Care should be taken to control the risk ofthermal bridging at the edges of floors. All slab-on-ground floors should be provided with edgeinsulation to the vertical edge of the slab at all

external and internal walls. The insulation shouldhave minimum thermal resistance of 0.7 m2 K/W(25 mm of insulation with thermal conductivity of0.035 W/mK, or equivalent). Some large floors mayhave an acceptable average U-value without the needfor added insulation. However, perimeter insulationshould always be provided. Perimeter insulationshould extend at least 0.5m vertically or 1mhorizontally. Where the perimeter insulation isplaced horizontally, insulation to the vertical edge ofthe slab should also be provided as indicated above.

13

Diagram 3 Par. 1.5Lintel, jamb and sill designs

LINTELS JAMBS

HEAT LOSS PATHSwithout insulation

INTERNAL INSULATION

PARTIAL CAVITY FILL

FULL CAVITY FILL

NOTE

1. The internal faces of metal lintels should be covered with at least 15 mm of lightweight plaster; alternatively they can be dry-lined.

SILLS

14

1.6 AIR INFILTRATION

1.6.1 Infiltration of cold outside air should belimited by reducing unintentional air paths as far as ispracticable. Measures to ensure this include:

(a) sealing the void between dry-lining andmasonry walls at the edges of openings suchas windows and doors, and at the junctionswith walls, floors and ceilings (e.g. bycontinuous bands of bonding plaster orbattens),

(b) sealing vapour control membranes intimber-frame constructions,

(c) fitting draught-stripping in the frames ofopenable elements of windows, doors androoflights,

(d) sealing around loft hatches,

(e) ensuring boxing for concealed services issealed at floor and ceiling levels and sealingpiped services where they penetrate orproject into hollow constructions or voids.

Diagram 4 illustrates some of these measures.

Care should be taken to ensure compliance with theventilation requirements of Part F and Part J.

Diagram 4 Par. 1.6Air infiltration measures

Continuous seals(bonding plaster,battens or similar)

Seal at perimeter

Draught seal

Draught sealBolt or catch to compressdraught seal

Close fittinghole inplasterboard

Seals Ceiling

1. POSITION OF CONTINUOUS SEALING BANDS FOR DRY-LININGS FIXED TO MASONRY WALLS

2. SEALING AT WINDOWS AND DOORS

3. SEALING OF LOFT HATCH

4. SEALING AROUND SERVICE PIPES

15

Section 2:Controls for Space Heating and Hot Water Supply System

2.1 Space and water heating systems should beeffectively controlled so as to ensure the efficient useof energy by limiting the provision of heat energy useto that required to satisfy user requirements, insofaras reasonably practicable. The aim should be toprovide the following minimum level of control:

• automatic control of space heating on basisof room temperature;

• automatic control of heat input to stored hotwater on basis of stored water temperature;

• separate and independent automatic timecontrol of space heating and hot water;

• shut down of boiler or other heat sourcewhen there is no demand for either space orwater heating from that source.

The guidance in Paragraphs 2.2 to 2.5 below isspecifically applicable to fully pumped hot water-based central heating systems. Where practicable, anequivalent level of control should be achieved withother systems, having due regard to requirements toensure safety in use. For solid fuel fired systems, inparticular, the control system should be such as toallow safe operation of the boiler at its minimumburning rate, and to provide for the slumber load ofthe boiler through uncontrolled circulation to aradiator or hot water storage cylinder, or by otherappropriate mechanism.

2.2 Provision should be made to control heatinput on the basis of room temperature, e.g. by theuse of room thermostats, thermostatic radiatorvalves or other equivalent form of sensing device.Independent temperature control should generallybe provided for separate zones that normallyoperate at different temperatures, e.g. living andsleeping zones. Depending on the design and layoutof the dwelling, control on the basis of a single zonewill generally be satisfactory for smaller dwellings.Where the dwelling floor area exceeds 100 m2,control on the basis of two independent zones willgenerally be appropriate. In certain cases additionalzone control may be desirable, e.g. zones whichexperience significant solar or other energy inputsmay be controlled separately from zones notexperiencing such inputs.

2.3 Hot water storage vessels should be fittedwith thermostatic control that shuts off the supply ofheat when the desired storage temperature isreached.

2.4 Separate and independent time control forspace heating and for heating of stored water shouldbe provided. Independent time control of spaceheating zones may be appropriate whereindependent temperature control applies, but is notgenerally necessary.

2.5 The operation of controls should be suchthat the boiler is switched off when no heat isrequired for either space or water heating. Systemscontrolled by thermostatic radiator valves should befitted with flow control or other equivalent device toprevent unnecessary boiler cycling.

2.6 Alternative methods of meeting therequirement would be to adopt, as appropriate, therelevant recommendations in the following standardsprovided the measures adopted include similarzoning, timing, anti-cycling and boiler controlfeatures:

• BS 5449: 1990 Specification for forcedcirculation hot water central heating systemsfor domestic purposes;

• BS 5864: 1989 Specification for installation indomestic premises of gas-fired ducted air-heaters of rated output not exceeding 60kW.

16

Diagram 5 Para. 2.1Controls for space and water heating in dwellings

Hot watertemperaturecontrol

Time control:separate controlfor space and waterheating

Space heating temperature control byroom thermostat, thermostatic radiatorvalves or equivalent.

Separate time and temperature controlin two or more zones where floor areais greater than 100 m2

Controls switch off boilerwhen there is no demandfor space or water heating

NOTES:

1. For dwellings heated other than by central heating boiler, a similar level of control should be achieved.

2. For solid fuel fired systems, sufficient permanent heat load to satisfy slumber conditions must be maintained

Circulatingpump

17

Section 3:Insulation of Hot Water Storage Vessels , Pipes and Ducts

3.1 All hot water storage vessels, pipes andducts associated with the provision of heating andhot water in a dwelling should be insulated toprevent heat loss except for hot water pipes andducts within the normally heated area of the dwellingwhich contribute to the heat requirement of thedwelling.

3.2 Adequate insulation of hot water storagevessels can be achieved by the use of a storage vesselwith factory-applied insulation of such characteristicsthat, when tested on a 120 litre cylinder complyingwith I.S. 161:1975 using the method specified in BS1566, Part 1, Appendix B, standing heat losses arerestricted to 1W/litre. Use of a storage vessel with35 mm, factory-applied coating of PU-foam havingzero ozone depletion potential and a minimumdensity of 30 kg/m3 satisfies this criterion (seeDiagram 6). Alternative insulation measures givingequivalent performance may also be used.

3.3 Unless the heat loss from a pipe or ductcarrying hot water contributes to the useful heatrequirement of a room or space, the pipe or ductshould be insulated. The following levels of insulationshould suffice (see diagrams 6 and 7):

• pipe or duct insulation meeting therecommendations of BS 5422: 2001 Methodsof specifying thermal insulating materials forpipes, ductwork and equipment (in thetemperature range -400C to + 700C), or

• for pipes up to 40 mm diameter, insulationwith material of such thickness as gives anequivalent reduction in heat loss as thatachieved using material having a thermalconductivity at 400C of 0.035 W/mK and athickness equal to the outside diameter ofthe pipe, for pipes up to 40 mm diameter,and a minimum of 40 mm for larger pipes.

3.4 The hot pipes connected to hot waterstorage vessels, including the vent pipe and theprimary flow and return to the heat exchanger,where fitted, should be insulated, to the standardoutlined in Paragraph 3.3 above, for at least onemetre from their point of connection or up to thepoint where they are concealed.

Diagram 6 Para. 1.3.1

Insulation of hot water storage vessels and pipes

Provide

(a) factory applied insulationor

(b) alternative meeting requirementsspecified in Para. 1.3.2

Heating and hot water pipes inunheated space:

Provide thermal insulation

(a) with thermal conductivity of not greater than 0.035 W/mK and minimum thickness of pipeoutside diameter or 40 mm whichever is the lesser, or,

(b) to BS 5422: 2001

Hot pipes connectingto hot water storage:Insulate for 1 m fromconnection or up towhere concealed.Use 15 mminsulation thermalconductivity 0.035W/mK or equivalent

HOT

WATER

STORAGE

18

3.5 It should be noted that water pipes andstorage vessels in unheated areas will generally needto be insulated for the purpose of protection againstfreezing. Guidance on suitable protection measures isgiven in BRE Report 262, Thermal insulation:avoiding risks.

Diagram 7 Para. 3.3Insulation of warm air ducts

Heater

Warm airduct inunheatedspace

Provide thermalinsulation to BS 5422: 2001

19

GENERAL

A1.1 For building elements and componentsgenerally, the method of calculating U-values, isspecified in I.S. EN ISO 6946. U-values ofcomponents involving heat transfer to the ground,e.g. ground floors with or without floor voids,basement walls, are calculated by the methodspecified in I.S. EN ISO 13370. U-values for windows,doors and shutters may be calculated using I.S. ENISO 10077-1 or I.S. EN ISO 10077-2. A method forassessing U-values of light steel-framed constructionsis given in BRE Digest 465. General Guidance on theCalculation of U-values is contained in BR 443“Conventions for the Calculation of U-values”.Information on U-values and guidance on calculationprocedures contained in the 1999 edition of CIBSEGuide A3: Thermal Properties of Building Structuresare based on these standards and may be used toshow compliance with this Part. A soil thermalconductivity of 2.0 W/mK should be used, unlessotherwise verified.

A1.2 U-values derived by calculation should berounded to two significant figures and relevantinformation on input data should be provided. Whencalculating U-values the effects of timber joists,structural and other framing, mortar bedding,window frames and other small areas where thermalbridging occurs must be taken into account. Similarly,account must be taken of the effect of small areaswhere the insulation level is reduced significantlyrelative to the general level for the component orstructure element under consideration. Thermalbridging may be disregarded, however, where thegeneral thermal resistance does not exceed that inthe bridged area by more than 0.1 m2K/W. Forexample, normal mortar joints need not be takeninto account in calculations for brickwork orconcrete blockwork where the density of the brickor block material is in excess of 1500 kg/m3. Aventilation opening in a wall or roof (other than awindow, rooflight or door opening), and a metercupboard recess may be considered as having thesame U-value as the element in which it occurs.

A1.3 Examples of the application of the calculationmethod specified in I.S. EN 6946 are given below. Anexample of the calculation of ground floor U-valuesusing I.S. EN ISO 13370 is also given.

A1.4 Thermal conductivities of common buildingmaterials are given in Table 5. For the most part,these are taken from I.S. EN 12524: or CIBSE GuideA3.

SIMPLE STRUCTURE WITHOUTTHERMAL BRIDGING

A2.1 To calculate the U-value of a buildingelement (wall or roof) using I.S. EN ISO 6946, thethermal resistance of each component is calculated,and these thermal resistances, together with surfaceresistances as appropriate, are then combined toyield the total thermal resistance and U-value. Theresult is corrected to account for mechanical fixings(e.g. wall ties) or air gaps if required. For an elementconsisting of homogenous layers with no thermalbridging, the total resistance is simply the sum ofindividual thermal resistances and surface resistances.

Appendix A: Calculation of U-Values

20

Material Density Thermal(kg/m3) Conductivity

(W/mK)

General Building MaterialsClay Brickwork (outer leaf) 1,700 0.77Clay Brickwork (inner leaf) 1,700 0.56Concrete block (heavyweight) 2,000 1.33Concrete block (medium weight) 1,400 0.57Concrete block (autoclaved aerated) 600 0.18Cast concrete, high density 2,400 2.00Cast concrete, medium density 1,800 1.15Aerated concrete slab 500 0.16Concrete screed 1,200 0.41Reinforced concrete (1% steel) 2,300 2.30Reinforced concrete (2% steel) 2,400 2.50Wall ties, stainless steel 7,900 17.00Wall ties, galvanised steel 7,800 50.00Mortar (protected) 1,750 0.88Mortar (exposed) 1,750 0.94External rendering (cement sand) 1,300 0.57Plaster ( gypsum lightweight) 600 0.18Plaster (gypsum) 1,200 0.43Plasterboard 900 0.25

Natural Slate 2,500 2.20Concrete tiles 2,100 1.50Fibrous cement slates 1,800 0.45Ceramic tiles 2,300 1.30Plastic tiles 1,000 0.20Asphalt 2,100 0.70Felt bitumen layers 1,100 0.23

Timber, softwood 500 0.13Timber, hardwood 700 0.18Wood wool slab 500 0.10Wood-based panels (plywood, chipboard, etc.) 500 0.13

InsulationExpanded polystyrene (EPS) slab (HD) 25 0.035Expanded polystyrene (EPS) slab (SD) 15 0.037Extruded polystyrene 30 0.025Glass fibre / wool quilt 12 0.040Glass fibre / wool batt 25 0.035Phenolic foam 30 0.025Polyurethane board 30 0.025

Table 5 Thermal conductivity of some common building materials

NOTE: The values in this Table are indicative only. Certified values, taking ageing into account, where appropriate,should be used in preference, if available. This applies particularly to insulation materials.

21

Layer/Surface Thickness Conductivity Resistanc(m) (W/mK) (m2K/W)

External surface ----- ----- 0.040External render 0.019 0.57 0.033Concrete Block 0.100 1.33 0.075Air cavity ----- ----- 0.180Insulation 0.080 0.025 3.200Concrete Block 0.100 1.33 0.075Plaster (lightweight) 0.013 0.18 0.072Internal surface ----- ----- 0.130

Total Resistance ----- ----- 3.805

U-value of construction = 1/3.805 = 0.26 W/m2K

Example A1: Masonry cavity wall

I.S. EN 6946: provides for corrections to thecalculated U-value. For this construction, correctionsfor air gaps in the insulated layer and for mechanicalfasteners may apply. However, if the total correctionis less than 3% of the calculated value, the correctionmay be ignored.

