Can Passivhaus standards be met in the UK using

traditional cavity wall construction?

By

Michael Corran

Submitted in partial fulfilment

of the requirement for the degree

BSc(Hons) Construction Management

Leeds Metropolitan University

May 2012

i

Abstract

The UK Government has set an ambitious 80% reduction in greenhouse gas emissions

by 2050. The residential sector is responsible for 30% of the UK’s total carbon dioxide

emissions and is the focus for much of the Government’s efforts to reduce emissions.

The Code for Sustainable Homes, backed by the requirements of Part L1A, is the means

by which the UK Government is seeking to reduce emissions and energy consumption

in the domestic sector. An alternative, more ambitious, approach widely employed in

northern Europe is ‘Passivhaus’, which shows reduced energy demands of around 75%

compared to the German housing stock. The majority of these existing Passivhaus

certified dwellings use techniques (mostly timber frame, concrete and masonry with

external cladding), common to the country in which they are built, because of the

knowledge and skills present.

Masonry cavity wall construction comprises of 65% of the UK’s housing stock and is

the method most familiar to UK builders. This dissertation examines whether

Passivhaus standards can be met using traditional masonry cavity wall construction in

the UK. Denby Dale is the only current certified Passivhaus certified dwelling built

using cavity wall construction in the UK. The dissertation evaluates the way in which

the Denby Dale construction has been adapted to meet Passivhaus requirements and

using monitoring data collected by Leeds Met researchers, along with an interview with

the residents, assesses whether Passivhaus standards are met once the dwelling is

occupied.

Secondary research shows that the dwelling’s constructional aspects (walls, roof,

ground floor and windows) concerning heat transfer coefficients, thermal bridging and

airtightness are all within Passivhaus requirements and are acceptable. The mechanical

ventilation and heat recovery (MVHR) system efficiency is extremely high and easily

conforms to the Passivhaus standard. The primary research shows that the Passivhaus

requirements for primary energy demand, space heating demand, airtightness, thermal

comfort and indoor air quality have all been met.

The research shows not only that Passivhaus standards can be met using traditional

masonry cavity wall construction in the UK, but also that a 56% to 76% reduction in

emissions is possible compared to Part L 2010 UK Building Regulations. The

implications of these findings are discussed and a number of recommendations made.

The overall conclusion is that, although Passivhaus may be able technically to be

adapted to UK housebuilding techniques, there are still a number of constraints that

could affect its widespread uptake in the UK despite the undoubted benefits that it has

been shown to offer.

ii

Acknowledgements

I firstly owe my gratitude to John Bradley who has given me the opportunity to work on

this fascinating and current subject. John has not only been fantastic in this final year,

but also throughout my University experience. I am hugely appreciative of his

continued support and efforts. I cannot only say that John’s efforts and positive

approach have been acknowledged by me, but also by all students on the course. John is

a credit to the University and I wish him all the best for the future.

I would like to thank Leeds Metropolitan researchers, and in particular Ruth Sutton,

who have allowed me to use monitored data in relation to Denby Dale and have given

advice regarding this dissertation.

Much admiration goes to the Denby Dale residents who have taken a unique and

admirable step to transferring the Passivhaus concept to the UK. I would like to thank

them for their time and cooperation in relation to the interview, which has provided a

vital insight to the advantages Passivhaus has to offer. Furthermore I would like to

thank them for their consent, allowing me to use data related to their dwelling.

Finally I would like to thank my family who have provided endless support, allowing

me to be in the position of which I am now.

iii

Contents

Section Page

Abstract i

Acknowledgements ii

Contents page iii

List of Tables vi

List of Figures vii

Abbreviations ix

Chapter 1: Introduction 1

1.1 Problem Specification 1

1.2 Aim and Objectives 4

Chapter 2: Literature Review 5

2.1 What is Passivhaus? 5

2.2 Construction fundamentals 8

2.2.1 Good thermal insulation and compactness 9

2.2.2 Thermal bridging 9

2.2.3 Windows and doors 10

2.2.4 Airtightness 11

2.2.5 Mechanical ventilation and heat recovery (MVHR) 11

2.3 Passivhaus Planning Package software (PHPP) 12

2.4 Most common Passivhaus construction methods 12

2.5 UK housing construction methods 15

2.6 Conclusion 17

.

