\ ...... .J,")l/ \) ~ ,,'I ( /I

DESIGN NOTE

J

, oY J.

-f (

" (.'1 v

rJ ~ ) ',V (J e /: ' I, 'J. \ ,:-- ,

Published by the Brick Development Association" I ~ )I , )\

') , .) , r r / ( J V\ ,\ / C

) I , '\ ' t f, .RESIS~ING , R,Al~j P~~ETf..A ~I~N

J.../) .' ) , \'( I

(

i )if

t If/

CONTENTS

PAGE

INTRODUCTION

SCOPE

... 3

3

DESIGN PROCEDURE ASSESS AND SELECT 4

ASSESSING EXPOSURE FOR SPECIFIC LOCATIONS .... 4

67

............................... . ........ ................ 7.. 8

88

........... ........ . 9. 10.. 12

...... ......... ............ ............... .. 13

SELECTION OFMATERIALS AND CONSTRUCTION TO RESIST WINDDRIVEN RAIN1 TYpe of brick . .2 Mortar composition .3 Thickness of leaf4 Cavity walls .5 Width of air space within any cavity6 Mortar joint, profile and finish .7 Cavity insulation "'8 Architect ural features and local practice .9 Applied external surface finishes ..10 Quality of workmanship to be achieved on site

DAMP PROOF COURSES AND CAVITY TRAYS...............14

.......... 14... 15... 15

................................................................ 15....... .. 15

GeneralPerfonnance .[unctions ..Continu ity and support ..Resisting rising damp

Immediately above ground levelBelow ground level .

Controlling downward movement of wat erCavity walls .... 16Overopenings . 16Arches .. 16Stop ends .. .. .... 17Weepholes .. 17

Requirements for damp proof cou rses and cavity trays for specific parts of buildingsAt jambs to openings .. .. 18Sills .. 19Requirements for additional cavity trayswith cavityinsulation 19External wall becoming an internal wall .. . 20Parapets .. 20Copings and cappings 21Chimneys 22Structural frames . . . . 22Flashings and weatherings .. 23

........................ 23

................ ..... ..... ............... ............. 23

....................................... 24

710

.......... 15

.. 5Classification of exposureto local winddriven rain , .Minimum thickness of solid brickwork walls, with and without rendering,to resistrain penetration in various categories of exposure..Thermalinsulationmaterials forusein cavity insulated wallsSummary of materialsusedfordamp proofcourses and cavity trays

Table 3Table 4

CONCLUSION

REFERENCES

ACKNOWLEDGEMENTS

TABLESTable 1Table 2

Brickwork has been a dependable form ofconstruction for weather resistant walls forhundreds of years, but conventional bricks andmortarsarenot themselves waterproof.

Moisture may penetrate brickwork by diffusingthroughmicroscopic voidsin the materials, or bypercolating or flowing into and through hairline ormore noticeable cracks in the fabric. Theeffectiveness ofa solidbrick wall in resistingpenetration by wind-driven rain is in directproportion to wall thickness. Traditionally, forbuildings in locationswhere greater severity ofexposureto wind-driven rain is experienced. thickerwallsareused compared with those for buildings inmore sheltered situations.

In the mid-nineteenth century therewasconsiderableinterest in the construction of low-costhousingforworkers. Economy ofmaterial wassought, but thinner walls equated with reduced

The resistance of masonry to wind-dnven raininvolves assess ing performance relative toanticipated exposure, as opposed to achieving anabsolute condition of its being waterproof.Thispublication examines and comments on the relativesignificance of the various factors that need to beconsideredwhen assessing exposureand thenspecifying an appropriate wall construction for anyparticular application.

Solid brickwallconstruction is considered andalso the protection offered by rendered finishes isacknowledged, but the publication concentrates onthe deta ildesign and specificat ion of cavtty walling

INTRODUCTION

resistance to rain penetration. This shortcoming ofsolid walls led to expe rimentation with hollow wallconstruction by the use of part icular bondingarrangements such as rat-trap bond, Silverlockbond and Dearne's bond and also by thedevelopment of patent hollow bricks. However, themost significant development was the introductionof double-leaf cavity walling. By the twent iethcentury this technique had become esta blished andby the' 930's it was widely used in housing.

The design of the cavity wall accepts that solidmasonry subjected to wind-driven rain will not beabsol ute ly waterproof but is capab le of providingsubstantial resistance to penetration. To divert thepassage of any moisture that may pass through theexternalleaf of the wall the cavity is introduced todrain it down and out again to the exterior.This ensures that waterwillnot penetrateto theinternal leaf of the wall causing dam p cond itionswithin the building.

SCOPE

with an outer-leaf of fairface brickwork. The effectsof incorporating thermal insulating materials withinthe cavity arealso examined.

As damp proof courses and cavity trays areessential components incorrectly detailed cavitywall design, guidance is included on theirspecification and installation.

With an understanding of the constra ints andopportunities that attend differences inseverityofexposureand in the performance of diverseconstruction features, a designercan exploit thegreat choice offered by brickwork to provideeffective protection and attractive appearance.

DESIGN PROCEDURE - ASSESS AND SELECT

Because the performance of a specific form ofwall constructionhasbeen satisfactory in aparticular locality it must not be assumed that itwill be equally suitable in other regions. Design andspecification assumingworstcaseconditionsmaybe considered to provide notionaluniversalapplications, but for the majority of buildings on themajority of sites such a basis for the choice ofconstruction would be un justifiably restricted andlead to unwarranted expense.

The acknow ledged procedure is to assess theseverity of exposure that is experienced at thelocation of the proposed building and then selectand specify a construction to provide theappropriate resistance to rainpenetration.

folloWing this methodical approach aconstruction thathas relatively low resistance torain penetration maybe quiteacceptable in asheltered locatio n, but be who lly inappropriatewhere more severe conditions areanticipated.

Location. site factorsandbuildingdesigncan increase the anticipatedseverity01exposure, but evenso, well consideredcavitywall construction can beeffective

ASSESSING EXPOSURE FOR SPECIFIC LOCATIONS

Assessmentofexposure to wind-driven rainshould be regarded as a necessary and worthwhilefirst step in the des ign proced ure. Whendetermining the likely expos ure of a building, themost exposed part shou ld be given particularattention andthis mayaffect decisions concerningthe choice of design and materials for the whole ofthe building.

Having determined the level of risk likelyto beexperienced the designer, using the guidance onresistance to rain penetrationof differe nt formsofconstruction and the factors affecting rain resistancedescribed in this Design Note, should select thematerials and form of construction that togetherwill provide adequate performance, paying dueregard to the importance of correct detailing andappropriate standards of workma nship .