In this case no correction for air gaps applies as it isassumed that the insulation boards meet thedimensional standards set out in I.S. EN ISO 6946and that they are installed without gaps greater than5 mm. The construction involves the use of wall tiesthat penetrate fully through the insulation layer.

A potential correction factor applies which, assumingthe use of 4 mm diameter stainless steel ties at 5 tiesper m2, is calculated as, 0.006 W/m2K. This is lessthan 3% of the calculated U-value and may beignored. It should be noted that, if galvanised steelwall ties were used, a correction of 0.02 W/m2Kwould apply, and the corrected U-value for thisconstruction would be 0.28 W/m2K.

STRUCTURE WITH BRIDGED LAYER(S)

A2.2 For an element in which one or more layersare thermally bridged, the total thermal resistance iscalculated in three steps as follows.

(a) the upper thermal resistance is based on theassumption that heat flows through thecomponent in straight lines perpendicular tothe element's surfaces. To calculate it, allpossible heat flow paths are identified, for eachpath the resistance of all layers are combinedin series to give the total resistance for thepath, and the resistances of all paths are thencombined in parallel to give the upperresistance of the element.

(b) the lower thermal resistance is based on theassumption that all planes parallel to thesurfaces of the component are isothermalsurfaces. To calculate it, the resistances of allcomponents of each thermally bridged layerare combined in parallel to give the effectiveresistance for the layer, and the resistances ofall layers are then combined in series to givethe lower resistance of the element.

(c) the total thermal resistance is the mean of theupper and lower resistances.

Diagram 8 Para. A.2.1Masonry Cavity wall

19mm external render

100mm dense concrete block outerleaf

Cavity (min 40 mm residual cavity)

80mm thermal insulation (thermalconductivity 0.025 W/mK)

90mm dense concrete block innerleaf

13mm lightweight plaster

HEAT FLOW

22

Example A2: Timber-frame wall (with oneinsulating layer bridged)

The thermal resistance of each component iscalculated (or, in the case of surface resistances,entered) as follows:

Upper resistanceAssuming that heat flows in straight l inesperpendicular to the wall surfaces, there are twoheat flow paths - through the insulation and throughthe studs. The resistance of each of these paths iscalculated as follows.

Resistance through section containing insulation [m2 K / W]:

External surface resistance 0.040Brick outer leaf 0.132Air cavity 0.180Sheathing ply 0.092Mineral wool insulation 3.750Plasterboard 0.052Internal surface resistance 0.130

Total 4.377

Resistance through section containing timber stud[m2 K / W]

External surface resistance 0.040Brick outer leaf 0.132Air cavity 0.180Sheathing ply 0.092Timber studs 1.154Plasterboard 0.052Internal surface resistance 0.130

Total 1.781

The upper thermal resistance Ru is obtained from:

Ru = 1 / (F1 / R1 + F2 / R2)

where F1 and F2 are the fractional areas of heat flowpaths 1 and 2, and R1 and R2 are the resistances ofthese paths.

Upper resistance Ru = 1 / (0.88 / 4.377 + 0.12 /1.781) = 3.725 m2 K / W

Lower resistanceAssuming an isothermal plane on each face of thelayer of insulation which is bridged by timber studs,the thermal resistance of this bridged layer, Rb, iscalculated from

Rb = 1 / (Fins / Rins + Ft / Rt)where Fins and Ft are the fractional areas of insulationand timber, and Rins and Rt are their resistances.

Rb = 1 / (0.88 / 3.750 + 0.12 / 1.154) = 2.953 m2 K / W

The resistances of all layers are then combined inseries to give the lower resistance [m2 K / W]

Layer/Surface Thickness Conductivity Resistanc

(m) (W/mK) (m2 K / W)

External surface --- --- 0.040

Brick outer leaf 0.102 0.77 0.132

Air cavity --- --- 0.180

Sheathing ply 0.012 0.13 0.092

Mineral wool insulation 0.150 0.04 3.750

Timber studs 0.150 0.13 1.154

Plasterboard 0.013 0.25 0.052

Internal surface --- --- 0.130

Diagram 9 Para. A.2.2Timber-frame wall

102mm brick outer leaf

Cavity

Sheathing ply

150mm insulating material betweenstuds (thermal conductivity 0.04W/mK)

Vapour control layer

13mm plasterboard

HEAT FLOW

23

External surface resistance 0.040Brick outer leaf 0.132Air cavity 0.180Bracing board 0.092Bridged insulation layer 2.953Plasterboard 0.052Internal surface resistance 0.130

Lower resistance (Rl) 3.580

Total resistance

The total resistance Rt is given by:

Rt = (Ru + Rl) / 2 = (3.725 + 3.580) / 2 = 3.652 m2 K / W

The U-value is the reciprocal of the total resistance:U-value = 1 / 3.652 = 0.27 W/m2K (to 2 decimalplaces).

There is a potential correction for air gaps in theinsulation layer. I.S. EN ISO 6946 gives a U-valuecorrection of 0.0065 W/m2K for this construction.This is less than 3% of the calculated U-value and canbe ignored.

Example A3: Domestic pitched roof withinsulation at ceiling level (between andover joists).

A pitched roof has 100 mm of mineral wool tightlyfitted between 44 mm by 100 mm timber joistsspaced 600 mm apart (centres to centres) and 150mm of mineral wool over the joists. The roof is tiledwith felt or boards under the tiles. The ceilingconsists of 13 mm of plasterboard. The fractionalarea of timber at ceiling level is taken as 8%.

Upper resistance (Ru)Resistance through section containing both layers ofinsulation [m2K/W]

External surface resistance 0.040Resistance of roof space 0.200Resistance of mineral wool over joists 3.750Resistance of mineral wool between joists 2.500

Resistance of plasterboard 0.052Inside surface resistance 0.100

Total 6.642

Diagram 10 Para. A.2.2 Domestic pitched roof

19mm tiles

35mm timber battens

2mm sarking felt

Rafters

250mm thermal insulation(thermal conductivity 0.04W/mK) with 100mm laidbetween timber ceiling joistsand 150mm over joists withvapour control layer, whereappropriate.

13mm plasterboard ceiling

HEAT FLOW

Ventilated roof space

Layer/Surface Thickness Conductivity Resistanc

(m) (W/mK) (m2K/W)

External surface - - 0.040

Roof space (including sloping

construction and roof cavity) - 0.200

Mineral wool (continuous layer) 0.150 0.04 3.750

Mineral wool (between joists) 0.100 0.04 2.500

Timber joists 0.100 0.13 1.154

Plasterboard 0.013 0.25 0.052

Internal surface - - 0.100

24

Resistance through section containing timber joists

External surface resistance 0.040Resistance of roof space 0.200Resistance of mineral wool over joists 3.750Resistance of timber joists 0.769Resistance of plasterboard 0.052Inside surface resistance 0.100

Total 4.911

The upper thermal resistance [Ru ] is obtained from:

Ru = 1 / (F1 / R1 + F2 / R2)

where F1 and F2 are the fractional areas of heat flowpaths 1 and 2, and R1 and R2 are the resistances ofthese paths.

Upper resistance Ru = 1 / (0.92 / 6.642 + 0.08 /4.911) = 6.460 m2 K/W

Lower resistance (Rl)

Assuming an isothermal plane on each face of thelayer of insulation which is bridged by timber studs,the thermal resistance of this bridged layer, Rb, iscalculated from

Rb = 1 / (Fins / Rins + Ft / Rt)

where Fins and Ft are the fractional areas of insulationand timber, and Rins and Rt are their resistances.

Rb = 1 / (0.92 / 2.500 + 0.08 / 0.769) = 2.119 m2K/W

The resistances of all layers are then combined inseries to give the lower resistance [m2K/W]

External surface resistance 0.040Resistance of roof space 0.200Resistance of mineral wool over joists 3.750Resistance of bridged layer 2.119Resistance of plasterboard 0.052Inside surface resistance 0.100

Lower resistance (Rl) 6.261

Total resistanceThe total resistance Rt is given by:Rt = (Ru + Rl) / 2 = (6.460 + 6.261) / 2 = 6.361m2K/W

The U-value is the reciprocal of the total resistance:

U-value = 1 / 6.361 = 0.16 W/m2K (to 2 decimalplaces).

I.S. EN ISO 6946: does not specify any potentialcorrection for this construction.

GROUND FLOORS AND BASEMENTS

A3.1 The U-value of an uninsulated ground floordepends on a number of factors including floor shapeand area and the nature of the soil beneath the floor.I.S. EN ISO 13370: deals with the calculation of U-values of ground floors. Methods are specified forfloors directly on the ground and for floors withvented and unvented sub-floor spaces. I.S. EN ISO13370: also covers heat loss from basement floorsand walls.

A3.2 In the case of semi-detached or terracedpremises, blocks of flats and similar buildings, thefloor dimensions can be taken as either those of theindividual premises or those of the whole building.When considering extensions to existing buildingsthe floor dimensions can be taken as those of theextension alone or those of the whole building.Unheated spaces outside the insulated fabric, such asattached porches or garages, should be excludedwhen deriving floor dimensions but the length of thefloor perimeter between the heated building and theunheated space should be included whendetermining the length of exposed perimeter.

A3.3 Slab-on-ground floors, with minimumprovision for edge insulation as specified in Paragraph1.5.3, achieve a U-value of 0.45 W/m2K withoutextra insulation provided the ratio of exposedperimeter length to floor area is less than 0.20. Inorder to achieve a U-value of 0.25 W/m2K this ratiomust be less than 0.10.

25

Example A4: Slab-on-ground floor – fullfloor insulation.

The slab-on-ground floor consists of a 150 mmdense concrete ground floor slab on 100 mminsulation. The insulation has a thermal conductivityof 0.035 W/mK. The floor dimensions are 8750 mmby 7250 mm with three sides exposed. One 8750mm side abuts the floor of an adjoining semi-detached house.

In accordance with I.S. EN ISO 13370, the followingexpression gives the U-value for well-insulated floors:

U = λ/(0.457B’ + dt), whereλ = thermal conductivity of

unfrozen ground (W/mK)B’ = 2A/P (m)dt = w + λ(Rsi + Rf + Rse) (m)A = floor area (m2)P = heat loss perimeter (m)w = wall thickness (m)

Rsi, Rf and Rse are internal surface resistance, floorconstruction (including insulation) resistance andexternal surface resistance respectively. Standardvalues of Rsi and Rse for floors are given as 0.17m2K/W and 0.04 m2K/W respectively. The standardalso states that the thermal resistance of denseconcrete slabs and thin floor coverings may be

ignored in the calculation and that the thermalconductivity of the ground should be taken as 2.0W/mK unless otherwise known or specified.

Ignoring the thermal resistance of the denseconcrete slab, the thermal resistance of the floorconstruction (Rf) is equal to the thermal resistanceof the insulation alone, i.e. 0.1/0.035 or 2.857m2K/W. Taking the wall thickness as 300 mm, thisgives

dt = 0.30 + 2.0(0.17 + 2.857 + 0.04) = 6.434 m.

Also B1 = 2(8.75 x 7.25) / (8.75 + 7.25 + 7.25) = 5.457 m

Therefore U = 2.0 / ((0.457 x 5.457) + 6.434) = 0.22 W/m2K.

The edge insulation to the slab is provided toprevent thermal bridging at the edge of the slab. I.S.EN ISO 13370 does not consider this edge insulationas contributing to the overall floor insulation andthus reducing the floor U-value. However, edgeinsulation, which extends below the external groundlevel, is considered to contribute to a reduction infloor U-value and a method of taking this intoaccount is included in the standard. Foundation wallsof insulating lightweight concrete may be taken asedge insulation for this purpose.

ELEMENTS ADJACENT TO UNHEATEDSPACES

A4.1 As indicated in paragraph 0.13, theprocedure for the calculation of U-values of elementsadjacent to unheated spaces (previously referred toas semi-exposed elements) is given in I.S. EN ISO6946 and I.S. EN ISO 13789.

The following formulae may be used to deriveelemental U-values (taking the unheated space intoaccount) for typical housing situations irrespective ofthe precise dimensions of the unheated space.

Uo = 1 /(1/U-Ru) or

U = 1 /(1/Uo+Ru)

Diagram 11 Para. A.3.1 Concrete slab-on-ground floor

Edge insulation (min themalresistance of 0.7m2K/W)

150mm dense concrete

100mm thermal insulation(thermal conductivity 0.035W/mK)Damp proof membrane. Where radon

barrier required, ensure correctdetailing to prevent passage of radongas into dwelling - see TGD C.

Where: U – U-value of element adjacent tounheated space (W/m2K), taking theeffect of the unheated space intoaccount.

Uo – U-value of the element betweenheated and unheated spaces(W/m2K) calculated as if there wasno unheated space adjacent to theelement.

Ru – effective thermal resistance ofunheated space inclusive of allexternal elements (m2 K / W).

Ru for typical unheated structures (including garages,access corridors to flats, unheated conservatoriesand attic spaces) are given below.

This procedure can be used when the precise detailsof the structure providing an unheated space are notavailable, or not crucial.

(a) Integral and adjacent single garages orother similar unheated space.

The table gives Ru for single garages; use (0.5 x Ru)for double garages when extra garage is not fullyintegral, and (0.85 x Ru) for fully integral doublegarages. Single garage means a garage for one car;double garage means a garage for two cars.

(b) UNHEATED Stairwells and accesscorridors in flats

(c) Conservatory-style sunroom

This applies only where a conservatory – styleSunroom is not treated as a integral part of thedwelling i.e . is treated as an extension – seeparagraph 1.1.2.