Chapter 3: Methodology 19

3.1 Introduction 19

3.2 Secondary research 19

3.3 Primary research 20

iv

Chapter 4: Research findings 1: Denby Dale construction methods

and detailing 22

4.1 Introduction 22

4.2 Foundations and ground floor 23

4.2.1 Passivhaus U-value requirement comparison 24

4.2.2 Airtightness detailing 25

4.3 Wall structure 27

4.3.1 Passivhaus U-value requirement comparison 29

4.3.2 Airtightness detailing 30

4.4 Roof structure 30

4.4.1 Passivhaus U-value requirement comparison 30

4.4.2 Airtightness detailing 30

4.5 Windows and doors 33

4.5.1 Passivhaus U-value requirement comparison 34

4.5.2 Airtightness detailing 36

4.5.3 Thermal bridging, THERM analysis 36

4.6 First floor construction and airtightness detailing 40

4.7 Airtightness testing 41

4.8 Mechanical ventilation and heat recovery system (MVHR) 42

4.9 Summary 43

Chapter 5: Research findings 2: Denby Dale performance 45

5.1 Introduction 45

5.2 Primary energy demand 46

5.2.1 Comparison to Passivhaus requirement 49

5.3 Carbon dioxide (CO2) emissions 49

5.3.1 Comparison of SAP and PHPP factors 52

5.4 Space heating demand 53

5.4.1 Comparison to Passivhaus requirement 58

5.5 Distribution of energy use 58

5.6 Indoor carbon dioxide (CO2) levels 60

5.7 Internal temperature 65

5.8 Internal relative humidity 68

v

5.9 Subjective assessment of maintenance, operations and comfort by

occupants 73

5.10 Summary 76

Chapter 6: Conclusions 78

6.1 Implications and Recommendations 81

Bibliography 84

Appendices 94

vi

List of Tables

Table …. … Page

1: Criteria for Passivhaus certification 6

2: Fresh air heating limitations 7

3: Passivhaus specification summary 8

4: Passivhaus requirements relating to construction fundamentals and MVHR

system 22

5: Denby Dale ground floor U-value calculations and Passivhaus U-value

insulation requirements 25

6: Denby Dale wall U-value calculations, with Passivhaus U-value insulation

requirements 29

7: Denby Dale roof U-value calculations, with Passivhaus U-value insulation

requirements 31

8: Denby Dale window specifications in relation to Passivhaus requirements 34

9: First Denby Dale blower door test results 42

10: Denby Dale annual energy usage, with Passivhaus requirement in relation to

primary energy demand 48

11: Denby Dale primary energy demand calculation 49

12: Primary energy usage and PHPP CO2 emission factors 51

13: Primary energy usage and SAP CO2 emission factors 51

14: Gas energy usage and solar thermal readings, required for annual DHW

estimation 54

15: Gas energy usage, solar thermal readings and boiler switched off, required for