In 1976 the Building Research EstablishmentReport Driving Rain Indez.' 1proposed a methodof assessing the quantity of rain falling on a verticalsurface such as a wall. Annualrainfall and average

windspeeds recorded at various meteorologicalstations throughout the United Kingdom could beused in calculationsto determine driving rainindices relative to the geogra phical locations ofproposed building sites. This method demonstra tedthe widevariation ofexposureto wind-driven rainexperienced nationally, but it was of limitedpractical value because of the rathergeneralisednature of the dataandthe assessment method.

Collection of data continued in the 1970'sand1980's and with the benefit of computeranalysts the Meteorological Office was able toproduce improved data, based on the observa tionthat prolonged rainfall was usually associated withstronger thanaverage winds.

A more refined and realistic method ofprediction was eventually developed and publishedby the British Standa rds Institution as BS8104Bri tish Standard Code ofpractice for Assessingexposure of walls to wind-driven rairP I. lt allowscalculationsof driving rainfall for different

Basedanexposure zonesdefined inBREReportBR262 Maximumwallspell indexcalculated usIng the/oca/ spell

Index methodspecifiedinBS 8104

orientations. It alsoallows annualaverage values tobe calculated as wellas quantities forthe worstlikely spellin any three year penod.

Rainfall varies considerably across the countrybut is largely unaffected by local features.Conversely, the general windspeed does not changemuchacross the country but It is affectedsignificantly by local features such as the spacingand height of neighbouling trees and buildings andwhether the ground is flat or rises steeply.

BS B104 permits corrections to be made forground terrain, topography,local shelter, and theform of the building concerned. These factorscanhavea majoreffect on the calculations and it isimportant to recognise that , because of theirinfluence,within any geographical localityconsiderable variation of exposure canbe expectedfrom site to site.

BS 8104 gives recommendations for twomethods of assessing exposure of walls in buildingsto wind-driven rain, namely the local spell indexmethod and the locol onnuol index method. Thelocol spell Index method should be used whenassessing the resistance of a wall to rainpenetration. The locol onnuol index is intended forusewhen considering the averagemoisture contentof exposedbuilding material or when assessingdurability, weathering and likely growth of mossesand lichens.

Categoryof Exposure

2

3

4

Sheltered

Moderate

5evere

Very severe

Colculatedquantity ofwinddriven rain {/it1f!$Im2 P'"~

Less than33

33 to less than 56.5

56.5 to less than 100

More than 100

Table 1 gives exposure categoriesdefined interms ofwoll spell indices calculated using the locolspell index method specified in BS 8104. Theindices, denved as they are frominherently variablemeteorological data, should not be regarded asprecise.Where assessment produces an index nearthe borderlinethe designer should decide which isthe most appropliate category forthe particularcase, using local knowledge and experience.

Table 1 is based on the 4 exposure zone seriesdefined in BRE Report BR 262 Thermal insulation:avoiding risksl31, which simplifies the 6 categoryseries specified in Table 10 of BS 5628 : Part 3British Standard Code of practice for the use ofmasonry : Materials and components, designand workmanship4J. As canbe seenin Table 1there are nooverlaps in the definition of the 4categories. Considerable overlaps in the definitionsof the 6 category series caused some confusion anduncertainty of interpretation. TheBR 262 series isthereforegenerally considered to be animprovement on the BS 5628 : Part 3 selies.

BR 262 provides a simple procedure forassessing exposure to wind-driven rain forwalls upto 12 m high. It is plimalily intended for low risedomestic buildings but may also be consideredsuitable forother categories of buildingsof similarscale.

The simplified guidance is based on a mapwhichdefines zones in which similar exposureconditions are predicted. Thepredictions are basedon calculations in accordance with BS 8104. Thezones arenumbered 1 to 4 and correspond withcategolies Shelteredto Very Severe as noted in Table 1.

The calculations defining the mapped zones inBR 262 assume "worst case" conditionsand soprovide very conservativeguidance. Using the BR262 map to predict exposure restlicts the choice ofconstructionbecauseit is not able to identify siteswithineach zone which may benefit fromshelterthat considerably reduces exposure to wind-drivenrain. Greater choiceof construction is justified bythe more specific assessment possibleby fcllowingthe B5 8104 method.

Tolile Classification ofexposure to localwind-driven rain

SELECTION OF MATERIALS AND CONSTRUCTION TO RESIST WIND-DRIVEN RAIN

The following factors affect the resista nce ofb rickwor k walls to winddriven rain. The order of thelisting does not indicate relative importance. Eachfactormust also be considered in relation to otherfunct ions of the wall such as st rength, dura bility,soundand thermal insulation: type of brick mortar composition thicknessof leaf presenceof a cavity width of airspace within any cavity mortar jointprofile and finish presence, type and thickness of any cavity

insulation architectural features and local practice presence of applied external surface finishes quality of workmanship to be achieved on site

Detailed considerations1 7'fpe of brick

Brick ty pes vary considerably in their physicalproperties, bu t when specifying brickwork withregard to resistance to wind-driven rain nodistinctionis made between them.

In a wall constructed of dense bricks, with lowwater absorption characteristics (for example thoseof the Engineering Classes) , on ly a relatively sm allquantity of water will be absorbed into the bricks.The greater proportion of any rainwate r falling on tothe wall will run down its face and may be blowninto a nd th rough it via paths in the mortar joints,particularly at the interfaces between the mortarand the bricks (see 6 below).

In contrast, in a wa ll of bricks havi ng relativelyhigh water absorption characteristics, such as manyhan dmade and stock bricks, much of the waterrunningoverthe wall surface in conditionsof

ABSORBENT

the "OVERCOAT" effect

DENSE

the "RAINCOAT" effect

driving rain will be ab sorbed into the bricks . If theduration of the rainfall is short this behaviour maybe conside red beneficial because it prevents mo st ofthe water reaching the mortar joints. However,when the surface of the material approachessaturation point water tendsto run more readilydown the surface and, as in wallsof dense units,may penetrate via paths at the mortar joints. Inverysevereand prolonged conditions ofdriving rainwater may be abs orbed further into t he bricks andeventually reach their inner surface, first asdampness andthen asfree water. Generally rainceases long before such complete saturation andwater is evaporated from the wall by the dryingeffect ofwindandairmovement.

These two modesof action are sometimesreferred to as the raincoat effect, inthe case ofdense, low absorption units, and the overcoat effect,in the case of high abso rption units . Solid wa llingcan ultim ately be pen etrated by prolongedexposureto wind-driven rain regardless of the waterabsorption characteristics of the bricks .

Although water abso rpti on va ries greatlybetween different bricks, this property has only arelatively small influe nce on the resistance of thefinished wall to wind-driven rain. In persistentconditions ofwind-driven rainwaterwill penetratemasonry leafs th rough the mort ar joints regardlessof the brick type.