26

Exposed facing wall

Unheated Stairwell orCorridor

Unexposed facing wall

Flat

Walls adjacentto unheatedspace

Corridor above or below

Flat

Number of walls between dwelling Ru

and conservatory/sunroom

One 0.06

Two (conservatory in angle of dwelling) 0.14

Three (conservatory in recess) 0.25

Garage or other similar unheatedspace

Single fully integral

Single fully integral

Single, partially integraldisplaced forward

Single, adjacent

Element betweengarageand dwelling

Side wall, end wall and floor

One wall and floor

Side wall, end wall and floor

One wall

Ru

0.33

0.25

0.26

0.09

Unheated space Ru

Stairwells:Facing wall exposed 0.82Facing wall not exposed 0.90

Access corridors:Facing wall exposed, corridor above or below 0.31Facing wall exposed, corridors above and below 0.23Facing wall not exposed, corridor above or below 0.43

27

(d) Small unheated attic spaces

In the case of room-in-roof construction, the U-valueof the walls of the room-in-roof construction and ofthe ceiling of the room below the space adjacent tothese walls can be calculated using this procedure.

Room in roof

Elements adjacentto an unheatedspace

U-value calculatedas per normal roof

The value of Ru that applies to 0.5W/m2K

28

GENERAL

B.1 This Appendix provides some basic guidancein relation to typical roof, wall and floorconstructions. Guidance is not exhaustive anddesigners and contractors should also have regard toother sources of relevant guidance e.g. BR.262,Thermal Insulation; avoiding risks, relevant standardsand good building practice.

B.2 For many typical roof, wall and floorconstructions, the thickness of insulation required toachieve a particular U-value can be calculatedapproximately by the use of the appropriate Tablefrom this Appendix. The Tables can also be used toestimate the U-value achieved by a particularthickness of insulating material. Higher performinginsulating materials, i.e. those with lower thermalconductivities, can achieve any given U-value with alower thickness of insulating material.

B.3 These Tables have been derived using themethods described in Appendix A, taking intoaccount the effects of repeated thermal bridgingwhere appropriate. Figures derived from the tablesshould be corrected to allow for any discrete non-repeating thermal bridging which may exist in theconstruction. A range of factors are relevant to thedetermination of U-values and the values given inthese Tables relate to typical constructions of thetype to which the Tables refer. The methodsdescribed In Appendix A can be used to calculate amore accurate U-value for a particular constructionor the amount of insulation required to achieve aparticular U-value.

B.4 Intermediate U-values and values of requiredthickness of insulation can be obtained from theTables by linear interpolation.

Example B1: Partially filled cavity

What is the U-value of the construction shown inDiagram 12?

Table 14 gives U-values of 0.29 W/m2K and 0.25W/m2K for 100 mm insulation of thermalconductivity of 0.035 W/mK and 0.030 W/mK respectively. By linear interpolation, the U-value ofthis construction, with 100 mm of insulation ofthermal conductivity of 0.032 W/mK, is 0.27 W/m2K.

Appendix B: Fabric Insulation: Additional Guidance for CommonConstruction - including Tables of U-values

Diagram 12 Para. B.2 Partially filled cavity

102mm brick outer leaf

Cavity (min. 40 mm residualcavity)

100mm thermal insulation(thermal conductivity 0.032W/mK)

100mm dense concrete blockinner leaf

13mm lightweight plaster

HEAT FLOW

29

Example B2: Timber frame wall

What is the U-value of this construction?Table 19 gives the U-value for 150 mm of insulationof thermal conductivity of 0.04 W/mK as 0.27W/m2K.

Example B3: Pitched roof

What is the U-value of this construction?Table 6 gives the U-value for 250 mm of insulation ofthermal conductivity of 0.04 W/mK as 0.16 W/m2 K.

ROOF CONSTRUCTIONS

B.5.1 Construction R1: Tiled or slatedpitched roof, ventilated roof space,insulation at ceiling level.

B.5.1.1 R1(a) Insulation between and overjoists

Diagram 15 Para. B51.1 Insulation between and over joists

Tiled or slated roof

35mm timber battens

2mm sarking felt

Rafters

Insulation between and overjoists

Vapour control layer(where appropriate)

13mm plasterboard


19mm tiles

35mm timber battens

2mm sarking felt

Rafters

250mm thermalinsulation (thermalconductivity 0.04W/mK) with 100mmlaid between timberceiling joists and150mm over joistswith vapour controllayer, whereappropriate

13mm plasterboardceiling


Diagram 14 Para. B.2 Pitched roof

HEAT FLOW

Diagram 13 Para. B.2 Timber frame wall

102mm brick outerleaf

Cavity

Sheathing ply

150mm insulatingmaterial betweenstuds(thermal conductivity0.04 W/mK)


13mm plasterboard

HEAT FLOW

30

Installation guidelines and precautionsCare is required in design and construction,particularly in regard to the following:

Provision of adequate roof space ventilationAdequate ventilation is particularly important toensure the prevention of excessive condensation incold attic areas. See relevant guidance in TGD F.

Minimising transfer of water vapour fromoccupied dwelling area to cold attic spaceIn addition to ensuring adequate ventilation,measures should be taken to limit transfer of watervapour to the cold attic. Care should be taken toseal around all penetrations of pipes, ducts, wiring,etc. through the ceiling, including provision of aneffective seal to the attic access hatch. Use of avapour control layer at ceiling level, on the warmside of the insulation, will assist in limiting vapourtransfer, but cannot be relied on as an alternative toventilation. In particular, a vapour control layershould be used where the roof pitch is less than 15o,or where the shape of the roof is such that there isdifficulty in ensuring adequate ventilation, e.g. room-in-the-roof construction.

Minimising the extent of cold bridging. Particular areas of potential cold bridging includejunctions with external walls at eaves and gables, andjunctions with solid party walls. Gaps in theinsulation should be avoided and the insulationshould fit tightly against joists, noggings, bracing etc.Insulation joints should be closely butted and jointsin upper and lower layers of insulation should bestaggered.

Protecting water tanks and pipework againstthe risk of freezing.All pipework on the cold side of the insulationshould be adequately insulated. Where the coldwater cistern is located in the attic, as is normallythe case, the top and sides of the cistern should beinsulated. The area underneath the cistern should beleft uninsulated and continuity of tank and ceilinginsulation should be ensured e.g. by overlapping thetank and ceiling insulation. Provision should be madeto ensure ventilation of the tank.

Ensuring that there is no danger fromoverheating of electric cables or fittings.Cables should be installed above the insulation.Cables which pass through or are enclosed ininsulation should be adequately rated to ensure thatthey do not overheat. Recessed fittings should haveadequate ventilation or other means to preventoverheating.

Providing for access to tanks, services andfittings in the roofspace.Because the depth of insulation will obscure thelocation of ceiling joists, provision should be madefor access from the access hatch to the cold watertank and to other fittings to which access foroccasional maintenance and servicing may berequired.

Total Thermal conductivity of insulation (W/m K)thickness ofinsulation 0.040 0.035 0.030 0.025 0.020(mm) U-Value of construction (W/m2K)

150 0.26 0.24 0.21 0.18 0.15175 0.23 0.20 0.18 0.15 0.13200 0.20 0.18 0.15 0.13 0.11225 0.18 0.16 0.14 0.12 0.10250 0.16 0.14 0.12 0.10 0.09275 0.14 0.13 0.11 0.09 0.08300 0.13 0.12 0.10 0.09 0.07

Table 6 U-values for tiled or slated pitchedroof, ventilated roof space,insulation placed between and overjoists at ceiling level

This table is derived for roofs with:Tiles or slates, felt, ventilated roof space, timber joists (λ =0.13) with the spaces between fully filled with insulation andthe balance of insulation above and covering joists. (seeDiagram 20). Calculations assume a fractional area of timber thermalbridging of 8%.

31

B.5.1.2 R1(b) Insulation between andbelow joists.Insulation is laid in one layer between the joists,protruding above them where its depth is greater,and leaving air gaps above the joists. A compositeboard of plasterboard with insulation backing is usedfor the ceiling.

Installation guidelines and precautions.Similar guidelines and precautions apply as for R1(a)above.

B.5.2 Construction R2: Tiled or slatedpitched roof, occupied or unventilatedroof space, insulation on roof slope.

B.5.2.1 R2(a) Insulation between andbelow rafters, 50 mm ventilated cavitybetween insulation and sarking felt.

Diagram 17 Para. B.5.2.1Insulation between and below rafters

Tiles or slates onbattens, sarking felt andrafters

50mm ventilated airspace

Insulation between andbelow rafters



Occupied / unventilated roof space

Thickness of Thermal conductivity of insulation (W/m K)insulationbelow joists 0.040 0.035 0.030 0.025 0.020(mm) U-Value of construction (W/m2K)

10 0.26 0.26 0.25 0.25 0.2420 0.24 0.24 0.23 0.23 0.2230 0.23 0.22 0.22 0.21 0.1940 0.22 0.21 0.20 0.19 0.1850 0.20 0.20 0.19 0.18 0.1660 0.19 0.19 0.18 0.16 0.1570 0.18 0.18 0.17 0.15 0.1480 0.18 0.17 0.16 0.15 0.1390 0.17 0.16 0.15 0.14 0.12100 0.16 0.15 0.14 0.13 0.11110 0.16 0.15 0.14 0.12 0.11120 0.15 0.14 0.13 0.12 0.10

Table 7 U-values for tiled or slated pitchedroof, ventilated roof space,insulation placed between andbelow joists at ceiling level

This table is derived for roofs as in Table 6 but with 150 mmof insulation (λ = 0.04) between ceiling joists, and theremainder below the joists. Insulation of thickness andthermal conductivity as shown in the table is below joists.(See Diagram 16).

(The insulation thickness shown does not include thethickness of plasterboard in composite boards).

Diagram 16 Para. B.5.1.2 Insulation between and below joists

150mm insulationbetween ceilingjoists

Additional insulationbelow joists

Vapour controllayer


32

Installation guidelines and precautions.The insulation is installed in two layers, one betweenthe rafters (and battens) and the second below andacross them. To limit water vapour transfer andminimise condensation risks, a vapour control layeris required on the warm side of the insulation. Nomaterial of high vapour resistance, e.g. facing layerattached to insulation to facilitate fixing, should beincluded within the overall thickness of insulation.Care must be taken to prevent roof timbers andaccess problems interfering with the continuity ofinsulation and vapour control layer.

Provision must be made for ventilation top andbottom of the 50mm ventilation gap on the cold sideof the insulation.

Care should be taken to avoid thermal bridging atroof-wall junctions at eaves, gable walls and partywalls.

The table above assumes that the thermal

conductivity of insulation between and below therafters is the same. If different insulation materialsare used, the material on the warm side (i.e. belowrafters) should have a vapour resistance no lowerthan that on the cold side (i.e. between rafters).

B.5.2.2 R2(b): Insulation above andbetween rafters, slate or tile underlay ofbreather membrane type.

This table is derived for roofs with:Ties or slates, tiling battens, vapour permeable membrane (asunderlay), counter battens, insulation layer over rafters, rafterswith insulation of depth 100 mm fitted between. (See diagram18).Insulation between and over rafters has the same thermalconductivity.A fractional area of timber of 8% is assumed.

Total thickness Thermal conductivity of insulation (W/m K)of insulationbelow joists 0.040 0.035 0.030 0.025 0.020(mm) U-Value of construction (W/m2K)

120 0.34 0.31 0.27 0.24 0.20140 0.29 0.26 0.23 0.20 0.16160 0.25 0.23 0.20 0.17 0.14180 0.22 0.20 0.17 0.15 0.12200 0.20 0.18 0.16 0.13 0.11220 0.18 0.16 0.14 0.12 0.10240 0.17 0.15 0.13 0.11 0.09260 0.15 0.14 0.12 0.10 0.08

Table 8 U-values for tiled or slated pitchedroof, occupied or unventilated roofspace, insulation placed betweenand below rafters

This table is derived for roofs with:Tiles or slates, felt, rafters of depth 150 mm (λ = 0.13), 50 mmventilated air space above insulation, 100 mm insulationbetween rafters, balance of insulation below and across rafters.(See Diagram 17).A fractional area of timber of 8% is assumed. Battens may befixed to the underside of the rafters to increase rafter depth ifnecessary.

Diagram 18 Para.5.2.2Insulation above and between rafters

Tiles or slates on battens

Vapour permeablemembrane (underlay)

Counter battens

Insulation over andbetween rafters


13mm plasterboard

Total thickness Thermal conductivity of insulation (W/m K)of insulation(mm) 0.040 0.035 0.030 0.025 0.020

U-Value of construction (W/m2K)

120 0.33 0.30 0.27 0.23 0.20140 0.28 0.25 0.22 0.19 0.16160 0.25 0.22 0.19 0.17 0.14180 0.22 0.20 0.17 0.15 0.12200 0.20 0.18 0.15 0.13 0.11220 0.18 0.16 0.14 0.12 0.10240 0.16 0.15 0.13 0.11 0.09260 0.15 0.13 0.12 0.10 0.08

Table 9 U-values for tiled or slated pitchedroof, occupied or unventilated roofspace, insulation placed betweenand above rafters.

Installation guidelines and precautions

The effective performance of this system is criticallydependent on the prevention of air and watervapour movement between the warm and cold sidesof the insulation. Only systems which are certified orshown by test and calculation as appropriate for thisfunction, (see TGD D, Paragraph 1.1 (a) and (b))should be used. The precise details of constructionare dependent on the insulation and roof underlaymaterials to be used. Installation should be carriedout precisely in accordance with the proceduresdescribed in the relevant certificate.

In general, the insulation material must be of lowvapour permeability, there should be a tight fitbetween adjacent insulation boards, and betweeninsulation boards and rafters. All gaps in theinsulation (e.g. at eaves, ridge, gable ends, aroundrooflights and chimneys, etc.) should be sealed withflexible sealant or expanding foam.

Care should be taken to avoid thermal bridging atroof-wall junctions at eaves, gable walls and partywalls.

B.5.3 Construction R3: Flat roof, timberjoists, insulation below deck

B.5.3.1 R3(a) Insulation between joists,50 mm air gap between insulation androof decking

The insulation is laid between the joists. The depthof the joists is increased by means of battens ifrequired.