annual gas cooking estimation 56

16: Denby Dale range and average CO2 levels (ppm) from 20/07/2010 to

06/01/2012 62

17: Highest average CO2 concentrations measured within Denby Dale 63

18: Lowest average CO2 concentrations measured within Denby Dale 64

19: Comparison of Passivhaus standards and Denby Dale’s performance 77

vii

List of Figures

Figure Page

1: Linear thermal conductivity Ψ ≤ 0.01 W/mK 9

2: Triple glazing window with an overall U-value of 0.8 W/m²K 9

3: Passivhaus construction methods in Austria 13

4: Passivhaus construction methods in Germany 13

5: Masonry wall with external cladding 14

6: Passivhaus wall detail timber construction 15

7: UK housing construction type by dwelling ages 16

8: Traditional cavity wall structure 17

9: Denby Dale foundations and ground floor, cross section 24

10: Service penetration at ground floor 26

11: Denby Dale cavity wall and cavity tray 27

12: Denby Dale cavity wall 28

13: Denby Dale roof and wall junction, cross section 33

14: Ecopassiv window 34

15: Denby Dale window detailing 35

16: Denby Dale window detailing, cross section 36

17: Denby Dale window junction, isotherms produced in THERM 37

18: Denby Dale window junction, colour infrared produced in THERM 38

19: Denby Dale window junction, colour flux magnitude produced in THERM 39

20: Denby Dale window junction, flux vectors produced in THERM 39

21: Denby Dale first floor junction, cross section 41

22: Blower door airtightness test 41

23: Denby Dale MVHR system 43

24: Denby Dale south elevation 46

viii

25: Comparison of carbon dioxide equivalent emissions produced from primary

energy usage 52

26: Denby Dale average daily energy consumption and generation 55

27: Denby Dale average daily energy consumption and generation 57

28: Specific energy consumption 58

29: Comparison of primary energy consumption: Denby Dale and UK homes 59

30: Denby Dale daily average CO2 concentrations 61

31: Denby Dale ventilation ducting 66

32: Denby Dale daily average temperatures external and internal 67

33: Denby Dale daily average RH for internal and external environments 69

34: Denby Dale external temperatures and internal humidity comparison 71

35: Relationship between lounge RH and external temperature 72

36: Denby Dale south elevation 95

37: Denby Dale south-east elevation 95

38: Denby Dale north elevation 96

39: Denby Dale Vaillant gas boiler and STHW storage tank 96

40: Denby Dale MVHR system in garage 97

41: Denby Dale supply and extract ducts 97

42: Denby Dale ground floor, plan 102

43: Denby Dale first floor, plan 103

44: Denby Dale north elevation 104

45: Denby Dale east elevation 105

46: Denby Dale south elevation 106

47: Denby Dale west elevation 107

ix

Abbreviations

ach Air changes per hour

AECB Association of Environment Conscious Buildings

BRE Building Research Establishment

CCC Committee on Climate Change

CO2e Carbon dioxide equivalent

CEPHEUS Cost Efficient Passive Houses as a European Standard

DCLG Department for Communities and Local Government

DECC Department of Energy and Climate Change

GBM Green Building Magazine

GBS Green Building Store

GDP Gross Domestic Product

GHG Greenhouse gases

HTC Heat transfer coefficient

HSE Health and Safety Executive

IBO Austrian Institute for Healthy and Ecological Building

IPCC Intergovernmental Panel on Climate Change

iPHA International Passive House Association

K Unit of measurement for temperature Kelvin

kWh Kilowatt hours

kWh/(m²/a) Kilowatt hours per square metre per annum

Kyoto GHGs Carbon dioxide, methane, nitrous oxide, sulphur hexafluoride,

hydrofluorocarbons and perfluorocarbons

MtCO2e Million tonnes of carbon dioxide equivalent

MVHR Mechanical ventilation and heat recovery

m²K/W (R-value) Square metre per Kelvin per watt

x

m³/pers/h Cubic metre per person per hour

NAU Northern Arizona University

NBT Natural building technologies

NHBC National House Building Council

N/mm² Newton per square millimetre

Pa Pascal

PE Primary energy

PEP Promotion of Passivhaus

PHI Passivhaus Institute

PHPP Passivhaus Planning Package

ppm Parts per million

RH Relative humidity

SPED Specific primary energy demand

U-value Heat transfer coefficient

Uf Frame U-value

Ug Glazing U-value

W/mK Watts per metre Kelvin

W/m² Watts per square metre

W/(m²K) Watt per square metre per Kelvin

W/person Watts per person

Ψ Psi, linear thermal transmittance

Ψg Psi, linear thermal transmittance of glazing to frame junction

1

Chapter 1: Introduction

1.1 Problem Specification

According to the Department of Energy and Climate Change (DECC, 2011a) the UK

emitted 566.3 MtCO2e of greenhouse gases (GHG) in 2009, representing only 2% of

global carbon emissions (IEA, 2011) yet, despite this, the UK has set some of the most

ambitious carbon emission reduction targets. The Climate Change Act 2008 sets out

legally binding targets committing the UK to reduce GHG emissions, and states ‘It is

the duty of the Secretary of State to ensure that the net UK carbon account for the year

2050 is at least 80% lower than the 1990 baseline.’ (Climate Change Act 2008, c.27).