Nodifference is detectable between the rainresistance of brickwork built of the va rious forms ofbrick unit, ie. so lid, frogged or perfo rated . Therehavebeen anxieties expressed that walls built ofperforated bricks m ight be less resist an t to winddrive n rain tha n those built with solid or froggedones, bu t such fears are unfou nded.

A reporton UK experience in the use ofpe rforated bricks, BRE Digest 273 Perforated claybricks'S), points out th at mo st of them are mad ewith bodies of low water abs orbe ncy an d th at , withregard to rain penetration, there is no evidence ofany significantdifference in performance betweensolid and perfo rated br icks with equivalent lowporosity bodies. It also comments that there is noevide nce to support the suggestion thatperforations may act as reservoirs in whichrainwa te r collects dunng rainy pe riods,subsequently giving rise to problems such asefflorescenceor frost attack.

2 M ortar compositionMortars vary in water permeability relative to

their cem ent content, high strength mortars ofDesignation ( i ) and ( ii It e.g. 1:0-1J.. a nd 1:'4 : 41/;ceme nt : lime: sand respectively, being the leastpermeabl e. These mortar Designations are oftenused in conjunctio n with dense, low waterabso rption fired clay bricks. This combination issatisfacto ry but should not be regarded as providinga waterproof. or near waterproof, co nstruc tion (see6 below).. Strong dense Designation ( i ) mortar is not

suitable for use with calc ium silicate bricks andse lection is governed by other facto rs such asaccom modati on of movem en t, durab ility andstre ngth. Designation ( iii ) an d ( iv I mortars areoften mo re appropriate for these bricks, eg 1:1:6and' :2:9 cement : lime: sand.

Foralternative mortar ty pes and mixes ofDesignations (i) to (iv) see Table 15 of BS 5628 : Part3. The ta ble lists various mixes for ceme nt, lime andsa nd mortars, masonry ceme nt and sa nd mortars,and mortars of ceme nt and sa nd with the additionof air-entra ining addi tives.

Of the various mixes specified for the mortars ofeach Designation those incorporating lime in th eircomposi tion show a n improvement in bonddevelopment and, as a consequ ence, a bett erresistance to rain penetration th an those morta rsbased on air entrainme nt a nd/or mineral materialsother than lime. Howeve r, although this advantageis detectable, it is not significa nt enough to justifylimiting the application of any particular type of mix.

3 Thickness of leafSolid wall construction of brickwork, in commo n

with ot her forms of ma sonry, gets wet whensubjected to ra in and absorbs so me of the wa ter,but when the rain sto ps it dries out again losing themoisture to the air by eva poration, an action whichis often accelerated by wind.

The resista nce to rain penetration of a solid wallis th erefore dependent upon its thickness a nd this isreflected in tradit ional const ructlcn - th in walls areused in very shelte red locations and th ick oneswhere exposure is greate r. Table 2 shows therecomm ended minimum thicknesses for bothrendered and unrendered solid wa lls for va riouscategories of expos ure.

Maximum recommended category ofexposure rsee "'bI' n

Thicknessof brickwork(mm)

90

2'5

328

440

Unrendered

(SlMJn I}

not recommended _"-51

not recommended 61

2

Rendered

{saMJrl: 2}

2

3

3

Extemallyinsulated(SarAAT3)

3

3

3

3

ImperviousCladding(SElNOff 4/

4

4

4

4

NaTE 1: A notional cavity should be providedbetween the internal surface of the masonry andany intem al lining.

NaTE2: Rendering should comply with BS5262.

NarE 3: External insulation should have a TechnicalApproval for use on solid walls subjected toExposure Category 3.

NaTE4: Examples of typical impervious claddingsyste ms are noted in 9 below.

NaTE5: Walls of half-brick thickness are Widely usedfor domestic garages and garden stores, but theymay be penetrated by persistent driving rain.

NarE 6: Historically 215 mm thick unrendered brickwallsare commonly found performing satisfactorilyin z-sto rev houses in towns and cities in the UK.Such locations are generally very sheltered wherelocal spel1 indices are of 20 11m2 or less .

nib e 2: Minimum thickness ofsolid brickworkwalls, with and without rendering. to resist rain penetrationin variouscategories 01 exposure (Based onTable 11 inBS 5628:Part31

Typicalsectionofcavity wall

'I.e Typical sectionofcavityw all at opening

>c--l'> __

~-~. ... ) .-_. -

. " -

For all practical purposes brickwork can beeffectively jointed with the mortars conventionallyused in traditional and modernconstruction, butthe jointsshould not be considered waterproof.

The brickto mortar interfaces in the wall are thepositions most vulnerable to rain penetration.Amicroscopiclabyrinth of voids exists at the interfacebecause of the physical nature of mortar bonding.The interface is also a likely location for capillarycracks dueto imperfect adhesionbetweena mortarand bricks. Good adhesion is difficult to achievewith absolute consistency and the interfacemay bedegraded further by crackingdue to moisture andthermal movements subsequent to construction.

The toolinginvolved in finishing joints such asthose with bucket handled and struckweatheredprofiles firms the mortar, reducing its permeabilityat the surface, and pushes it tight to the bricks,thereby improving its adhesion to them. Both

characteristics improve thejoints' resistanceto

penetration by water.Recessed joint

profiles form ledgeswhich impede therun-offof waterand

encourage it to enterthe walling at the

mortarI brick interfaces.Recessed joint profiles formed by rakingout themortarwithout subsequent tooling to firmitssurface further increases the vulnerability of thewall torain penetration. Recessed jointsalso reducethe width of the mortar joints. Compared withbucket handled and struck weathered profiles, therisk of rain penetration is greaterwith recessed

4 Cavity wallsTable 2 does not apply to cavity construction. In

cavitywallsit is accepted that some water willinevitablypenetrate the outer leaf in prolongedperiods ofwinddriven rain, but proper designandpositioning ofdampproofcourses and trays and ofany insulation willminimisethe riskof penetrationfurther into the building. Where the cavity isunavoidably bridged, e.g. at window and dooropenings, correct detailing is essential.

Cavity wallswith a half-brick thickouter leaf(90mm minimum)can performacceptably in allcategories ofexposure listedin table 1. Nevertheless,a designer mayconsider theuseofa thicker outerleafto reduce the quantityofwaterreaching the cavity.

No reliance should be placedon the inner leafofa cavitywall to resist waterpenetration.

6 Mortar joint, profile and finishRegardless of the type of brickor the mortar

composition, it is essential to fill completelyallbedjoints andcross joints (sometimes referred toas"perps" or "perpends") to minimise the riskof rainpenetration. Workmanship isvery importantin thisregard , see 10 below.

5 Width of air space within any cavityIn cavity walls the space between the two leaves

ofmasonry is intended to prevent any water frompassing from the outerleaf to the innerone. In mostsituations a cavitywallwith a half-brick thick outerleaf (90mm minimum), a SOmm cavity and an innerleaf issatisfactory. In conditions ofmore severeexposure considerationshould begiven to theuseof wider cavities.