This table is derived for roofs with:Weatherproof deck, ventilated air space, insulation as givenabove between timber joists (λ = 0.13), 13 mm plasterboard(λ= 0.25). (See Diagram 19).The calculations assume a fractional area of timber of 8%.


A vapour control layer sealed at all joints, edges andpenetrations, is required on the warm side of theinsulation, and a ventilated air space as specified inTGD F provided above the insulation. Crossventilation should be provided to each and everyvoid. When installing the insulation, care is neededto ensure that it does not block the ventilation flowpaths.

The integrity of the vapour control layer should beensured by effective sealing of all servicepenetrations, e.g. electric wiring, or by provision of aservices zone immediately above the ceiling, butbelow the vapour control layer.

The roof insulation should connect with the wallinsulation so as to avoid a cold bridge at this point.

33



150 0.29 0.26 0.24 0.21 0.18175 0.25 0.23 0.20 0.18 0.16200 0.22 0.20 0.18 0.16 0.14225 0.20 0.18 0.16 0.14 0.12250 0.18 0.16 0.15 0.13 0.11275 0.16 0.15 0.13 0.12 0.10300 0.15 0.14 0.12 0.11 0.09

Table 10: U-values for timber flat roof,insulation between joists, 50mmventilated air gap betweeninsulation and roof decking.

Diagram 19 Para. B.5.3.1Timber flat roof, insulation between joists

Waterproofdecking

50mmventilated airspace

Insulationbetween joists

Vapourcontrol layer

13mmplasterboard

34

B.5.3.2 R3(b) Insulation between andbelow joists, 50 mm air gap betweeninsulation and roof decking

The insulation may be installed in two layers, onebetween the joists as described above, and thesecond below the joists. This lower layer may be inthe form of composite boards of plasterboardbacked with insulation, with integral vapour barrier,fixed to the joists. The edges of boards should besealed with vapour-resistant tape.

This table is derived for roofs as in Table 10 above, exceptwith 100 mm of insulation of λ = 0.04 between 150 mm joists,and composite board below joists consisting of 10 mmplasterboard (λ = 0.25) backed with insulation as specified inthis table.

B.5.4 Construction R4: Sandwich warmdeck flat roof

The insulation is installed above the roof deck butbelow the weatherproof membrane. The structuraldeck may be of timber, concrete or metal.

This table is derived for roofs with:12 mm felt bitumen layers (λ = 0.23), over insulation as given inthe table, over 50 mm screed (λ = 0.41), over 150 mm concreteslab (λ = 2.30), over 13 mm plasterboard (λ = 0.25). (SeeDiagram 20).

Thickness of Thermal conductivity of insulation (W/m K)insulationbelow joists 0.040 0.035 0.030 0.025 0.020(mm) U-Value of construction (W/m2K)

20 0.34 0.33 0.32 0.31 0.2940 0.29 0.28 0.27 0.25 0.2260 0.25 0.24 0.22 0.21 0.1880 0.22 0.21 0.20 0.18 0.15

100 0.20 0.19 0.17 0.15 0.13120 0.18 0.17 0.15 0.14 0.12140 0.17 0.15 0.14 0.12 0.11160 0.15 0.14 0.13 0.11 0.10

Table 11: U-values for timber flat roof,insulation between and belowjoists, 50mm ventilated air gapbetween insulation and roofdecking.

Diagram 20 Para. B.5.4Sandwich warm deck flat roof above a concrete structure

Waterproofmembrane

Insulation

High performancevapour barrier

Concrete screed

Dense concreteroofslab



100 0.34 0.30 0.26 0.22 0.18125 0.28 0.25 0.22 0.18 0.15150 0.24 0.21 0.18 0.15 0.13175 0.21 0.18 0.16 0.13 0.11200 0.18 0.16 0.14 0.12 0.10225 0.16 0.14 0.13 0.11 0.09250 0.15 0.13 0.11 0.10 0.08

Table 12: U-values for sandwich warm deckflat roof.

3535



100 0.40 0.35 0.31 0.26 0.22125 0.33 0.29 0.26 0.22 0.18150 0.28 0.25 0.22 0.18 0.15175 0.24 0.22 0.19 0.16 0.13200 0.22 0.19 0.17 0.14 0.11225 0.19 0.17 0.15 0.13 0.10250 0.18 0.16 0.14 0.11 0.09275 0.16 0.14 0.12 0.10 0.08300 0.15 0.13 0.11 0.10 0.08

Table 13: U-values for inverted warm deckflat roof.


The insulation boards are laid over and normally fullybonded to a high performance vapour barriercomplying with BS 747 which is bonded to the roofdeck. The insulation is overlaid with a waterproofmembrane, which may consist of a single layermembrane, a fully-bonded built-up bitumen roofingsystem, or mastic asphalt on an isolating layer. At theperimeter, the vapour barrier is turned up and backover the insulation and bonded to it and theweatherproof membrane. Extreme care is requiredto ensure that moisture can not penetrate thevapour barrier.

The insulation should not be allowed to get wetduring installation.

There should be no insulation below the deck. Thiscould give rise to a risk of condensation on theunderside of the vapour barrier.

Thermal bridging at a roof / wall junction should beavoided.

B.5.5 Construction R5: Inverted warmdeck flat roof: insulation to falls aboveboth roof deck and weatherproofmembrane

Insulation materials should have low waterabsorption, be frost resistant and should maintainperformance in damp conditions over the long term.To balance loss of performance due to the dampconditions and the intermittent cooling effect ofwater passing through and draining off from thewarm side of the insulation, the insulation thicknesscalculated as necessary for dry conditions should beincreased by 20%.

This table is derived for roofs with:50 mm gravel ballast (λ = 2.0) over insulation over 10 mmmastic asphalt (λ = 0.50) over 40 mm screed (λ = 0.41) over150 mm concrete (λ = 2.30) over 13 mm plasterboard (λ =0.25). Insulation thicknesses have been increased by 20% tobalance loss of performance due to rain water flow. (SeeDiagram 21).

Diagram 21 Para. B.5.5Inverted warm deck roof with concrete structure

Paving slab or ballast

Filtration layer

Insulation (low waterabsorptivity, frostresistance)

Asphalt orwaterproofmembrane

Concrete screed

Concrete roofslab

36

Installation guidelines and precautionsThe insulation is laid on the waterproof membrane.A filtration layer is used to keep out grit, which couldeventually damage the weatherproof membrane. Theinsulation must be restrained to prevent wind upliftand protected against ultraviolet degradation. This isusually achieved by use of gravel ballast, paving stonesor equivalent restraint and protection. The insulationshould have sufficient compressive strength towithstand the weight of the ballast and any otherloads.

Rainwater will penetrate the insulation as far as thewaterproof membrane. Drainage should be providedto remove this rainwater. To minimise the effect ofrain on performance, insulation boards should betightly jointed (Rebated or tongued-and-groovededges are preferred), and trimmed to give a close fitaround upstands and service penetrations.

To avoid condensation problems, the thermalresistance of the construction between theweatherproof membrane and the heated space is atleast 0.15 m2K/W. However, this thermal resistanceshould not exceed 25% of the thermal resistance ofthe whole construction.

Thermal bridging at roof / wall junctions should beavoided.

WALL CONSTRUCTIONS

B.6.1. W1: Cavity walls, insulation incavity, cavity retained (partial fill)

B.6.1.1 W1(a) Brick or rendered denseconcrete block external leaf, partial fillinsulation, dense concrete block inner leaf,plaster or plasterboard internal finish.

The following tables deal with walls with maximumoverall cavity width of 150mm, which is the greatestcavity width for which details of construction aregiven in I.S. 325. Where it is proposed to use widercavity widths, full structural and thermal design willbe necessary.

Diagram 22 Para. B.6.1.1 Cavity wall with partial-fill insulation

External leaf (brick or dense concrete block withexternal render)

Air space (min. 40mm)

Insulation

Inner leaf (concrete block, plaster orplasterboard)

Total thickness Thermal conductivity of insulation (W/mK)of insulation(mm) 0.040 0.035 0.030 0.025 0.020


60 0.48 0.43 0.39 0.33 0.2880 0.39 0.35 0.31 0.26 0.22

100 0.32 0.29 0.25 0.22 0.18

Table 14: U-values for brick (or rendereddense concrete block) external leaf,partial fill insulation, denseconcrete block inner leaf, plaster(or plasterboard) internal finish.

This table is derived for walls with:102 mm clay brickwork outer leaf (λ= 0.77), 50 mm airspace, insulation as specified in table, 100 mm concreteblock inner leaf (density - 1800 kg/m3, λ = 1.13), 13 mmdense plaster (λ = 0.57). (See Diagram 22). The effects ofwall ties are assumed to be negligible.

37

The insulation thickness required to achieve a givenU-value may be reduced by using lightweightconcrete insulating blocks for the inner leaf, asshown in the table below.

Note that the sound attenuation performance oflightweight blocks is not as good as that of heavierblocks. This may limit their suitability for use in theinner leafs of attached dwellings.


Insulation should be tight against the inner leaf. Anyexcess mortar should be cleaned off before fixinginsulation. The insulation layer should be continuousand without gaps. Insulation batts should butt tightlyagainst each other. Mortar droppings on batts shouldbe avoided. Batts should be cut and trimmed to fittightly around openings, cavity trays, lintels, sleevedvents and other components bridging the cavity, andshould be adequately supported in position.

Methods of reducing thermal bridging at openingsare illustrated in Section I above. Other criticallocations where care should be taken to limitthermal bridging include roof-wall junctions and wall-floor junctions. The method of cavity closure usedshould not cause thermal bridge at the roof-walljunction. Wall and floor insulation should overlap by200 mm, or by 100 mm where lightweight insulatingblocks are used for inner leaf at this position.

B.6.1.2 W1(b): As W1(a) except withinsulation partly in cavity and partly asinternal lining.

If composite boards of plasterboard backed withinsulation (of similar conductivity to that used in thecavity) are used internally, tables 14 and 15 can betaken as applying to the total insulation thickness(cavity plus internal) If internal insulation is placedbetween timber studs, total insulation thickness willbe slightly higher due to the bridging effect of thestuds. Table 16 applies in this case.

Lower U-values, or reduced insulation thickness, canbe achieved by using insulating concrete blockwork(rather than dense concrete) between the cavity andinternal insulation.

Insulation partly in cavity and partly as internal lininghelps minimise thermal bridging. Internal insulationlimits thermal bridging at floor and roof junctions,whereas cavity insulation minimises thermal bridgingat separating walls and internal fixtures.



60 0.40 0.37 0.34 0.30 0.2580 0.34 0.31 0.27 0.24 0.20

100 0.29 0.26 0.23 0.20 0.17

Table 15: U-values for construction as Table14 except for lightweight concreteblock inner leaf.

This table is derived for walls as in Table 14, exceptheavyweight concrete block inner leaf replaced with 100 mminsulating block (λ = 0.18). Calculations assume a 7% fractional area of mortar (λ =0.88) bridging the inner leaf.

Total thickness Thermal conductivity of insulation (W/m K)of insulationbetween studs 0.040 0.035 0.030 0.025 0.020(mm) U-Value of construction (W/m2K)

40 0.31 0.30 0.29 0.27 0.2660 0.27 0.26 0.25 0.23 0.21

Table 16: U-values for brick (or rendered denseconcrete block) external leaf, 60mmpartial fill insulation (λ = 0.035),dense concrete block inner leaf,plasterboard fixed to timber studs,insulation between studs.

This table is derived for walls as in Table 14 above, except with60 mm of insulation of λ = 0.035 in cavity, and insulation asspecified in the table applied to the internal surface of the wallbetween timber studs (λ = 0.13) of fractional area 8%, with awall finish of 13 mm plasterboard (λ = 0.25).

38


Installation of insulation in the cavity should followthe guidelines given above for construction W1(a)(partial-fill cavity insulation), and installation of theinternal lining should follow the guidelines givenbelow for construction W4 (hollow-block).

B.6.2. Construction W2: Cavity walls,insulation in cavity, no residual cavity (fullfill)

The insulation fully fills the cavity. Insulation may bein the form of semi-rigid batts installed as wallconstruction proceeds, or loose-fill material blowninto the cavity after the wall is constructed; theformer is considered here. Insulation materialsuitable for cavity fill should not absorb water bycapillary action and should not transmit water fromouter to inner leaf. Such insulation may extendbelow dpc level.

The insulation thickness required to achieve a givenU-value may be reduced by using insulating concreteblocks for the inner leaf, as shown in the table below.

Diagram 23 Para. B.6.2 Cavity wall with full-fill insulation

External leaf (rendered dense concreteblock)

Insulation

Inner leaf (concrete block,plaster or plasterboard)



60 0.51 0.46 0.41 0.35 0.2980 0.41 0.37 0.32 0.27 0.22

100 0.34 0.30 0.26 0.22 0.18120 0.29 0.26 0.22 0.19 0.16140 0.25 0.22 0.20 0.17 0.13160 0.22 0.20 0.17 0.15 0.12

This table is derived for walls with:

20 mm external rendering (λ = 0.57), 102 mm clay brickworkouter leaf (λ = 0.77), insulation as specified in table, 100 mmconcrete block inner leaf (medium density - 1800 kg/m3, λ =1.13), 13 mm dense plaster (λ = 0.57). The effects of wall tiesare assumed to be negligible. (See Diagram 23).

Table 17: U-values for rendered denseconcrete block external leaf, full-fillinsulation dense concrete blockinner leaf, plaster (or plasterboard)internal finish.



60 0.43 0.39 0.35 0.31 0.2680 0.35 0.32 0.29 0.25 0.21

100 0.30 0.27 0.24 0.21 0.17120 0.26 0.23 0.21 0.18 0.15140 0.23 0.21 0.18 0.16 0.13160 0.21 0.18 0.16 0.14 0.11

Table 18: U-values for rendered denseconcrete block external leaf, full-fillinsulation, lightweight concreteblock inner leaf, plaster (orplasterboard) internal finish.