The Stern Review (Stern, et al., 2006; Tol, 2006) was a major factor in persuading the

UK Government to adopt such a demanding target, Stern argued that stabilising GHG

concentrations between 450ppm and 550ppm CO2e would be manageable and at a

reasonable cost: ‘expected annual cost of emissions reductions consistent with a

trajectory leading to stabilisation at 500ppm CO2e is likely to be around 1% of GDP by

2050’ (Stern, et al., 2006, pp. xii). The research predicted, in economic terms, the

consequences of not adhering to this upper bound 550ppm CO2e target could lead to an

average reduction of 10% global GDP.

Stern et al. (2006) believe that atmospheric levels above 550ppm CO2e would most

likely see an increase to the global average temperature of 2˚C. To prevent this,

significant reductions in global GHG emissions must be made. Agreements on a set of

mutual responsibilities, considering costs and the ability to bear with them, will

contribute to the overall goal of reducing the risks of climate change. Richer countries

based on income, historic responsibility and per capita are expected to take

responsibilities for emission reductions of 60-80% by 2050 (ibid).

2

A report published by the Committee on Climate Change (CCC, 2008) states that an

80% reduction of GHG emissions by 2050 would be an appropriate measure to enable

the UK to contribute towards reducing global Kyoto GHG emissions by 50-60%. The

Climate Change Act introduced ‘carbon budgets’ which set the trajectory limits on total

GHG emissions over 5 year periods, and are also legally binding (DECC, 2012b). The

CCC (2008; 2010) recommends GHG reductions of at least 34% by 2020 against 1990

baseline levels, with further reductions to 42% if and when there is progress towards

agreements to reduce global emissions. The fourth carbon budget, 2023-27, requires

emission reductions of 50%, and a total of 60% by 2030, relative to a 1990 baseline

(DECC, 2011a). The CCC (2010) states that a further 60% reduction in GHGs will be

required between 2030 and 2050 to meet the 2050 target.

The UK residential sector released approximately 149 MtCO2 in 2010, accounting for

30% of the UK’s total CO2 emissions (DECC, 2012a).The sector has consequently been

on the Government’s agenda to drastically reduce its GHG emissions. The Government

is pressing to make an impact on energy usage and emissions within the UK domestic

sector by introducing strict regulations to be applied to new dwellings. However if the

UK housing stock is to reduce CO2 emissions in line with the Climate Change Act then

energy consumption in new builds must be dramatically reduced.

The Code for Sustainable Homes is one action taken by the Government to improve the

energy efficiency of UK homes and reduce related CO2 emissions. Building Regulations

Part L1A requires a 25% decrease in CO2 emissions from Part L 2006 which meets the

requirements of the Code for Sustainable Homes level 4. Levels 5 and 6 are geared to

meet 100% and true zero carbon reductions to meet future targets (DCLG, 2009).

Alternatively the German approach to sustainable building ‘Passivhaus’ has undergone

extensive research (CEPHEUS, 2001; Williamson, 2007) which has shown that

3

Passivhaus dwellings in Germany are 75% more efficient and can save approximately

5.6 tonnes of GHG emissions per dwelling. The previous Secretary of State for Energy

and Climate Change, Chris Huhne, acknowledged the need for more efficient housing

and has argued that all new homes in the UK should meet the Passivhaus standard

(Kennet, 2010). Jonathan Porritt, the founding director of Forum for the Future, has also

backed Huhne’s view and has called on the UK construction industry to embrace the

Passivhaus Standard to aid in meeting the Government’s 2016 zero-carbon housing

target. Porritt has stated: ‘We’re going to have to be doing a huge amount to catch up.

We’re going to have to see an unprecedented wave of innovation around construction

techniques and design. For me it’s really important that what’s been going on elsewhere

particularly in Germany with Passivhaus is now brought in as part of that innovation

cycle in the UK,’ (Kennet, 2010, p.1).

Despite the overwhelming evidence of the Passivhaus standard in achieving low energy

demands, the UK has been slow to adopt the concept. The UKPH conference (2011)

state that as of October 2011 the UK only had 70 projects either certified or in progress,

whereas there are in excess of 30,000 Passivhaus dwellings constructed worldwide

(BRE, 2011). This is because the Passivhaus dwellings have been constructed using

construction techniques common to the region (Williamson, 2007). The UK

construction industry, however, traditionally uses cavity wall construction (DCLG,

2008) a technique of which is not widely used for dwellings built to Passivhaus

standards. Brunsgaard, Heiselberg and Jenson (2008) state that one of the main barriers

is the current inability to build Passivhaus dwellings using traditional construction

techniques such as cavity wall construction.