Mortar joint profiles

joints and so they should only be used in Shelteredexposurecategory locationswhen resistance torainpenetration is important.

BucketHandle

StruckWeathered

Flush Recess ed

7 Cavity insulationThermal insulation materials may be effectively

installed within the cavity of a cavity wall toincrease itsoverall resistance to thermaltra nsmittance, thereby reducing heat loss from thebuilding. But if the insulation is not installedcorrectly, or without due care, its presencecanconstitute an increased risk of rain penetration ofthe wall tsee Thermal insulation: avoidingrisk9' 11.

Some insulation materials arebuilt-in so that afree airspace is retained,Le. a partial'fill system. Theretained air space shouldbe a minimum targetwidth of 50 mm. Inner leafconstruction of faceinsulated blocks require a retained air space.

In a fullfill system the cavity space between theinnerand outer masonry leaves is filled

wit h insulation material either bybuilding it in asconstruction proceedsor by injecting or blowing it into thecavity after the wall has been

completed . The cavity space should bea minimum target width of 50 mm, but

the riskof rainpenetrationwill be reduced if awider cavity isused,

Thermal insulation materials are provided in aform specifically intended for a particularinsta llation method. Products for partial fillapplications shou ld not be used for fullfill ones, an dvice versa. Only products specifically manufactu redforinsulating masonrycavitywallsshould be used;other forms of insulation material must neverbesubstituted. A summary of the types of materialsappropriate for use in partial-fill and full-fill cavitywall insulation systems is given in Table 3.

Some thermal insulation materials, egoinjectedfoamed urea forma ldehyde . are subject torestrictions of their use vis-a-vis severity ofexposure. All thermal insulation materials should bespecified and installed in acco rdance with therelevant British Standa rds, Technical Approvals andthe manufacturer's instructions.

The inclusion of insulation materials in a cavitywall sometimes requires the installation ofadd itional cavity trays (see page 19).

_Intem.rbrick or block

Cavity wall withpartial-fillcavity insulation

Cavity wall withfull-fillcavity insulation

mble3 Thennal insulation materials for use in cavityinsulated walls

Product..... ; ..

Partial-Fill Cavity Insulatian

Mineralfibreslabs

Foamedglass slabsExpanded polystyrenebead boardExtrudedexpanded polystyrene board ~Rigid polyurethane (PUR) boardPolyisocyanurare (P1R) board

Futl-Fill CavityInsulation

UTTS to U 811U.TIN

Mineralfibre bolts

LOOSEMAnxtAL TOU .. toWN IN

MineralfibrePolystyrene beadsPolystyrene granules

tNTCfU) FOAMD nASf1CUreaformaldehyde (UF) foam

Polyurethane (PUR} foam(/or stabilization and insulationofCavitywalls)

British Standard

3837 : Part 1 Specification

3837 : Port2 Specification4841 ' Part , Specification4841 : Part, Specification

6676 Part 1 Specification6676 Part 2 Installation

5617 Specification5618 Installation

7456 Instal/ation

7457 Sped{icotion

8 Architecturalfeaturesand lacalpracticeArchitectural featureshavean important affect

an the risk of rain penetraticn. Thedesigner shauldalwayscansider whether the destgn detailswillincrease the tendencyfor themasonry to be wettedmare than it wauIdbe by incident rainfall alone.

Examples of features thatcause concentratedwetting are:a) Anarea of glazing or imperviouscladdingcan

produce a large amountof surface waterrun -offandunless there is a gutter to collect it, oraprojecting sillto throw it clear, excessivewettingand possible waterpenetration canoccurin anymasanry below

b} Because of its profile a recessed bandcoursecancause local concentration of wetting.Corresponding intrusions intothe cavity duetothe setting back of bricksar ather masanry unitsto farm the feature may increase the riskof watercrossingthe cavity,Theuse of reducedwidthunitsto form the recesswould avoid intrusioninta the cavity Alternatively, the introductionofa cavity tray immediatelyabave the set-backmay be considered.Thedegreeaf welting of masanry canbe

reduced by ensuring that rainwater is thrown clearof the walls by adequate averhangs and drips ar byproviding drainage to takewater away from the masonry,

Append ix E of BS8104 contains a deta iledcommentary on the protection afforded byprojecting features such as sills, copings, stringcourses, roof eaves andverges. It explainswhysmall overhangsareso effective in protecting walls.

It might be anticipated that waterdripping from a projection wouldquickly be blown onto the wall a shortdistance below. However, airclose tothe wall forms an almost still boundarylayer and to the exte nt that it moves atall, it flows parallel to the surface.Because of this droplets falling fromprojections tend to fall vertically down tothe ground .

In general the Appendixcorroborates the beneficial effectstra ditionally asc ribed to projecting

features, but it also reports on studieswhichindicatethat in some conditionsof high winds anoverhang at the top of a wallcan lead to greaterwelli ng when compared with a flush topped wall.These findings are embodied in the allowancesrelating to gable ends and eaves to pitched and flatroofs in the BS 8104 method for assessing exposureto winddriven rain. The Appendix also reports onthe effect of surface texture and also theconcentration bywindof surface waterrun-offatexternal and internal corners of buildings.

The designer should always take account oflocal knowledge, experience and the evidence oflocal traditional forms of cons truction and buildingdetail. The fact that some building design featuresare not characteristic of a particular area orregionmay indicate their unsuitability for the rigours oflocal exposure.

Unsightly patchiness due to differences in wetness caused bythe application 01water repellent treatmentto brickwork at parapet level

9 Applied external surface finishesForboth smgle-leafand cavity walls, total

resistanceto rain penetration can be achieved onlyby the use of impervious cladding systems . lYpicallysuch systems are panels, boards or sheeting ofmetal, plastics or timber with weatherproof joints,andoverlapping slates, shingles. or tiles.

As indicated in Table 2 rendering cansubstantially enhance the rain resistance ofbrickworkwalls. It may be applied to solid walls andto cavity walls. It is essential, however, to select theright type of mortar mix , the thickness and numberof coats and to deta il the wall correctly in order tominimise shrinkage cracking, which mayotherwisereduce the effectiveness of the rendering. Therecommendations of BS 5262 British StandardCode ofpractice for external rendered finisheiJ6}and BCA publication Appearance matters - 2 :External rendering71should be followed .

The combination of full-fill insulation andrendering inhibitsthe drying out of any moisturethat may enter the outer leaf of masonry. Themoisture contentof the outerleafmayconsequentlyrise increasing the risks of frost action of themaso nry and sulfate attack of the jointing andrendering mortars. Claybricks of durabilitydesignations ML or MN las specified in BS 3921British Standard Specification for Clay brickiJ 8I1arenot recommended for such wallsin locationsexposed to Severe orVery Severe categories ofexposure to wind-driven rain. FL or FN claybricksmay be used.