This table is derived for walls as above, except heavyweightconcrete block inner leaf replaced with 100 mm insulatingblock (λ = 0.18). Calculations assume a 7% fractional area of mortar (λ= 0.88)bridging the inner leaf.

39


Only certified insulation products should be used,and the installation and other requirements specifiedin such certificates should be fully complied with. Inparticular, regard should be had to the exposureconditions under which use is certified and anylimitations on external finish associated therewith.

Guidance on minimising air gaps and infiltration inpartial-fill cavity insulation applies also to full-fillinsulation.

Methods of reducing thermal bridging aroundopenings are illustrated in Section 1 above.

B.6.3 Construction W3: Timber framewall, brick or rendered concrete blockexternal leaf

B.6.3.1 W3(a) Insulation between studs

The insulation is installed between studs, whosedepth equals or exceeds the thickness of insulationspecified.

In calculating U-values, the fractional area of timberbridging the insulation should be checked. Accountshould be taken of all timber elements which fullybridge the insulation, including studs, top and bottomrails, noggings, timbers around window and dooropenings and at junctions with internal partitions,party walls and internal floors. In the Table afractional area of 12% is assumed.


Air gaps in the insulation layer, and between it andthe vapour barrier, should be avoided. Insulationbatts should be friction fitted between studs tominimise gaps between insulation and joists. Adjacentinsulation pieces should butt tightly together.Particular care is needed to fill gaps between closely-spaced studs at wall/wall and wall/floor junctions, andat corners of external walls.

A vapour control layer should be installed on thewarm side of the installation. There should be nolayers of high vapour resistance on the cold side ofthe insulation.

Care is required to minimise thermal bridging of theinsulation by timber noggings and other inserts.

B.6.3.2 W3(b:) Insulation between andacross studs

Where the chosen stud depth is not sufficient toaccommodate the required thickness of insulation,insulation can be installed to the full depth between



100 0.38 0.35 0.32 0.29 0.26125 0.32 0.29 0.27 0.24 0.22150 0.27 0.25 0.23 0.21 0.18175 0.24 0.22 0.20 0.18 0.16

Table 19: U-values for brick (or rendereddense concrete block) external leaf,timber frame inner leaf, insulationbetween timber studs, plasterboardinternal finish.

This table is derived for walls with:102 mm clay brickwork outer leaf (λ = 0.77), 50 mm aircavity, breather membrane, 12 mm sheathing board (λ =0.14), insulation between timber studs (λ = 0.13), vapourcontrol layer, 13 mm plasterboard (λ = 0.25). (See Diagram24).The calculations assume a fractional area of timber thermalbridging of 12%.

Diagram 24 Para. B.6.3.1Timber frame wall, insulation between framing timbers

External leaf (brick or rendered denseconcrete block)

50mm air cavity

Breather membrane

Sheathing board

Insulation


Plasterboard

40

the studs with additional insulation being provided asan internal lining. This additional insulation may beeither in the form of plasterboard/insulationcomposite board or insulation between timberbattens, to which the plasterboard is fixed.

The vapour control layer should be on the warmside of the insulation. If different types of insulationare used between and inside the studs, the vapourresistance of the material between the studs shouldnot exceed that of the material across them.

B.6.4 Construction W4: Hollow concreteblock wall, rendered externally, internalinsulation lining with plasterboard finish.

The insulation is installed on the inner face of themasonry walls. It may be installed betweenpreservative-treated timber studs fixed to the wall,or in the form of composite boards of plaster backedwith insulation, or as a combination of these.


Air Movement

Air gaps in the insulation layer should be kept to aminimum. If using insulation between timber studs,there should be no gaps between insulation andstuds, between insulation and the vapour controllayer, between butt joints in the insulation, aroundservice penetrations, etc. If using composite boards,they should be tightly butted at edges, and shouldprovide complete and continuous coverage of theexternal wall.

When mounting composite boards on plaster dabsor timber battens, there is a danger that air will beable to circulate behind the insulation, reducing itseffectiveness. To minimise such air movement, the airgap behind the boards should be sealed along topand bottom, at corners and around window anddoor openings e.g. with continuous ribbon of plasteror timber studs.

Total thickness Thermal conductivity of insulation (W/m K)of insulationacross studs 0.040 0.035 0.030 0.025 0.020(mm) U-Value of construction (W/m2K)

20 0.31 0.31 0.30 0.29 0.2740 0.27 0.26 0.25 0.23 0.2160 0.24 0.23 0.21 0.20 0.17

Table 20: U-values for brick (or rendereddense concrete block) external leaf,timber frame inner leaf, insulationbetween 100mm timber studs,additional insulation, plasterboardinternal finish.

This table is derived for walls as in W3(a) above, except with100 mm of insulation (λ = 0.04) between 100 mm studs andan additional layer of insulation as specified in the Tableacross the studs.

Diagram 25 Para. B.6.4 Hollow-block wall, internal insulation lining

Rendered hollow concreteblock

Insulation


Plasterboard

41

Condensation

A vapour control layer (e.g. 500 gauge polythene)should be installed on the warm side of theinsulation to minimise the risk of interstitialcondensation on the cold masonry behind theinsulation. Care should be taken to avoid gaps in thevapour control layer at all joints, edges and servicepenetrations. The location of service runs in the airgap on the cold side of the insulation should, wherepossible, be avoided. Where this proves unavoidablefor particular service runs, care should be taken toseal around any penetrations of the insulation layerand vapour control layer.

Thermal Bridging

Care should be taken to minimise the impact ofthermal bridging.

Methods of reducing thermal bridging aroundopenings are illustrated in Section 1 above.

Other areas where there is a risk of significantthermal bridging include:

Junctions with solid party walls and partitions.

Internal partition or party walls of solid denseconcrete blockwork can create significant thermalbridge effects at junctions with single leaf masonryexternal walls. The thermal bridge effect can beadequately limited either by the use of lightweightconstruction in the internal wall or by returninginsulation of minimum thermal resistance1.00 m2K/W for a distance of at least 1m on theinternal wall.

Junctions with intermediate floors.

The external walls in the floor space of intermediatefloors should be insulated and protected againstvapour movement. Along the wall running parallel tothe joists, insulation can be placed between the lastjoist and the wall. Where the joists are perpendicularto the wall, the insulation and vapour control layershould be continuous through the intermediate floorspace and should be carefully cut to fit around thejoist ends.



75 0.48 0.44 0.40 0.35 0.31100 0.38 0.35 0.31 0.28 0.24125 0.32 0.29 0.26 0.23 0.20150 0.27 0.25 0.22 0.20 0.17175 0.24 0.22 0.19 0.17 0.15

Table 21: U-values for hollow-block wall,rendered externally, plasterboardfixed to timber studs internally,insulation between studs.



40 0.61 0.56 0.51 0.45 0.3850 0.53 0.49 0.44 0.38 0.3260 0.47 0.43 0.38 0.33 0.2870 0.42 0.38 0.34 0.29 0.2480 0.38 0.34 0.30 0.26 0.2290 0.35 0.31 0.28 0.24 0.19

100 0.32 0.29 0.25 0.22 0.18110 0.30 0.27 0.23 0.20 0.16120 0.28 0.25 0.22 0.18 0.15130 0.26 0.23 0.20 0.17 0.14140 0.24 0.22 0.19 0.16 0.13150 0.23 0.20 0.18 0.15 0.12

Table 21A: U-values of hollow-block wall,rendered externally, compositeinsulation/plasterboard internally,fixed to timber battens [orplaster dabs]

These tables are derived for walls with:19 mm external rendering (λ = 1.00), 215 mm hollow concreteblock (thermal resistance = 0.21 W/m2K), insulation fixed asstated, vapour control layer, 13 mm plasterboard (λ = 0.25).(See Diagram 25).The calculations assume a fractional area of timber thermalbridging (or plaster dabs) of 8%.

42

Stairs, cupboards and other fittings supported onor abutting the external wall.

Insulation should be carried through behind suchfittings.

Ducts, e.g. Soil and vent pipe ducts, againstexternal walls.

Insulation should be continuous at all such ducts, i.e.the insulation should be carried through on eitherthe external or internal side of such ducts. Wherethe insulation is on the external side, particular careshould be taken to prevent ingress of cold externalair where ducts etc. penetrate the insulation.

FLOOR CONSTRUCTIONS

B.7.1 Construction F1: Ground floor:concrete slab-on-ground. Insulation underslab or under screed

For continuous and uniform insulation under the fullground floor area, the insulation thickness requiredto achieve prescribed U-values for slab-on-groundfloors are given below. These tables apply whetherthe insulation is located under the slab or under thescreed.

Table 22 allows estimation of the U-value of aninsulated floor from the ratio of the length ofexposed perimeter to floor area and the thermalresistance of the applied insulation. Table 23 gives thethickness of insulation required to achieve a given U-value when the ratio of exposed perimeter to floorarea and the thermal conductivity of the material isknown. Both tables are derived for uniform full-floorinsulation, ground conductivity of 2.0 W/m2K and fullthickness of walls taken to be 0.3m.


The insulation may be placed above or below thedpm/radon barrier. The insulation should not absorbmoisture and, where placed below the dpm/radonbarrier, should perform well under prolonged dampconditions and should not be degraded by anywaterborne contaminants in the soil or fill.

The insulation should have sufficient load-bearingcapacity to support the floor and its loading.

The insulation is laid horizontally over the wholearea of the floor. Insulation boards should be tightlybutted, and cut to fit tightly at edges and aroundservice penetrations.

Diagram 26 Para. B.7.1

Concrete slab-on-ground floor, insulationunder slab

Damp proof membrane. Where radonbarrier required, ensure correct detailingto prevent passage of radon gas intodwelling - See TGD C.

Concrete screed(optional)

Concrete floor slab

Insulation

Diagram 27 Para. B.7.1

Concrete slab-on-ground floor, insulationunder screed

Screed

Insulation

Damp proofmembrane

Concrete floor slab

Where radon barrier required, ensurecorrect detailing to prevent passage ofradon gas into dwelling - See TGD C.

43

Care should be taken to prevent damage ordislodgement of insulation during floor laying. If thedpm is placed below the insulation, the jointsbetween insulation boards should be taped toprevent wet screed from entering when beingpoured. If the slab/screed is power-floated, theexposed edges of perimeter insulation should beprotected during power-floating, e.g. by boards, orthe areas close to the edge of the floor should behand trowelled.

To minimise thermal bridging at floor-wall junctions,edge insulation of minimum thickness 25 mm shouldbe placed vertically at the edge of the screed at thefloor perimeter. With internally insulated externalwalls (including timber-frame), the floor perimeterinsulation should meet the wall insulation to avoid athermal bridge.

With cavity walls, thermal bridging via the inner leafis difficult to avoid, but adequate provision to limit itshould be made by ensuring that cavity insulation andfloor insulation overlap by at least 200 mm, or by100 mm if insulating blocks (of density not greaterthan 1200 kg/m3) are used for the inner leaf betweenthe overlapping insulation.

Thermal conductivity of insulation (W/mK)P/A (m-1)

0.040 0.035 0.030 0.025 0.020

Insulation thickness (mm)

0.1 10 8 7 6 50.2 64 56 48 40 320.3 88 77 66 55 440.4 100 88 75 63 500.5 110 96 82 69 550.6 116 101 87 72 560.7 120 105 90 75 600.8 123 108 93 77 620.9 126 110 94 79 631.0 128 112 96 80 64

Table 23: Concrete slab-on-ground floors:Insulation thickness required for U-value of 0.25 W/m2K.

Table 22: U-value of insulated ground floor as a function of floor area, exposed perimeter and thermal resistance of added insulation (Uins).

Exposed Perimeter/Area(P/A) Thermal Resistance of Added Insulation

(m-1) [Rins] (m2K/W)

0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5 2.75 3.0 3.5 4.0

1.00 0.66 0.57 0.50 0.44 0.40 0.36 0.33 0.31 0.28 0.27 0.23 0.21

0.90 0.64 0.55 0.48 0.43 0.39 0.36 0.33 0.30 0.28 0.26 0.23 0.21

0.80 0.62 0.54 0.47 0.42 0.38 0.35 0.32 0.30 0.28 0.26 0.23 0.21

0.70 0.59 0.52 0.46 0.41 0.37 0.34 0.31 0.29 0.27 0.25 0.23 0.20

0.60 0.57 0.50 0.44 0.40 0.36 0.33 0.31 0.28 0.27 0.25 0.22 0.20

0.50 0.53 0.47 0.42 0.38 0.35 0.32 0.30 0.27 0.26 0.24 0.22 0.19

0.40 0.48 0.43 0.39 0.36 0.33 0.30 0.28 0.26 0.25 0.23 0.21 0.19

0.30 0.43 0.39 0.35 0.32 0.30 0.28 0.26 0.24 0.23 0.22 0.20 0.18

0.20 0.35 0.32 0.30 0.28 0.26 0.24 0.23 0.22 0.21 0.20 0.18 0.16

44

B.7.2 Construction F2: Ground floor:suspended timber floor, insulationbetween joist


Where mineral wool quilt insulation is used, theinsulation is supported on polypropylene netting or abreather membrane draped over the joists and heldagainst their sides with staples or battens. The fullthickness of insulation should extend for the fullwidth between joists. Insulation should not bedraped over joists, but cut to fit tightly betweenthem.

Alternatively, rigid or semi-rigid insulation boards,supported on battens nailed to the sides of thejoists, may be used.