The UK would benefit profoundly from the proven reductions in CO2 emissions and

increased energy efficiency provided by the Passivhaus standard. However successfully

4

adapting the Passivhaus standard using techniques common within the UK (cavity wall)

is the major barrier preventing the transition.

There is currently only one Passivhaus certified dwelling in the UK built using cavity

wall construction. The dwelling has been constructed by the Green Building Store

(GBS), and is situated within Denby Dale, West Yorkshire (GBS, 2010a). However

analysis of the dwellings performance, as that undertaken by CEPHEUS, has not been

conducted as of yet. It is important to define the constructional aspects used by GBS

which allowed for Passivhaus certification. Furthermore determining whether the actual

performance of the dwelling once inhabited meets Passivhaus certification.

1.2 Aim and Objectives

Therefore the aim of this dissertation is to evaluate whether Passivhaus standards are

applicable in the UK using cavity wall construction. It does so by:

Analysing the principles of the Passivhaus standard

Ascertaining the most appropriate methods used to obtain primary and secondary

research concerning Denby Dale

Assessing whether cavity wall construction detailing used at Denby Dale enables the

dwelling to achieve the Passivhaus standard, and how this has been accomplished.

Investigating whether the Denby Dale dwelling performs to the Passivhaus standard

once constructed.

Drawing conclusions from the analysis to assess whether the Passivhaus standard

can be met in the UK using cavity wall construction and the implications for

applying this concept in the UK.

5

Chapter 2: Literature Review

2.1 What is Passivhaus?

PHI (2011b, p.1) states that ‘The term Passivhaus is used for an internationally

established building standard with very low energy consumptions, which have been

proven in practice’. The Passivhaus concept was initially developed in 1988 by

Professor Bo Adamson and Dr Wolfgang Feist. The first Passivhaus was built in 1990

and the Passivhaus institute formed in 1996 (NBT, 2009).

The number of Passivhaus certified dwellings has grown rapidly in the past few years.

NBT (2009) acknowledges that there were approximately 15,000 buildings which

comply with Passivhaus standards in 2009. This rose to over 20,000 by early 2010

(iPHA, 2010), and now currently exceeds 30,000 buildings worldwide, around 20,000

of which are in Europe (Passivhaus Trust, 2011; BRE, 2011).

Passivhaus requirements can aid in the approach of reaching zero carbon buildings.

Although the Passivhaus standard is not in itself carbon neutral, the requirements

dramatically reduce the energy requirements which can be more readily met by

renewable technologies (Hodgson, 2008).

IBO (2008, p.14) defines a Passivhaus as ‘a building in which thermal comfort is solely

guaranteed by re-heating (or re-cooling) the volume of fresh air that is required for

satisfactory air quality - without using circulation air’. This is a purely functional

definition. Passivhaus also refers to the way in which thermal comfort is guaranteed by

passive measures where possible; such as thermal insulation, heat recovery, passive use

of solar energy and interior heat sources (IBO, 2008).

6

Dwellings can only be awarded the ‘quality certified Passivhaus’ certificate, by the

Passivhaus Institute. The requirements for Passivhaus certification are set out in a

number of performance standard, shown in Table 1.

Table 1. Criteria for Passivhaus certification (Source: IBO, 2008; PHI, 2010)

Value Calculation method

Space heating demand ≤ 15 kWh(m²/a) PHPP

Heating load ≤ 10 W/m² PHPP

Airtightness 0.6 ach @ 50 Pa*

Blower door test, n₅₀ value

measured according to EN

13829

Primary energy demand ≤ 120 kWh(m²/a) PHPP

*0.6 ach @ 50 Pa - air changes per hour at 50 pascals of pressure, measured using a

blower door test.

PHI (2010) states that the frequency of temperatures higher than 25˚C (summer

overheating) should be no greater than 10%. Passivhaus conditions can also be

quantified. Table 2 shows the ventilation requirements per person and the maximum

temperature fresh air can be heated to without dust pyrolysis.