In allcategories of exposurewhereFN orMNclay bricks are to be used behind rendering thejointingand render undercoat mortars should bemade with Sulfate Resisting Portland Cement ISRPCI.

The use of masonry paint systems (see BS 6150British Standard Code ofpractice for painting ofbuildingiJ911 and other proprietary external finishesincluding colourless treatments, e.g. silicone-basedwater repellents (see BS 6477 British StandardSpecification for water repellents for masonrysurfaceg.10Il, may increasethe resistance to rainpenetration. However. they may also reduce the rateof evaporation of any water from the wall and so themoisture contentof the wallcan increase ifwatergets behind the paint orsurface treatment eitherbypenetrating imperfections in it orentering fromadjoiningconstruction. In some cases this has leadto localisedwaterpenetration and/or saturationofthe brickworksufftcient to cause frost damage toclay bricks of ML and MN durability designation inwinter conditions.

Water repellent surface treatments arenotgenerally recommended for clay brickwork.Traditionally brickwork that is correctly specifiedand constructed is durable, withstands weatheringand resists the penetration of wind-driven rainwithout the needofwaterrepellent treatments.They should not be applied to clay brickworkwithout the approval of the manufacturer of thebricks specified.

10 Quality of workmanship to be achieved onsite

The qualityof workmanship actually achieved,both when constructing masonry andwheninstalling any insulation material, is the mostimportant factor affecting resistance to rainpenetration, All workmanship should be inaccordance with BS 8000 : Part 3 British Standardfor workmanship on building sites : Codeofpractice for masonry" l. Detailedguidance onworkmanship is also given in BOA Building Note 1Brickwork " Good site practice ' ' I.

Some brickwork requires particularcare initsconstruction compared with others. For example,considerclay bricks of low waterabsorption andthose of high water absorption. It has been statedthat allmortar joints should alwaysbe filled(see6above), but from the description of the raincoateffectand the overcoateffect (see 1above) it will beevident that minor imperfectionsin the jointing ofhigh water absorption bricks (overcoat effect) willnot alwaysbe critical. This is because. except in

"'Tipping andtailing" generally produces crossjoints with poorreslst ance te fain penetration

severe and Very Severecategories of exposure,mostperiods ofwind-driven rain are interrupted byadrying period beforethe bricks in the wall havebecome so saturated that the rain passes through .Bycontrastrain falling on a wallof low waterabsorption bricks(raincoat effect) will run downovertheirglass-like surfaces to enter immediatelyany imperfections in the jointing.

The importance of filling allmortar joints toensuregood resistance to rain penetration cannotbe overstated, but the cross-joints ("perps") are oftennot filled properly because they are formed using apoortechnique known as "tipping and tailing".Smalldabs of mortar are Wiped on the leading andtrailing edges of the end ofeachbrickwhen laying. This badpractice leads to cross-jointsthat are not adequately filledand therefore do not have thebest resistance to rainpenetration. Any anticipationthat the joints willsubsequently befilled by mortar flowing down into themfrom the next layer of bedding mortar is fallacious.Filling cross-joints by this means is impossible.Stretcherbonded walls have sixty cross-joints persquare metre and so if they are poorly filled theshortcoming can be significant. Filling cross-jointsproperly by applyinga fulllayer of mortar to theend ofeach brick is not difficult or time consuming.It is regarded as good practice and therefore it is notunreasonableto insist that it is done.

-Buttering- the endofa brickwithmortargives 8 fully filled cross joint

DAMP PROOF COURSES AND CAVITY TRAYS

Genera lAdamp-proof course(dpc) in a building is

intendedto provide a barrierto the passageofwater from the exterior of the building to theinterior, or from theground to thestructure, or fromone part of the structure to another.

Where the dpc is intendedto prevent theupward movement ofwater due to capillary actionthroughmasonrymaterials continuity is importantalthough, in normal circumstances, no hydrostaticpressureis involved. loints shouldbe made inaccordance with the instructions ofthemanufacturer of the dpc material used. Where nospecific instructions are given, the dpc shouldbelappeda minimum 100mm orthewidth ofthemasonry leafat comersorintersections. Penetrationofdpc's and cavitytrays by services, reinforcement,fixings, etc. shouldbe avoided as faras possible.Where they haveto pass throughcareshouldbetaken to form the necessary holeneatly andcarefully seal around the breach.

Where water is subjected to hydrostaticpressure, or ismoving ina downwards directionunder the Influence ofgravity, any jointsInthe dpcshouldbe madewaterproof by lapping and sealingfollowing the dpc manufacturer's specification forsealantor adhesive.

Opc's shouldextend throughthe full thicknessofa wall or leaf, and to the externalface whereitshouldbe clearly visible. Adpc shouldnot bebridged by pointing, rendering, plastering, walltiling, etc. To prevent penetrationofwater beneaththe dpc,whichcan occurIfit Isplaced directly on anirregular bed surface, and to producea goodbondto resistsubsequentmovement, dpc's shouldbelaid on a smoothbed offresh mortar. The use ofcoarseaggregates for the mortar shouldbe avoidedas they mightdamage the dpc. Sometimes dpc's areInstalled to form a slipplane to accommodatedifferential sliding movements betweenadjacentparts of the building structure; Insuch a case themortarbed shouldbe trowelled smooth, allowed toset, and then cleaned offbefore the dpc is laid.Alternatively, a doublelayerofappropriate sheetdpc materialwith no mortar or adhesive betweenthem may be specified.

itoove Ope's should be sandwiched betwee n mortar

PerformanceTo ensure adequate performance, dpc's and

cavitytraysshould havethe following materialproperties:(a) an expectedlife at least equal to that of the

building(b) resistance to compression without extrusion(c) resistance to sliding wherenecessary(d) adhesionto units and mortarwherenecessary(e) resistanceto accidental damageduring

Installation and subsequent building operations10 workability at temperaturesnormally

encountered duringbuildingoperations, withparticular regard to forming and sealing joints,fabricating junctions, steps and stop ends, andthe ability to retainshapetable 4 gives Information on performance of

Individual materialscurrently used fordpc's.BSB215 BritishStandardCode of practicefor

des/gn and installation of damp-proofcoursesin masonry construction " )gives guidance on thebasicprinciples concerning dpc's, their function andtheir Installation Inmasonry. Itcontainsrecommendations for the selection, designandInstallation ofdpc's Inboth solid and cavityconstruction.

Material

Rigid Materials

Resistant to extrusion :..... ~~~~'.~iii~l~ .ad

Ease ofiointing..:.