Thermal bridging, and air circulation around theinsulation from the cold vented air space below,should be minimised. The insulation should fit tightlyagainst the joists and the flooring above. Carefulplacement of supporting battens (or staples) isrequired to achieve this. At floor-wall junctions theinsulation should extend to the walls. The spacebetween the last joist and the wall should be packed

Timber flooring


Ventilatedsubfloor

Note: Where radon barrier required,ensure correct detailing to prevent passageof radon gas into dwelling - See TGD C.

Diagram 28 Para. B.7.2Suspended timber floor with quilt insulation

Diagram 29 Para. B.7.2Suspended timber floor with rigid or semi-rigid board insulation

Timber flooring


Ventilatedsubfloor

Note: Where radon barrier required,ensure correct detailing to prevent passageof radon gas into dwelling - See TGD C.

Thermal conductivity of insulation (W/mK)P/A

(m-1) 0.040 0.035 0.030 0.025 0.020

U-value of Construction (W/m2K)

0.1 39 35 31 28 230.2 97 88 79 70 600.3 119 108 96 85 730.4 130 118 106 93 810.5 137 124 111 98 850.6 142 129 115 102 880.7 145 132 118 105 910.8 148 134 121 107 920.9 150 136 122 108 941.0 152 138 124 110 95

Table 24: Suspended timber ground floors:Insulation thickness required for U-value of 0.25 W/m2K.

This table is derived for:Suspended floor consisting of 20 mm timber flooring (λ = 0.13)on timber joists (λ = 0.13), with insulation between the joists.Ventilated sub-floor space underneath. (See Diagrams 28 and29).A fractional area of timber thermal bridging of 12% is assumed.

with mineral wool to the full depth of the joist.Where internal wall insulation is used, the floor andwall insulation should meet. Where cavity insulationis used, the floor insulation should be turned downon the internal face and overlap the cavity insulation,or insulating blocks used in the wall at this level.

Cross-ventilation should be provided to the sub-floor space to remove moisture.

Water pipes in the sub-floor space should beinsulated to prevent freezing.

B.7.3 Construction F3: Ground floor:suspended concrete floor

Installation guidance and precautions

If the walls are internally insulated, it isrecommended that the floor insulation be placedabove the floor structure, since it can then connectwith the wall insulation. Thermal bridging at thefloor-wall junction is difficult to avoid when insulationis placed below the floor structure.

If the walls are cavity insulated, floor insulation cannot connect with wall insulation, so some thermalbridging is inevitable. It can be minimised by usinginsulating blocks for the inner leaf betweenoverlapping floor and wall insulation. Insulation andinsulating blocks may be either above or below thefloor structure, but above is recommended. This willallow the use of less dense blocks (of lower thermalconductivity), since they will not have to support theweight of the floor. Also, above the structure theywill be above the dpc, where their lower moisturecontent will give a lower thermal conductivity thanbelow the dpc. Heat loss from the floor can befurther reduced by extending the cavity insulationdown to, or below, the lower edge of the suspendedfloor.

45

Thermal conductivity of insulation (W/mK)P/A

(m-1) 0.040 0.035 0.030 0.025 0.020Insulation thickness (mm)

0.1 19 17 14 12 100.2 69 60 52 43 350.3 87 76 65 54 440.4 96 84 72 60 480.5 102 89 77 64 510.6 106 93 80 67 530.7 109 96 82 69 550.8 112 98 84 70 560.9 114 99 85 71 571.0 115 101 86 72 58

This table is derived for floors with:65 mm screed (λ = 0.41) on insulation on 150 mm castconcrete (λ = 2.20). Full thickness of walls = 0.3 m, U-valueof sub-floor walls: 2 W/m2K. Height of floor surface aboveground level: 0.3 m. (See Diagrams 30 and 31).Unventilated sub-floor crawl space underneath.

Table 25: Suspended concrete ground floors:Insulation thickness required for U-value of 0.25 W/m2K.

Diagram 30 Para. B.7.3 Suspended reinforced concrete floor,internally insulated walls

Floor screed

Insulation

Suspendedconcrete floorslab

Diagram 31 Para. B.7.3 Suspended beam and block floor

Floor screed

Insulation

Beam andblock floor

46

B.7.4 Construction F4: Exposed floor:timber joists, insulation between joists


The flooring on the warm side of the insulationshould have a higher vapour resistance than theouter board on the cold side. If necessary, a vapourcheck should be laid across the warm side of theinsulation. Methods of avoiding thermal bridging atjunctions with internally insulated and cavityinsulated walls are similar to those described forsuspended timber ground floors above.

Diagram 32 Para. B.7.4Exposed timber floor, insulation between joists

Timber flooring


Plasterboard orsimilar



100 0.42 0.38 0.35 0.32 0.28120 0.36 0.33 0.30 0.27 0.24140 0.31 0.29 0.26 0.24 0.21160 0.28 0.26 0.23 0.21 0.19180 0.25 0.23 0.21 0.19 0.17200 0.23 0.21 0.19 0.17 0.15

Table 26: U-values for exposed timber floors,insulation between timber joists,plasterboard finish.

This table is derived for floors with:20 mm timber flooring (λ = 0.13), insulation as specified intable between timber joists (λ = 0.13) of equal depth, 13 mmplasterboard (λ = 0.25). The calculations assume a fractionalarea of timber thermal bridging of 12%. (See Diagram 32)

47

B.7.5 Construction F5: Exposed floor:solid concrete, insulation external


If the walls are internally insulated, this floorconstruction is not recommended. Floor insulationshould instead be located internally in order toconnect with the wall insulation.

With cavity wall insulation, thermal bridging may beminimised by supporting the external leafindependently, and continuing the external floorinsulation around the edge beam to connect with thecavity insulation as shown in Diagram 33.



60 0.54 0.48 0.42 0.36 0.3080 0.42 0.38 0.33 0.28 0.23

100 0.35 0.31 0.27 0.23 0.19120 0.30 0.26 0.23 0.19 0.16140 0.26 0.23 0.20 0.17 0.14160 0.23 0.20 0.18 0.15 0.12

This table is derived for floors with:150 mm cast concrete (λ = 1.35), insulation, 20 mm externalrender. (See Diagram 33).

Table 27: U-values for exposed concretefloors, external insulation,external render

Diagram 33 Para. B.7.5Exposed concrete floor, external insulation

Floor screed

Concrete floor

Insulationcontinued aroundedge beam

48

External Doors, Windows and Rooflights

Table 28: Indicative U-values (W/m2K) for windows, doors and rooflights

GAP WIDTH FRAME TYPE

TYPE EMISSIVITY BETWEEN WOOD OR METAL METAL WITHOUTPANES (mm) PVC-u WITH 12 mm THERMAL

THERMAL BREAK BREAK

WINDOWSSINGLE - - 4.8 - 5.7

0.89 6 3.1 3.5 4.0(standard glass) 12 2.8 3.2 3.7

16 2.7 3.1 3.60.2 6 2.8 3.1 3.6

DOUBLE (low-E glass) 12 2.3 2.6 3.1(air filled) 16 2.1 2.4 2.9

0.1 6 2.7 3.0 3.5(soft low-E glass) 12 2.1 2.4 2.9

16 2.0 2.3 2.80.89 6 2.9 3.3 3.8

(standard glass) 12 2.7 3.1 3.616 2.6 3.0 3.5

0.2 6 2.5 2.9 3.4DOUBLE (low-E glass) 12 2.1 2.4 2.9(argon filled 16 2.0 2.3 2.8– 90% argon, 0.1 6 2.4 2.7 3.210% air) (soft low-E glass) 12 1.9 2.2 2.7

16 1.8 2.1 2.60.89 6 2.4 2.7 3.2

(standard glass) 12 2.1 2.4 2.9TRIPLE 0.2 6 2.1 2.4 2.9(air filled) (low-E glass) 12 1.7 2.0 2.5

0.1 6 2.0 2.3 2.8(soft low-E glass) 12 1.6 1.8 2.3

0.89 6 2.2 2.6 3.1(standard glass) 12 2.0 2.3 2.8

TRIPLE 0.2 6 1.9 2.2 2.7(argon filled) (low-E glass) 12 1.6 1.8 2.3

0.1 6 1.8 2.0 2.5(soft low-E glass) 12 1.5 1.7 2.2

ROOFLIGHTS(increase on equivalent window U-values)Single + 0.3 + 0.3 + 0.7double or triple + 0.2 + 0.2 + 0.7

DOORSSolid Wooden 3.0 -- --Part glazed Calculate overall door resistance from resistance of individual parts

a proportional basis.U-value is inverse of resistance.

4949

GENERAL

C.1 This Appendix presents the procedure forthe calculation of the Heat Energy Rating (HER) andMaximum Permissable Heat Energy Rating (MPHER)of a dwelling. The Heat Energy Rating is a measure ofthe annual energy requirements of the dwelling forspace heating and domestic hot water forstandardised conditions. It takes account of

• energy requirements associated with heat lossthrough the fabric, including loss at thermalbridges,

• energy requirements associated with airinfiltration and ventilation,

• energy requirements associated with theprovision of domestic hot water,

• energy inputs associated with solar gain,• energy inputs associated with occupancy

including the use of energy-using appliances,• the heating system responsiveness to demand

and it’s degree of control.

The HER and MPHER are expressed in terms ofenergy requirements per unit floor area of thedwelling per annum (W/m2/yr.).

C.2 The procedure is presented in the form of aworksheet accompanied by a number of Tables. Thisworksheet is appropriate for most situations.However, for particular situations such as buildingsusing active solar systems for space or water heating,some forms of passive solar systems or othersystems making use of renewable energy sources,additional calculations may be necessary.

C.3 Boxes in which data in relation to thedwelling are to be entered are shown unshaded;boxes in which the results of calculations involvingpreviously entered data are to be placed are shownshaded. Where there is no relevant data, boxesshould be left blank.

OVERALL DWELLING DIMENSIONS

C.4 The dwelling is considered in terms ofindividual floors up to a maximum of three. For eachfloor, enter the floor area in Box (1), (2) and (3), asappropriate. For the ground or lowest floor, theaverage storey height is taken between floor surfaceand ceiling surface. For other floors, the average

storey height is taken between the ceiling surface ofthe storey below and the the ceiling surface of thestorey in question. The average storey height isentered in Box (4), (5) and (6) as appropriate. Forany part of the building not included in the one, twoor three storey categories, enter the total floor areain Box (10) and the total volume in Box (11). TheseBoxes may also be used to enter areas and/orvolumes of small parts of the dwelling which may notbe conveniently included in the calculation of floorarea, average storey height and volume, e.g. baywindows, dormer windows and other protrudingsections of varying height. Unheated areas andconservatories, other than those treated as integralto the building in accordance with Paragraph 1.1.3,should not be included.

C.5 The basis for calculating areas and volumes isas given in Paragraph 0.15.

C.6 Wall and roof areas are net areas excludingany windows, doors or rooflights. Window, doorand rooflight areas are the total areas of the relevantopenings, including frames.

RATE OF HEAT LOSS THROUGH THEBUILDING FABRIC

C.7 U-values are derived in accordance withParagraphs 0.10 and 0.12 and Appendices A and B.In general, the Worksheet allows for two types ofeach element. Where there are more than twotypes, the Areas and Rate of Heat Loss of theadditional elements may be calculated outside of theWorksheet, grossed up, and the combined resultsentered in the “Other” category.

Heat loss due to thermal bridging should be enteredin Box 31. This may be derived by calculation asoutlined in Appendix D. Alternatively, wherestandard details as described in Par. 1.5.2 andassociated references are used, heat loss at thermalbridges should be taken as 15% of heat loss throughfabric elements.

RATE OF HEAT LOSS DUE TOVENTILATION

C.8 The Effective Air Change Rate is made up ofthree parts - a basic air change rate associated withthe particular type of construction, additional air

Appendix C Heat Energy Rating:Standard Calculation Method

50

changes associated with particular elements such aschimneys, flues, vents, fans, lobbies, etc., and anallowance for occupant controlled ventilation basedon the sum of the basic and additional air changes.

C.9 The Basic Air Change Rate represents airleakage through the building shell including all airinfiltration through cracks and unsealed gaps and isexpressed in terms of air changes per hour. Itincludes infiltration at opening sections of windowsand doors and at any fully closeable vents provided.Specific permanent openings of various kinds are notincluded in these figures. The basic air change ratedepends on the type of construction and is adjustedin relation to the number of stories and the type ofground floor provided. Good quality construction,including compliance with Paragraph 1.6, is assumed.

When considering “type of construction”, traditionalmasonry construction should generally be classifiedas “standard construction”. “Sealed Construction”should only be assumed where a continuous airinfiltration barrier with sealed joints and specificmeasures to ensure sealing at all openings,penetrations by pipes, cables, etc. are incorporatedin the construction.

C.10 Large Flue means a flue with a large diameter(200 mm or greater) and large opening at the base,e.g. flue serving solid fuel open fire with or withoutboiler or an open coal effect gas fire.

Small Flue includes all open flues serving closedappliances which draw air from the heated area, e.g.flues to closed solid fuel appliances, gas fires and oilor gas fired boilers within the heated area. Balancedflues are not included.

Permanent Vent means a ventilation opening notdesigned to be fully closeable. A typical traditionalwall vent would be classified as “large”. For ventsthat are partly closeable, the area referred to is thearea of opening when closed as far as possible. Suchvents will generally be classified as “small”. Nospecific ventilation allowance is made for ventilationopenings which are capable of being fully closed.

A Passive Vent, as described in BRE InformationPaper IP13/94, is a near vertical duct running from akitchen, utility room or bathroom ceiling to aterminal above the roof, designed to have a similar

effect as an intermittently operated fan. Extract fansand cooker hoods should be included when derivingthe number of fans. Any fans forming part of awhole-dwelling mechanical ventilation system shouldnot be included in this category.

Houses with such systems must be treatedseparately. (See Paragraph C.14).