Table 2. Fresh air heating limitations (Source: IBO, 2008)

Minimum fresh air

volume for one

person

Air heat capacity at

21˚C and normal

pressure

30K warmer

than room air Equal to

30 m³/pers/h 0.33 Wh/(m²K) 30 K 300 W/person

IBO (2008) explains that the fresh incoming air can be heated to a maximum of 50˚C,

because higher temperatures will lead to dust pyrolysis and burning smells. This

explains the additional 30K heating to approximate room temperature air at 20˚C.

Experience and calculations made with simulation programs, such as PHPP, has shown

7

that a maximum heating requirement of 15 kWh/(m²a) is common for Central Europe

(IBO, 2008). Hodgson (2008) explains that the space heating demand is limited to 15

kWh/(m²a) because a comfortable 20˚C indoor temperature needs to be achieved in

areas of low ventilation rates. This means that only a certain amount of heat can be

supplied without exceeding the 50˚C temperature limit.

Passivhaus is not just concerned with energy efficiency. Equally important, and related,

is the achievement of thermal comfort. The PHI (2011b, p.1) states that:

A Passive House is a building, for which thermal comfort (ISO 7730) can be

achieved solely by post heating or post cooling of the fresh air mass, which is

required to fulfil sufficient indoor air quality conditions (DIN 1946) - without a

need for re-circulated air.

Thermal comfort as defined in British Standard BS EN ISO 7730 is ‘the condition of

mind which expresses satisfaction with the thermal environment’. The perception of

‘thermal comfort’ usually refers to a person feeling too hot or too cold (HSE, 2011a),

varies from person to person. Passivhaus dwellings are required to satisfy the majority

of people, which is expressed as ‘reasonable comfort’ and considers 80% of the

population (ibid).

The HSE (2011b) explains that there are four environmental factors (air temperature,

radiant temperature, air velocity, humidity) and two personal factors (clothing

insulation, metabolic heat) which determine thermal comfort. Passivhaus standards are

related solely to environmental factors. Heat demand calculations used to specify

Passivhaus standards are based on achieving a room temperature of approximately 21˚C

(IBO, 2008), which research (Isaksson, 2005 cited in Environmental Change Institute,

2007) shows is considered to be acceptable when concerning thermal comfort.

Thermal comfort must be achieved by heating and cooling of fresh air i.e. by the use of

MVHR systems. Isover (2007) expands on the term ‘thermal comfort’ in Passivhaus

8

dwellings and states that the enclosing walls, floors and windows should have a similar

temperature to the surrounding air.

According to IBO (2008) Passivhaus dwellings should achieve humidity levels of

approximately 50%. HSE (2011b) states that 40% to 70% humidity does not affect

thermal comfort. Humidity levels of more than 60% can cause growth of mould and

mildew (NAU, 2009).

2.2 Construction fundamentals

To obtain Passivhaus certification, a building must have been modelled using the

Passivhaus Planning Package (PHPP) and meet the criteria in Table 3. These are

explained in more detail in Chapter 4.

Table 3. Passivhaus specification summary (Source: IBO, 2008; PHI, 2011b)

Measure Passivhaus standard

Ground floor U – value ≤ 0.15 W/m²K

Walls U – value ≤ 0.15 W/m²K

Roof U – value ≤ 0.15 W/m²K

Window and doors U – value ≤ 0.8 W/m²K

Window glazing U – value ≤ 0.6 W/m²K

Thermal bridging Ψ ≤ 0.01 W/mK*

Airtightness 0.6 ach @ 50 Pa**

Ventilation MVHR

efficiency ≥ 75%

Max heat load ≤ 10 W/m²

Max space heating ≤ 15 kWh/(m²/a)

Max annual PE ≤ 120 kWh/(m²/a)

* Ψ - linear thermal transmittance, refers to the additional heat loss (or gain) through the

building envelope per meter length of that detail.

9

2.2.1 Good thermal insulation and compactness – [U- value ≤ 0.15 W/m²K]

The building shell requires a continuous envelope of outstanding thermal insulation.