Limitationsor benefitsin use

OAr DI'C MICKS

complying with as3921SLAncomptying with as 743

Semi-Rigid MaterialsMASTIC AsnlALT Xcomplying with85 6925 or6577

..... .. . .. :... .

Flexible MaterialsUADSHET

comptyingwith as 1178COP1'EJt SHEET

compTying with C 104 orC 106ofBS2870

.t SUitable against rising moisture onlyGoodperformance in resisting flexural stress.

.t Suitableagainst riSing moisture only.

nf a

......; .

Requires protective coatingagainstcorrosion when setIn mortor > 25mm.Requires protective coatingto avoIdstaining masonry.

MTUMENSHEET

compTying withas 6398- withHessian base(class A)- withFibre base(class B). wtth Hessian base andlead (Class DJ. withFibre baseand lead(class E)

LOW DENSlTF 1'OLrETHnENI!SHEET

complying withas6515

rrTCH I"OLYMElI SHUT

~~~~

'"

Difficult to handleIn coldweatherDifftcultto handlein coldweather.Di/flcultto handleIncoldweatherDifftcultto handleIncoldweatherPoorbond performance. Norrecommendedtor use In conditions offlexural stress.Goodbondingperformance with mortar.

laDle 4 Summaryof materialsused for damp proof courses and cavity trays

Junct ionsDpc and cavity tray detailscan be simple and

straightforward in straight plainwalls, but atcorners, junctions, returns, curves, changes inlevel,changes in plane,around openings, etc., the needforcontinuity oftenrequires quite complicatedinstallation of dpc material. During the preparationofdetail design and specification for a buildingcareful consideration should be given to thesepositions and detailedthree-dtmenstonal drawingsmade ofalldpc's and trays at junctions, steps,angles and stop ends. Many common detailscannotbe formed satisfactorily In-situ, unless they arefabricated in lead. If materialsother than lead are tobe used in complex situations, then pre-formedcloaks shouldbe specified, so as to restrict the siteoperation to simple jointing.

Continuity and supportWhere practicable, dpc's and cavitytraysshould

be formed Ina continuouslength of material tominimise the need for joints.Cavity trays should besupportedat their joint positions to facilitateeffective sealing. Continuous support isadvantageous as it avoids sagging and deformation.

Resisting rising dampImmediately abovegroundlevel

In everyexternalwall, a dpc shouldbe providedat least 150 mm abovethe finished level of theexternal groundor paving. To preventthe transferofmoisture from external wallsintosolidfloors, thedamp'proofmembrane in the floor, and the dpc inthe wall, should overlap a minimum of 100 mm orbe sealed. In cavity workthe cavity should be filledto ground levelwith fine concrete, and weepholesshould be left In the vertical cross jointsof the outerleaf, at intervals not greater than 1 m, immediatelyabovethe top ofthis fill. The purpose of the fill is toprevent the leaves of the cavity wall beingdisplacedinto the cavity by pressurefrom the groundduringbackfill operationsorsubsequent loading ofthe ground.

BelowgroundlevelHorizontal and vertical dpc's are required where

the lowestfloor of the buildings is belowgroundlevel. Inthis situation it may be necessarytoconsidertanking (seeas 8102Bridsh StandardCode ofpracdce for protection of structuresagainst water from the groun d 14)).

---_ ... .....,."-'r'._-.--

Stop ends fmedtodiscontinuouscavity tray

Pre-formed cavity tray for anarch

Controlling downword movement ofwoterCavity walls

The design and specification of a cavity wallshould be based on the assumption that, inconditionsof persistent driving rain, water willpenetrate theouterleaf andrun down itsinnersurface within the cavity, Wherethe cavity isbridged, egoby lintels, structural beams, floor slabs,pipes, and ducts, dpc's in the form of cavity trays,with stop ends and weepholes, should be providedto divert water out again.

Over openingsIncavity walls, cavity trays should be provided

overall openings(including small openings forducts, services, etc), unless they arewell protectedby a roofor balcony overhang.

The cavity tray should step down or slopeacross the cavity not less than 150 mm towards theexternal leaf and, preferably, terminate in a smalldrip on the faceof the wall.

The cavity tray overan opening should overlapthe vertical dpc's at the jambs to ensure continuityof damp'proof measures (see figure on page' 8)

ArchesThe curved form of an arch makes the use of a

normal cavity tray impossible. A conventional cavitytray can be installed in the bed joint immediatelyabove the crown of an arch and for a minorsegmental arch in a relativelysheltered location thismay be considered acceptable. The tray shouldextend beyond the width of the arch and be filledwith stop ends. To improvethe construction shortlengths of flexible sheet dpc material can beset aroundthe curveof the arch in an overlapping arrangement.

A simpler and more reliable construction is touse a pre-formed arch tray (see figure above).Depending on the detail design of the opening thetray may be installed at the intradosor the extrados,i.e. under or over the arch ring.

Apre-formed tray should incorporate stop endsand, becausethearch form inevitablydrains anypenetratingwater toitsbearings, careshould be taken toensure effectiveweepholesareprovided.

WeepholesWeepholes are required in the outer leaf

immediately aboveany cavity tray so that watercollected on the traycan be diverted out to the exteriorof the building. They should be formed in verticalcross joints at intervals not greater than 1m. Thereshouldbe not lessthan two weepholes over eachopening.

It is usual to form weepholes by leaving anominal 10 mm wide cross jointunmortared.Theheightof the weephole is generallydetermined bythe height of the brickbut it is not critical. It shouldbe large enough to avoid any tendency to becomeblocked by debris. Weepholes formed betweensoldierbricks may be full height, but need only beabout 40 mm.

In tallbuildings subjected to harsh exposurethere has beenexperienceof rainpenetration duetohigh winds blowing into cavity wallsthroughweepholes and moving water up beyondtheupstand of dpc trays. Proprietarydevices areavailable to assist the formation ofweepholes thatallow water to drain from the cavitybut restrict theingressofwind andl or rain.

In this building there is a cavitytray inthefifth course above thesoldier course. Note theweepholesatthislevel- open crossjointsat900mm intervals

'Right Aproprietaryplastic windbaffleinsert toform aweephole

StopendsWheretrays arediscontinuous, andin a position

that is not wellprotected by a roofor balconyoverhang, stop ends should be filledat or near theends of the tray, generallycorresponding to cross

joints in the brickwork. Theyshould be bonded to the trayto givea waterproofseal.Stopends prevent the possibility ofwater in thecavity runningdown onto the tray and beingthrown offits ends into thecavity at the jamb ofan

openingsuch a concentrated flow ofwatercouldrun behind the verticaldpc in that part of thewalling, wet the inner leaf and lead to dampness ofthe internal faceof the wall. Stopends areparticularly desirablewhen cavityinsulation isinstalled.

Steel lintels are availablewhich are shaped andfinished to act as a cavity tray without the additionofsheet dpc material.These lintels also require stopends to be filled.

_ Tray ove, lintel -note stop ends

_ Vertical dpc wherecavity closed at jamb

Lapping of vertical dpcat jambs toopenings in cavrty wall