C.11 Where a fan pressurisation test on a dwellingis carried out, this provides a more accurate estimateof likely air change rates. The results of this testshould be used with the air change rate estimated bydividing the infiltration rate at 50 Pascals by 20. Theresult should be entered in Box (35). The additionalair changes due to flues, vents, fans etc. should beestimated as set out in the worksheet but includingonly those openings specifically sealed during thepressurisation test.

C.12 In deciding on the number of sides sheltered,account should be taken of existing buildings andplanting and of proposed buildings in the samedevelopment as the dwelling in question. Proposedplanting should be ignored.

A side should be considered sheltered if:

• the obstacle providing shelter is at least as high asthe ceiling of the uppermost storey of thedwelling,

• the distance between the obstacle and the otherdwelling is less than five times the height of theobstacle,

• the angle between the line of the obstacle andthe side of the dwelling is not greater than 450

and• the width of the obstacle is such that at least

two-thirds of the side of the dwelling falls withinthe triangle created by the line of the obstacleand lines drawn from the end of the obstacle at700 to the line of the obstacle.

Unless the location of the dwelling is sufficiently welldefined that the number of sides sheltered {Box(45)} can be clearly specified, the following should beassumed:

• for dwellings in build-up areas or forming part ofa larger development assume two sides sheltered(shading factor of 0.85);

51

• for dwellings in open countryside or distant fromother buildings of similar or greater size, assumeno side sheltered (shading factor of 1.00).

C.13 The Effective Air Change Rate allows foroccupant controlled ventilation. The minimumeffective air change rate is assumed to be 0.5 airchanges per hour, while at air change rates above 1.0air changes per hour, additional air changes due tooccupants is assumed to be negligible.

C.14 Where full mechanical ventilation, with orwithout heat recovery, is installed, the rate of heatloss due to ventilation should be calculatedseparately based on the characteristics of thedwelling construction and the system installed. Thevalue so derived should be entered in Box (49) andthe calculations on which it is based provided on aseparate sheet.

WATER HEATING

C.15 The estimate for the energy content ofheated water is taken from Table 29 and is basedon the floor area of the dwelling as entered inBox (12).

C.16 Three types of losses are considered -Distribution Losses, Storage Losses and PrimaryCircuit Losses. Values for each are given in Tables 29,30 and 31 respectively. For stored water systemsusing an indirect cylinder, with water heated via aheating coil and primary circuit by a boiler at somedistance from the cylinder, and with a number of hotwater outlets served from the storage cylinder, allthree types of losses apply. For stored watersystems heated by an electric immersion heater orequivalent, there are no Primary Circuit Losses. Forinstantaneous water heating systems with a numberof hot water outlets served from a single boiler, e.g.gas multipoint heater or combi boiler, onlydistribution losses apply. None of the three types oflosses apply to single point heaters, without storage,located at point of use.

SOLAR AND OTHER ENERGY GAINS

C.17 The solar gain data given in Table 32 aretypical figures for Ireland for the orientations given.The areas of windows and other glazed areas shouldbe entered for each orientation when known. The

areas entered should be inclusive of framing. Wherethe orientation of the dwelling is not fixed, the totalarea should be shared equally between East andWest orientations. This approach may also beadopted where a number of identical dwellings arebeing constructed with varying orientations and it iswished to avoid doing separate calculations for eachdwelling.

C.18 Gains from water heating are calculatedbased on the figures already derived for the energycontent of heated water and the associated losses.

C.19 Gains from other energy uses are given inTable 33 as a function of floor area. These aretypical figures.

C.20 The effectiveness of gains in contributing tothe space heat requirements of the dwelling dependson the ratio of the rate of gross heat gains to that ofheat losses - given as Specific Heat Loss [Box (50)].This ratio is calculated and entered in Box (73).Based on this the appropriate utilisation factor isfound in Table 34 and entered in Box (74). The totalgains already calculated [Box (72)] are multiplied bythe utilisation factor to give Useful Gains [Box (75)].This is divided by the rate of heat loss to give theaverage temperature rise from gains [Box (76)].

SPACE HEATING

C.21 The mean internal temperature given inTable 35 is based on the heating requirements of atypical household with the dwelling heated morningand evening and with a higher temperaturemaintained in the living zone (assumed to be one-third of the floor area) than in the remainder of thedwelling. For dwellings insulated to the standardsrequired by Part L, the main factors affecting averagetemperatures over the heating season are theresponsiveness of the heating system and the type ofheating system controls used. In Table 35 four typesof heating systems in terms of responsiveness areidentified and three levels of heating system control.

C.22 The mean internal temperature is achievedpartly through heat input from solar and other gainsand partly through heat input from the space heatingsystem provided. The temperature rise from gains issubtracted from the mean internal temperature togive the Base Temperature which must be met by the

52

space heating system [Box (78)].

C.23 Degree-days is a measure of the extent towhich the external temperature falls below aspecified base temperature taking account of bothtemperature and time aspects. Typical degree-daysfor Ireland are given in Table 36 for a range of basetemperatures. The appropriate value is entered inBox (79).

C.24 The energy to meet space heating demand iscalculated by multiplying degree-days [Box (79)] bythe specific heat loss [Box (50)] and by a conversionfactor which converts the result to kWh/yr. Theresult is entered in Box (80).

C.25 As with water heating there may also belosses associated with space heating. The majority ofspace heating systems do not involve storage andthus there are no equivalents of the storage andprimary circuit losses which can occur in waterheating. Further it is assumed that losses fromdistribution pipes and ducts contribute to thespecified heat energy requirement when these pipesand ducts are located within the heated space. Themain distribution losses are therefore thoseassociated with pipe and ductwork located outsidethe heated space - generally in the void underneath atimber ground floor, embedded in a solid concreteground floor or in the attic space. Table 37 givestypical annual losses as a function of the dwelling planarea. The appropriate figure should be entered inBox (81).

HEAT ENERGY RATING (HER)

C.26 The HER is specified in kWh/m2/yr and isderived by dividing the energy for space and waterheating for the dwelling [Box (84)] by the dwellingfloor area [Box (12)]. Compliance is assessed bycomparing the calculated HER with the MaximumPermitted Heat Energy Rating [MPHER] as set out inTable 4 of this TGD.

53

DWELLINGS - ASSESSMENT OF COMPLIANCE ON BASIS OF HEAT ENERGY RATING

STANDARD CALCULATION WORKSHEET

Table 29: Domestic hot water - Energycontent and distribution losses

55

Floor Area Hot Water Distribution(m2) Energy Use Loss

(kWh/yr) (kWh/yr)___________________________________________

30 695 11640 842 14050 984 16460 1123 18770 1256 20980 1386 23190 1511 252

100 1633 272110 1749 292120 1862 311130 1970 329140 2075 346150 2174 363160 2270 379170 2361 394180 2449 409190 2531 422200 2610 436

Note: The energy content of hot water used anddistribution losses may be estimated byinterpolation in the above Table. For Floor Areasoutside the range given, they may be calculated asfollows:

Hot water usage = 425N + 230 (kWh)Distribution Loss = 71N + 38 (kWh)where N = 0.038F - 0.00005F2 (for F < = 300 m2)

N = 7 (for F>300 m2)And F = floor area (m2).

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Table 30 Hot water cylinder storage loss factor (kWh/yr/litre)

Table 31 Primary circuit losses (kWh/yr)

Energy Source Dwelling Floor area (m2)

> 100 m2 75 to 100 m2 50 to 75m2 < 50m2

Electric Immersion heater 0 0 0 0

Boiler with uninsulated primary pipework 611 550 428 306

Boiler with insulated primary pipework 361 325 253 181

NOTE 1: See par. 3.3.1, for insulation of pipes carrying hot water.

NOTE 2: The factors given for floor areas greater than 100 m2 should be used in all cases where the hot water system is not provided with separate time control.

Cylinder insulation Dwelling Floor area (m2)

Type Thickness (mm) > 100 m2 75 to 100 m2 50 to 75m2 < 50m2

Foam 25 4.36 3.92 3.05 2.1838 2.89 2.60 2.02 1.4550 2.17 1.95 1.52 1.0980 1.36 1.22 0.95 0.68

100 1.08 0.97 0.76 0.54150 0.72 0.65 0.50 0.36

Jacket 80 4.36 3.92 3.05 2.18100 3.50 3.15 2.45 1.75150 2.33 2.10 1.63 1.17

NOTE 1: See par. 1.8.2 for insulation of hot water cylinders.

NOTE 2: The factors given for floor areas greater than 100 m2 should be used in all cases where the hot watersystem is not provided with separate time control.

57

Table 32 Solar flux through glazing (W/m2)

Glazing Orientation

Glazing Type Horizontal Vertical

North NE/NW E.W SE/SW South

Single glazed 34 10 12 20 29 34Double glazed 28 8 9 16 24 28Double glazed with low - E coating 25 7 9 14 22 25Triple glazed 24 7 8 13 20 24

NOTE 1: For a rooflight in a roof with pitch 5° to 70°, use the value under "North" for orientations within 30° of north and the value under "Horizontal” for all other orientations.

For a pitch of less than 5°, treat as horizontal.

For a pitch of more than 10°, treat as vertical.

NOTE 2: The data above relates to an average degree of overshading. The following correction factors apply where the degree of overshading differs from this.

Overshading % sky blocked Shading correctionby obstacles factor

Heavy >80 0.4Above average 60-80 0.7Average 20-60 1.0Very little <20 1.3

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Table 33 Lighting, appliances, cooking and metabolic gains

Floor Area Gains Floor Area Gains(m2) (W) (m2) (W)

30 198 120 60240 246 130 64350 293 140 68460 340 150 72370 385 160 76280 430 170 80090 474 180 838

100 518 190 874110 560 200 910

NOTE 1: Lighting, appliances, cooking and metabolic gains may be estimated by interpolation in the above Table.

For Floor Areas outside the range given these may be calculated as follows:Gains = 50 + 2.2F + 75N (W)N = 0.038F - 0.00005F2 (For F < 300 m2)N = 7 (for F> 300m2) and F = floor area (m2)

NOTE 2: When the following equipment is present, the associated gains should be added to those derived from the above Table:

central heating pump - 10Wwarm air heating system fan - 10Wmechanical ventilation system - 25W

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Table 34 Utilisation factor as a function ofHeat Gain/Loss Ratio (G/L)

Table 35 Mean internal temperature ofdwelling (K)

Heating System Control CategoryResponsiveness 1 2 3

1 18.45 18.07 17.812 18.90 18.52 18.263 19.35 18.97 18.714 19.80 19.41 19.15

Notes:

Responsiveness Categories

1. Standard gas or oil-fired fired radiator orwarm-air systems; gas, oil or direct electricroom heater systems.

2. Solid-fuel fired radiator based systems withboiler external to heated space; Electricaire orequivalent warm-air systems.

3. Solid-fuel based systems with boiler withinheated space. Fan-assisted electric storageheaters.

4. Electric storage heater systems (other than fan-assisted); underfloor heating.

Control Categories

1. Basic control e.g. single room thermostat plustimer.

2. Thermostatic radiator valve control, or similar.3. Full time and temperature zone control (at

least two zones).

G/L Utilisation G/L Utilisation factor factor

___________________________________________1 1.00 16 0.682 1.00 17 0.653 1.00 18 0.634 0.99 19 0.615 0.97 20 0.596 0.95 21 0.587 0.92 22 0.568 0.89 23 0.549 0.86 24 0.53

10 0.83 25 0.5111 0.81 30 0.4512 0.78 35 0.4013 0.75 40 0.3614 0.72 45 0.3315 0.70 50 0.30

___________________________________________

NOTE: Util isation factors for intermediateGain/Loss ratios may be estimated by interpolationin the above Table.Alternatively, the util isation factor may becalculated by the formula:Utilisation factor = 1 - exp(-18/(G/L)).

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Table 36 Degree-days as a function of basetemperature

Base Degree Base DegreeTemperature Days Temperature Days(°C) (°C)___________________________________________

6 287 14 15837 394 15 17908 521 16 19999 665 17 2209

10 835 18 242011 998 19 263212 1185 20 284513 1381

___________________________________________

Note: Degree days for intermediate base temperaturesmay be estimated by interpolation in the above Table.

Table 37 Space heating distribution losses(kWh/yr)

Ground Floor Distribution Loss (kWh/yr)Area (m2)___________________________________________

Pipe/Duct in Pipe/Duct floor void embeddedor attic in ground floor

___________________________________________

40 220 11050 240 12075 290 145

100 330 165125 370 185150 410 205175 440 220200 470 235250 530 265300 580 290

Table 38 Additional energy consumptionassociated with heating andventilation equipment

Equipment Energy Consumption

(kWh/yr)___________________________________________

Central heating pump 120Warm Air heating system fan 150Mechanical ventilation 300

61

Appendix D Thermal Bridging

GENERAL

D.1 This Appendix deals with the assessment ofdiscreet thermal bridging, e.g. at junctions andaround openings such as doors and windows. It givesguidance on

• avoidance of mould growth and surfacecondensation, and

• limiting factors governing additional the heatlosses.

The guidance is based on “BRE IP 17/01 Assessingthe effects of thermal bridging at junctions andaround openings” and can be used to demonstrateadequate provision to limit thermal bridging whenthe guidance in relation to appropriate detailing ofsills, jambs, lintels, junctions between elements andother potential thermal bridges contained inParagraphs 1.5.2 and 1.5.3, and associated referencedocuments, is not followed.

CALCULATION PROCEDURES

D.2 Details should be assessed in accordance withthe methods described in I.S. EN ISO 10211 Parts 1and 2. This assessment should establish thetemperature factor (fRsi) and linear thermaltransmittance (ψ).

The temperature factor (fRsi) is defined as follows:fRsi = (Tsi – Te) / (Ti – Te)

where:Tsi = minimum internal surface

temperature,Te = external temperature, andTi = internal temperature.

The linear thermal transmittance (ψ) is thecalculated correction factor for heat loss per unitlength of a linear thermal bridge.