IBO (2008) claim that Passivhaus dwellings in central Europe achieve heat transfer

coefficients (U-value) of between 0.1 and 0.15 W/m²K, and any construction method

has the ability to achieve this. The high levels of insulation enable a Passivhaus

dwelling to reach high levels of thermal comfort with little heating demand. The high

levels of insulation also provide protection during the summer when temperatures are

higher. IBO (2008, p.17) explains: ‘Highly insulated structures have high temperature

amplitude absorption, even with low mass. Thus daily outside air temperature

fluctuations have no noticeable effect within the building.’ This increases residential

comfort as cooling a Passivhaus dwelling is easily achieved by window ventilation.

IBO (2008) explains that Passivhaus standards are more easily achievable with compact

designs, where the ratio between the outer surface and the heated volume of the

dwelling is as low as possible. Heat loss is reduced with a small external surface.

2.2.2 Thermal Bridging - [Ψ ≤ 0.01 W/mK]

A thermal bridge-free construction is a basic requirement of the Passivhaus standard

(PEP, 2006). Attention must be paid to the detailing and execution around connections

with windows, door frames, floors and roofs. The linear thermal conductivity of these

elements should be lower than 0.01 W/mK for connections in the thermal envelope in

reference to external dimensions (PEP, 2006). Figure 1, shows the modelling of a

timber frame construction, with a linear thermal conductivity of 0.055 W/(mK). PEP

(2006) claim that typical values for linear thermal conductivity within Passivhaus

dwellings range from 0.03 to 0.01 W/mK. These thermal bridges are required to be

minimised in all details and not just windows and doors.

10

Figure 1. Linear thermal conductivity Ψ ≤ 0.01 W/mK

(Source: SINTEF Byggforsk, PHI, ProKlima cited in PEP, 2006).

2.2.3 Windows and doors - [U- value ≤ 0.8 W/m²K]

Windows and doors must be triple glazed and the glazing alone must achieve a U-value

below 0.6 W/m²K. The overall window/ door, including the frame and glazing

combined must achieve a U –value below 0.8 W/m²K to meet Passivhaus requirements

(IBO, 2009). Windows which have the ability to achieve such an outstanding U-value

are the best available. IBO (2008) explains the three main design features incorporated

within these windows are: three-pane thermopane glazing or a comparable glass

combination, “warm edge” spacers and specially insulated window frames. Figure 2

shows a triple glazed window which includes these features (IB0, 2008).

Figure 2. Triple glazing window with an overall U-value of 0.8 W/m²K (Source:

PassivHaus Institut PHI, Passiefhuis-Platform vzw, cited in, PEP, 2006)

Ψ = - 0.055 W/(mK)

11

2.2.4 Airtightness - [0.6 ach @ 50 Pa]

Passivhaus dwellings require high levels of airtightness to reduce space heating

requirements, which also aids in preventing draughts and accumulation of moisture

which would affect buildings’ performance and lifespan. High levels of airtightness

reduce natural ventilation in Passivhaus dwellings, and therefore require some form of

ventilation system. The Passivhaus airtightness requirement is a maximum of 0.6 air

changes per hour at 50 pascals of pressure (0.6 ach @ 50 Pa) (PHI, 2011b).

PHI (2011b, p.1) states that the key principle Passivhaus dwellings use, concerning

airtightness is ‘continuous uninterrupted airtight building envelope’. Achieving this

requires use of tapes, membranes, wet plaster, and vapour membranes, to create a

continuous airtight barrier. Particular attention is required at different element

connections such as doors and windows (Hodgson, 2008; PEP, 2006).

The airtightness of a dwelling is measured using a blower door test (fan pressurisation),

usually undertaken during construction to allow any weaknesses to be rectified (Leeds

Met, 2010)

2.2.5 Mechanical ventilation with heat recovery (MVHR)

Window ventilation would be insufficient, ineffective and prevent Passivhaus

dwellings’ heating requirements from being achieved. The health and comfort of

occupants is the most important feature within Passivhaus planning and therefore a

mechanical ventilation system is required at least (Hodgson, 2008; IBO, 2008).