Arrangement ofvertical dpcand insulalion atjambs to openings in a cavity wall

Requirements for damp proof courses andcavity trays for specific parts of buildingsAt jambs of openings

Where a cavity wall is closed at the jambs ofopenings by masonry, a vertical dpc should beinserted to prevent moisture passing fromtheouterleaf to the inner parts of the wall. The vertical dpc

should extend into the cavity at least 25mm beyond the width of the closer andany cavity tray above should extendbeyond it tsee figure above). Insulationmaterial may also be placed in thisposition to minimize cold bridging.Proprietary closers are ava ilable whichcombine the functionsof closingthecavityat the jamb, preventingmoisture

transfer, stabilizing the masonry leaves, reducingcold bridging and providing fixingfor window ordoor frames. If these areused followmanufacturer'sinstructionsfor installation and linking withassoc iated dpc's at the head and sill.

A frame in an opening should be located andfixed in such a manner that transmissionof waterpast the vertical dpc is avoided . Where the frame isto be built in, the dpc should be secured to theframe first. If the frame is to be fixed later, the dpcshould be left projecting within the opening. Verticaldpc's at openings shou ld be positioned to overlapany horizontal dpc at the sill of the opening and beoverlapped by any cavity tray at the head [seefigure above).

A proprietary plastic cavitycloser I frame fixing

SillsAll pervious or jointed sills, or sub-sills, shou ld

be provided with a dpc for the full length and widthof the sill bed. The dpc should be overlapped by thevertical dpc's at the jambs of the openings [seefigure on page 18). Where the sill is in contact withthe inner leaf, the dpc should be turned up at theback and ends for the fulldepth of the sill(see figureon page 8).

Requirements for additional cavity trays withcavity insulation

When cavity insulation is present but notinstalled throughout the fullvertical height of thecavity (eg. stopped at eaves level in gable ends) acavity tray is required immediately above theinsulation to protect from the hazard of mortardroppings or other debris forming a bridging of thecavity on the top of the insulation .

In buildings over 12 m high, with insulatedcavity walls, cavity trays are required to subdividethe cavity so as to avoid surcharge by water thatmay penetrate the outer leaf of masonry. Theyshould be insta lled at a maximum of 12 m aboveground level and at a maximum spacing of 7 mthereafter. In framed building with brickworkcladding the trays required to subdivide the cavitycan be the same as those associated with thecladding support system .

In both these cases trays should step down aminimum of 150 mm towards the outer leaf andweepholes should be provided at intervals notgreater than 1 m.

Addrtional cavity tray 10protecttop of cavityinsulation

Additional cavity trays to subdividetall walls with cavity insulation

Detail of parapet showingdpc tray

External wall becomingan internal wallIf, in its height,an externalwallbecomes an

internal wall at lower level, as inthe case of a roofabutting a wall (e.g. ina stepped terraceofhouses,ora porch, garage orconservatory annex)a cavitytray shouldbe installed to drainthe cavity abovethe level of the lower roof.

Ahorizontal abutment requires a level cavitytray withstop ends and weepholes. When a pitchedroofabuts such a wall, a cavitytray stepped tocorrespond with the slopewill be required;alternatively a system ofoverlapping preformedtraysmay be installed to collect and dischargewater from the cavity. Ineithercase stop ends andweepholes are essential.

Proprietary systemsexist forthese applications.

ParapetsIna solid parapet wall a dpc shouldbe provided

at a heightofnot less than 150 mm above the topsurface of an abutting roofsystem and lap overtheflashing to the roofing to givecontinuity,

In a cavity parapet wall a cavity tray shouldbeinstalled to provide the same function. It shouldstep at least 150 mm within the cavity. When cavityfill insulation is installed the tray shouldstep downto the outer leaf(away from the roof]. When there isno cavityinsulation the designer should considercarefully which way to step the tray inany givencase. It is safer to directwater towards the outerface (away from the roof]. Concern that thismaycause staining on the face of the wall belowisexaggerated. Ifslopedinwards (towards the roof)experience showsthat there is a danger in thatrainwater may be driven below the tray and trackalong its underside and so gain accessto the innerleafof the wall, the underside ofthe roofcoveringand the interior of the building.

Itshouldbe noted that dpcs and cavitytraysimpairthe structural integrity of the parapet andthe wall beneath and also the coping above. Opcmaterialswithgoodbonding performanceshouldbe specified.

stability of the assembly the dpc can be placed in abeddi ng two or three courses below the topmostone . All materials above the dpc must be frostresistant. In cavity walls flexible dpc's requiresupport overthe cavity to avoid sagging anddeformation and to facilitate effective sealing oflapped joints.

Resistanceto waterpenetrationshould notprejudice provision formasonrymovement.Movement control joints in the masonryshouldbecarried th rough any coping or capping and sea lantapplied as in the corresponding joint in the wall below.

Consideration sho uld be given to copings andcap pings being displaced by lateral loads, and tothe possibility of vandalism. L-sha ped copings andclip-over copingsmay be more satisfactory insomesituations. Where necessary, copings should beSUitably fixed down and may be doweled or joggle-jointed together. Copings and cappings to thesloping tops of gable end walls present particularproblems of sta bility and security. They requirecareful consideration of the practicality of construction.

Brickwork withflush capp ings canbe very successful.butrequires extracare inthe selectionof materials for durabili ~tv. anundemanding oftheirweathering characteristics. andofthe implicationsofdesignfeatures onweathering

Copings and coppingsA coping is a construction that protects the top

of a wall and sheds rainwater clear of the verticalwall surfaces below, generally by having aweathered top surface and a throa ted overhang toone orbothedges. Acappingis a construction atthe top of a wall, but it does not shed rainwaterclear of the wall surfaces below. Cappings aregenerally flush, but they may have featu res which,althoug h they overhang the surface of the wallbelow, do not adequately protect it by throwingwater clear.The traditiona l detailof bricks set on-edge with tile creasing below sho uld be regarded asa cappi ng rather than a coping.

Preferably parapet walls, chimney terminals,freesta nding walls and retaining walls shou ld beprovided with copings. The drip edge of a throatingshould be POSitioned a minimum of 40mm from theface of the wall it is intended to protect. Where foraesthetic orotherreasons a cappingis used specialcare is needed in the choice of materials fordurability, both for the capping itself and for thewalling beneath.

Where the capping or coping is [ointed, acontinuous sheet dpc should be provided in thebedding mortarjoint.To increase the weight and

Copings givepositive protection againstwetting ofwallingbelow