MOULD GROWTH AND SURFACECONDENSATION

D.3 For dwellings, the value of fRsi should be greaterthan or equal to 0.75, so as to avoid the risk ofmould growth and surface condensation. For three-dimensional corners of ground floors this value maybe reduced to 0.70, for all points within 10 mm ofthe point of lowest fRsi.

ADDITIONAL HEAT LOSS

D.4 The additional heat loss associated withthermal bridges should be limited to less than 16% ofthe total calculated heat loss through the planebuilding elements when the Elemental Heat Lossmethod is used to show compliance. Where eitherthe Overall Heat Loss method or the Heat EnergyRating method is used to show compliance, anyadditional heat loss above this level should beexplicitly taken into account in calculating the OverallHeat Loss or the Heat Energy Rating as the case maybe.

D.5 Where the guidance given in Paragraphs 1.5.2and 1.5.3 and associated references is followed orwhere the linear thermal transmittance of allthermal bridges does not exceed those set out inTable 39, it can be assumed that the additional heatloss associated with thermal bridging is not excessiveand no further calculation is necessary. Where thelinear thermal transmittances of some thermalbridges exceed those set out in Table 39, the overalladditional heat loss associated with thermal bridgingshould be established and allowed for in assessingcompliance, as outlined above. In this assessment,any detail that complies with the guidance inParagraphs 1.5.2 and 1.5.3 and associated referencescan be assumed to have the value of ψ set out inTable 39. Alternatively the detail can be assessed andthe calculated value used in the calculation of overallheat loss due to thermal bridging.

62

Detail in external Maximum value element/junction with of ψ (W/mK)external element

Windows/doorsMetal box lintel 0.30Other lintel 0.21Sills/jambs 0.06Junctions with external element Ground floor, intermediatefloor, Party wall 0.16Eaves (ceiling level) 0.06Gable (ceiling level) 0.24

Note: For party walls and intermediate floorsbetween dwellings, half of the ψ - value should be

applied to each dwelling when assessing theadditional heat loss associated with bridging.

Table 39 Maximum values of linearthermal transmittance (ψ) forselected locations

63

Appendix E Limitation of Heat Loss through Building Fabric

E.l The following example il lustrates theapplication of the three methods of demonstratingthe efficient limitation of heat loss through thebuilding fabric.

The example relates to a semi-detached house.

It is assumed that the construction details at thermalbridges are in accordance with those referred to inPar. 1.5.2. It is also assumed that the constructionscomply with the guidance regarding thermal bridgingat edges of floors (paragraph 1.5.3) and limitation ofair infiltration (paragraph 1.6).

Example E.1: Semi-Detached House

It is proposed to construct a semi-detached twostorey house with the following dimensional andconstruction characteristics.

Dimensions: Width - 6 m (internal) Depth - 8 m (one side only

exposed, adjoining houseattached on other side)

Height - 5.1 m (2.4 metres floor toceiling height, 300 mmfirst Floor zone).

Door and Window Openings:

Front - 11.0 m2 (including1.8 m2 front door)

Rear - 9.6 m2 (including1.8 m2 rear door)

Side - 1.5 m2

Total - 22.1 m2 (23% of floorarea).

Construction:

Roof: Pitched tiled roof,insulation laid on atticfloor, part between joistsand part over Joists.

Walls: Cavity wall (denseconcrete blocks) renderedexternally, dry-lined

internally with partial fillinsulation in the cavity and50 mm cavity retained.Any additional insulationto be provided as internallining between battens.

Floor: Concrete slab-on-groundfloor with insulation underslab.

The following are the assumed thermal conductivitiesof the insulation materials used:

roof insulation 0.04 W/m2Kwall insulation 0.037 W/m2Kfloor insulation 0.037 W/m2K .

ELEMENTAL HEAT LOSS METHOD

This is the easiest method to apply but provides littleflexibility. Table 1 gives the required U-values.

The required thickness of insulation for roof andwalls may be calculated by the method specified inAppendix A, or estimated using the appropriateTables from Appendix B. Based on Tables 6 and 16,the required thickness of attic and wall insulation are250 mm and 110 mm respectively. The requiredthickness of insulation in the ground floor dependson the ratio of exposed perimeter to floor area. This

Diagram 34 Para. F.2 Semi-detached house

2.4 m

2.4 m0.3 m

6 m8 m

64

ratio is 20/48, or 0.42. Using Table 23 and assumingan insulation thermal conductivity of 0.037 W/mK,the thickness of floor insulation required is 93 mm.

Table 2 indicates that the required average U-valueof windows, doors and rooflights (at 23% of floorarea) is 2.37 W/m2K. The following table presentsone combination that meets this requirement:

Other combinations can also be used to satisfy thisrequirement. However, it is important to check forcompliance in relation to specific doors and windowsproposed. Not all combinations comply. Forexample, a combination of two solid woodenexternal doors and double-glazed wood or PVCwindows using a 12 mm gap and standard low-e glass(emmissivity = 0.2) would not comply in this case.

OVERALL HEAT LOSS METHOD

This method provides greater flexibility for thedesigner allowing compensation for a reduction ininsulation provision in one element by an increase inprovision in another element. It also provides greaterflexibility in relation to the areas and types of glazingprovided. Use of this method requires calculation ofthe total heat loss area (At), the building volume (V)and the average U-value of the heat loss elements(Uav). The calculation of Uav requires themultiplication of area and U-value for each element,summing the product calculated and dividing the sumby the total area of all heat loss elements. Thecalculated Uav is then compared to the maximumaverage U-value (Um) for this building, which is

specified in Table 3.

While the U-values of roofs, walls and ground floorscan be relaxed (relative to the U-values specified orthe Elemental method) to the values set out inParagraph 1.3.2., it will generally be necessary tocompensate for a reduction in insulation in oneelement by increased insulation elsewhere. It willrarely be possible to relax all U-values to the extentallowed by Paragraph 1.3.2. While some reduction inwindow area may facilitate trade-off, glazed areasshould not be so small as to affect the adequacy ofdaylighting.

For the house under consideration, the constructionmay be varied by using 60 mm insulation withthermal conductivity of 0.025 W/mK in the cavitywith no extra insulation behind the drylining. Thisgives a U-value of 0.33 W/m2K for the walls, which isacceptable provided the maximum average U-value(Um) is not exceeded. To achieve this some increasein insulation elsewhere is required. For example, theattic insulation could be increased to 300 mm givinga U-value of 0.13 W/m2K, and the air gap in theglazing also increased to 16 mm giving a U-value forthe windows of 2.0 W/m2K. In addition the use ofhalf glazed wooden doors with double glazing usingstandard low-e glass and 12 mm gap between panesgives a door U-value of 2.65 W/m2K. Taking all thesechanges into account, Uav can be calculated asfollows:

Heat loss Area U-value Area x Element (m2) (W/m2K) U-value

(W/K)___________________________________________Roof 48.00 0.13 6.24

Wall 79.90 0.33 26.37

Floor 48.00 0.25 12.00

Windows (double 18.50 2.00 37.00glazed, soft low-E glass, 16 mm gap, wooden frame)

Doors 3.60 2.65 9.54

198.00 - 91.15

Area U-value A x UType (m2)

Doors Solid Wooden 3.6 3.0 10.8

Windows Softwood frame, 18.5 2.1 38.85Double glazed, 12mm gap, Soft low-e glass

Totals 22.1 - 49.65

Average 49.65/22.1 - 2.25 -U-value

65

Uav = Total AU / At = 91.15/198 = 0.46W/m2K

Building Volume (V) = 244.80m3

At / V = 198.00/244.80 = 0.81 (m-1)Um (from Table 3) = 0.47 W/m2K.

The proposed construction is acceptable as Uav isnot greater than Um.

HEAT ENERGY RATING METHOD

This method provides additional flexibility for thedesigner relative to the Overall Heat Loss method.The required calculation is described in Appendix C.The same requirement as for the Overall Heat Lossmethod applies in relation to the U-values of roofs,walls and ground floors.

The calculation of the Heat Energy Rating requiresadditional information regarding the house details asfollows:

no. of chimneys/flues 1

no.of permanent vents(small) 6

no. of fans 2

draught lobbies to provide draught lobby toexternal doors front

degree of shelter 2 sides sheltered

type of heating system standard gas-fired radiator central heating system

heating system control thermostatic radiator valves

water heating system combined space and hot water system using 120 litre storage cylinder with 50mm factory applied foaminsulation and uninsulated primary circuit and distribution pipes.

As standard construction details are used atlocations of possible thermal bridges, the calculatedHeat Energy Rating (HER) includes an estimate ofheat loss at thermal bridges of 15% of the lossthrough the external fabric elements. The followingassessment indicates the type of flexibility that canbe achieved by this method. For this assessment, it isassumed that, in addition to providing draught lobbyto front door, the window area is redistributed toprovide 12.5 m2 south facing and the remaining 6 m2

north facing. The following construction is proposed:

- Roof U-value 0.16 W/m2K (250 mm insulation (thermal conductivity 0.04 W/mK)laid between and over joists (Table 6))

- Wall U-value 0.33 W/m2K (60mm insulation (thermal conductivity 0.025 W/mK) (Table 14))

- Floor U-value 0.25 W/m2K (93 mm insulation (thermal conductivity 0.037 W/mK) (Table 23))

- Window U-value 2.30 W/m2K (Double glazed, Low-E glass, 12mm gap, softwood frames (Table28))

- Door U-value 3.00 W/m2K (solid timber doors (Table 28))

The calculation shows that the house has a HER of91.70 kWh/m2/yr. This is less than the calculatedMPHER of 92.79 kWh/m2/yr. The proposedconstruction is therefore acceptable.

66

Example E1 - HEAT ENERGY RATING CALCULATION

68

Standards and Other References

Standards referred to:I.S. 161: 1975 Copper direct cylinders for domesticpurposes.I.S. 325: 1986 Part 1: Structural use of unreinforcedmasonry.I.S. EN 832: 1999 Thermal Performance of Buildings– Calculation of Energy Use for Heating – ResidentialBuildings.I.S. EN ISO 6946: 1997 Building components andbuilding elements –Thermal resistance and thermaltransmittance – Calculation method (ISO 6946:1996).I.S. EN ISO 8990: 1997 Thermal insulation –Determination of steady-state thermal transmissionproperties – Calibrated hot box.I.S. EN ISO 10077-1: 2000 Thermal performance ofwindows, doors and shutters – Calculation ofthermal transmittance – Part 1: simplified method(ISO 10077-1: 2000).I.S. EN 10077-2: 2000 Thermal performance ofwindows, doors and shutters – Calculation ofthermal transmittance – Part 1: Numerical methodsfor frames (ISO 10077-2: 2000).I.S. EN ISO 10211-1: 1996 Thermal bridges inbuilding construction – heat flows and surfacetemperatures. Part 1 general calculation methods.I.S. EN ISO 10211-1: 2001 Thermal bridges inbuilding construction – heat flows and surfacetemperatures. Part 2 linear thermal bridges I.S. EN IS0 10211-2:2001 Thermal bridge in buildingconstruction - heat flows and surface temperature.Part 2 linear thermal bridgesI.S. EN 12524: 2000 Building materials and products– Hygrothermal properties – Tabulated design values.I.S. EN ISO 12567-1: 2001 Thermal performance ofwindows and doors – Determination of thermaltransmittance by hot box method – Part 1:Complete windows and doors (ISO 12567-1: 2000).I.S. EN 12664: 2001 Thermal performance of buildingmaterials and products – Determination of thermalresistance by means of guarded hot plate and heatflow meters method – Dry and moist products oflow and medium thermal resistance.I.S. EN 12667: 2000 Thermal performance of buildingmaterials and products – Determination of thermalresistance by means of guarded hot plate and heatflow meters method – Products of high and mediumthermal resistance.I.S. EN 12939: 2001 Thermal performance of buildingmaterials and products – Determination of thermalresistance by means of guarded hot plate and heat

flow meters method – Thick products of high andmedium thermal resistance. I.S. EN ISO 13789: 2000 Thermal Performance ofBuildings – Transmission Heat Loss Coefficient –Calculation Method (ISO 13789: 1999).I.S. EN ISO 13370: 1999 Thermal performance ofbuildings – Heat transfer via the ground – Calculationmethods (ISO 13370: 1998).BS 747: 2000 Reinforced bitumen sheets for roofing– Specification.BS 1566 Copper indirect cylinders for domesticpurposes Part 1: 1984 Double feed indirect cylinders.BS 5422 : 2001 Method for specifying thermalinsulating materials on pipes, ductwork andequipment (in the temperature range - 400C to +7000C).BS 5449: 1990 Specification for forced circulation hotwater central heating systems for domesticpurposes.BS 5864: 1989 Specification for installation indomestic premises of gas-fired ducted air-heaters ofrated output not exceeding 60 kW.BS 8206: Part 2: 1992 Lighting for buildings Part 2.Code of practice for daylighting.

Other Publications referred to:BRE Report BR262, Thermal Insulation : avoidingrisks, BRE 2001CIBSE Guide, Volume A: Design Data - Section A3:Thermal Properties of Buildings and Components,1999HOMEBOND “Right on Site” Issue No. 28, BuildingRegulations 2002 - Conservation of Fuel and Energy- Dwellings.Architectural Heritage Protection Guidelines forPlanning Authorities, Department of theEnvironment , Heritage and Local Government 2004.BRE Digest 465 U-values for light steel frameconstruction, BRE ,2002.BRE Report 443, Conventions for the Calculation ofU-values, BRE, 2002.BRE Information Paper 17/01 Assessing the effects ofthermal bridging at junctions and around openings,BRE, 2001.Limiting thermal bridging and air leakage: Robustconstruction details for dwellings and similarbuildings, DEFRA and DTLR, The Stationery Office,London, 2002.

technical guidance document l conservation of fuel and

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