ChimneysChimneys may be built in solid or cavity wall

construction. Wherea chimney stack isincorporated in an outer cavity wall, preferably theouterleafand cavityshouldbe continuous aroundthe chimney stack for the full height of the outerwalland then completely surround the chimneystac k whe re is projects above the roof. Corbellingfrom the chimney breast may be necessary belowthe roof line, to support the outer leaf at the sidesand back of the chimney stack.

If the chimneyis set inan internal partition orparty wall and the roof is steeply pitched, areasonable height of chimney willbe exposed in theroof void and any dampness in the masonry willbeable to dryout ina ventilated roofspace. However,with a low pitched roof, when a chimney is locatedat the eaves, or the roofspace accommodateshabitable rooms this beneficial effect will not applyand particular carein the design and constructionof the roof/chim ney intersection wtllbe necessaryto prevent moisture penetrating into the masonrybelow.

Opc trays should be provided to prevent thedownward passageof water. Horizontal traysshou ld extend through the thickness of the chimneywall and into the flue liner,with an upturn at theinner face of the flue. Externa lly it should be linkedwith any flashing at the intersection of the chimneywith the roof. The figure below illustrates typicalarrangements.

It should be noted that a sheet dpc at the pointof intersection with the roofreduces the structuralintegrity of the masonry, and the stability of thechimney stack and its resistance to lateral windloading needs to be considered. Chimney stacksbuilt in cavity work may be provided with a dpc trayof a materialstiffenough to form a cavity traywithout beingbuilt into the inner leaf and thisprovides structural continuity.

A horizonta l dpc should always be providedbelow any coping or capping at the top of the stackunless it is a jointless, waterresistant material, egoaone-piece dense terracotta, slate orreconstructedstone unit, or a sheet metal assembly in one-pieceor with waterproof joints.

StructuralframesMasonry supported by a structural frame,

requires particular attention to be paid to thedetai ling of trays and dpc's to ensure theircontinuity. Where cavity brickwork is supported onan edge beam, or floor slab, a cavity tray with aminimum upstand of 150 mm should be providedto prevent moisture penetration into the structure.The cavity trayshould be continuous around anycolumn, or other structural member, that obstructsthe cavity. When a structural memb er bridges thecavity, a vertical dpc should be included betweenthe structural member and the external leaf, andstop ends fitted to any ad jacent cavity trays.

Where complex shapes are needed,prefabricated cloaks should be considered tominimise difficulties of construction.

eft Opc trays andflashings in masonrychimneyat roof penetration

Flashings and weatheringsThe material to be used should be sufficiently

malleable to perm it dressing into shape, butsufficiently stiff to maintain its shapeand to resistlifting by the wind. Metal flashings other tha n leadshould, preferably, be pre' formed.

Flashings sho uld be bedded into the work aminimum of 25 mm, and be provided with welted ,orotherwise sealed, joints, oradequate overlaps.

Mostexternal wallsareexpectedto prevent rainpenetrating to the interior of buildings .

In masonrycavity walls it is acceptedthatsome water will pass thro ugh the outer leaf inprolonged periods of winddriven rain, but thedesign of the wall is intended to dea l with thisinevitable eventuality. The risk of furthe r penetrationthroug h the wall and into the building is minimizedby the proper des ign and installation of the wall'sassociated damp-proof systems.

Environmental and ecanomic benefits have ledto the incorporation of various types of thermal

1. Building Research Establishment. Repo rt DrivingRain Index (1976)

2. BS8104: 1992. British Standard Code of practicefor Assessing exposure ofwalls to wind-driven rain.

3. BREReport BR 262 : 1994. Thermal insulation:avoiding risks.

4. B55628: Part 3: 1985. British Standard Code ofpractice for the use of masonry: Materials andcomponents,designandworkmanship.

5. BRE Digest 273 : 1983. Perforated clay bricks

6. B55262: 1991. British Standard Code of practicefor external rendered finishes.

7 . British Cement Association publicationno.47.1 02. Appearance matters -2: Externalrendering (1992) W Monks

8. BS 392 1: 1985. British Standard Specification forClay bricks.

The designer shouldconsiderhow flashings aretobe fixed and at what stage in the constructionprogramme to provide secu re fixing and avoiddamage to dpc's. The materials should be selectedwith due regard to the likelihood of corrosion andgiven protective treatment asnecessary.

To avoidstaining of masonryfrom the run-off ofrainwater, consideration should begiven to theneed for surface treatment of somemetals.

CONCLUSION

insulationmaterials into modern cavity walls.Effectiveinstallation met hods have been deve lopedto ensure that this isdonewithout impairing thewall's performance in bad weather.

The incidence of wind and rain experienced inthe United Kingdom can be very testing, but wallswith facing brickwork can efficiently meet thecha llenge. With care and attention to design andworkmanship, stra ightforward and well establishedconstruction methods can provide wallsthat areresistant to rain penetration and also attractive,durable and economical.

REFERENCES

9. B5 6150: 1991. British Stan dard Code of practicefor painting of buildings .

10. B56477: 1992. British Standard Specification forwaterrepellents for masonrysurfaces.

11. B58000 : Part 3: 1989. British Standard forworkma nship on building sites : Code of practicefor masonry.

12. Brick Development Association Building Note 1. .Brickwork Good Site Practice. (1991)TLKnight

13. B58215: 1991. British Standard Code of practicefor design and installation of damp-proofcoursesinmasonryconstruction.

14. BS8102: 1990. British Standard Code of practicefor protection of structures against waterfromthe ground.

ISBNo 900191 OS 8

ACKNOWLEDGEMENTSAll photography by Brick Development Association except as follows:

Frankwalter - covers,p.u upper. p.21 lower

Cover & p.1IglI :z 1: Houses at Victoria Park. Virginia Water, Surrey....rchitects: The Howell Smith Partnership

Page 4: CascadesHotel and flats, Isle of Dogs, London E14Architects: ClWG

Page 11 upp er : Flats& maisonettes, Hadrian Estate,Hackney. London E2Architects: LevittBernstein Associates li d

Page 11 lower: CompassPomt HouSing. Isleof Dogs. LDndon E14Archuects: ~~mVD~on

Page 21 upper: HartlepooJeve Centre, develandArchitects: TheCulpm Partnership

Allenquir ies should be addressed to the autho r at the Brick Development Assoc iation.

The contents of this pubhcatmnare intended for generalguidance onlyand any person intendmgto use these contents for the purpose ofdesign. constructionorrepairof bnckworkor any related prcject should firstconsult a Professional Adviser.

TheBrick Development Association. Itsservants. and any persons who contributed to or who were In any way connected With this publicationaccept no babihtyarising fromnegligence or otherwisehowsoevercaused for any inluryor damage to any person or property as a result ofany use or reliance on any method,

product. instruction. idea,or other contents of this publication.