To meet the extremely low energy Passivhaus space heating requirements

(15kWh/(m²/a)), a heat recovery system must be incorporated within the ventilation

system, with efficiency in excess of 75% and low specific fan power (ibid). Therefore a

12

Mechanical Ventilation with Heat Recovery (MVHR) system is required to replace and

maintain the air quality at a rate of 30 m³/person/hour to ensure reasonable air quality

according to PHI (2011b). The system removes unwanted odours, moisture and carbon

dioxide, whilst providing fresh air. The heat exchanger does not mix exhaust air with

fresh air but simply exchanges the heat from exhaust air to incoming fresh air

(Hodgson, 2008).

Heat recovery efficiencies range from 75 to 95% for Passivhaus standards, with aspects

such as duct work insulation, used to optimise system performance (PEP, 2006). Any

units which have not been certified by the PHI receive an efficiency penalty of 12% on

the manufacturer’s claims, therefore making it much more difficult to achieve specific

space heating requirements of 15 kWh/(m²/a) (IBO, 2009).

2.3 Passivhaus Planning Package software (PHPP)

PHPP is an excel based software package created to assist in the design of buildings

which aim to achieve the Passivhaus standard (AECB, 2006) The PHPP has been

proved reliable, as simulation data has been compared with actual measurement data

and shown to have close correlations (AkkP5, cited in: PHI, 2011a).

According to the PHI (2011a) the PHPP requires over 2000 independent input data. The

data must be in accordance with the geometry of the building in order to obtain accurate

results. The PHPP software treats the building and mechanical equipment as one overall

system (ibid).

2.4 Most common Passivhaus construction methods

The majority of Passivhaus dwellings in Northern Germany comprise of masonry walls

with external insulation, whereas 80% of Passivhaus dwellings in Southern Germany

and Austria are timber frame construction (Williamson, 2007). The percentages for

13

construction methods for Passivhaus in Germany and Austria can be seen in Figures 3

and 4.

Williamson (2007) believes that different construction systems are used to build

Passivhaus dwellings due to traditional construction practices and vernacular

architecture varying regionally. All three systems (timber frame, concrete, and masonry

with external cladding) have been proven to achieve the Passivhaus standard. The most

widely used construction methods masonry and timber frame, are briefly discussed

below.

External cladding/masonry

Masonry constructions provide good thermal mass. Thermal mass absorbs heat from the

direct sunlight and heat ventilating around the thermal wall (Chiras, 2002). Thermal

mass is particularly effective within Passivhaus concrete floor structures. The thicker

the slab the more heat stored and the longer it will release heat into the night. Generally

the slab is 100-150mm thick with cost as limiting factor (Gollaway, 2004).

Timber

Concrete

Masonry withexternalCladding

15%

70%

15%

Timber

Concrete andmasonry80%

20%

Figure 3. Passivhaus construction

methods in Germany

(Source: GBM, 2009)

Figure 4. Passivhaus construction

methods in Austria

(Source: GBM, 2009)

14

The non-load bearing insulation cladding systems are attached externally. The

insulation is in the form of preformed sheets of foam plastics and is usually attached to

the wall with adhesives or mechanical anchors, as shown in Figure 5 (Balocco, Grazzini

and Cavalera, 2007).

Figure 5. Masonry wall with external cladding

Timber frame construction

Timber framed construction is based on the erection of load bearing timber frame

supporting the dead and live loads from upper floors, roofs and the timber frame wall

itself (Riley and Howard, 2002). Timber frame construction allows thick layers of

insulation to be incorporated within the frame without the need for large wall

thicknesses which take up floor space (NBT, 2009).

Figure 6 shows a typical wall cross section detail which meets Passivhaus standard of,

U-value ≤ 0.15 W/m²K. Three layers of 80mm thick insulation is used to reduce the

small thermal bridge through the timber stud, as well as increase the overall wall

insulation thickness.

15

Figure 6. Passivhaus wall detail timber construction

2.5 UK housing construction methods

Passivhaus dwellings primarily use construction techniques and knowledge common to

the country as in which they are built. The UK could indeed transfer proven Passivhaus

techniques and construction from Central European countries, however there are major

limitations to producing a successful outcome from this method. Kaan and Boer (2005)

state that Passivhaus dwellings differentiate from region to region because of the

contractors’ familiarity with construction methods, techniques and materials common in

each particular region. Williamson (2007) agrees and states that one large barrier to the

UK adopting the Passivhaus concept is the lack of skills and knowledge in the UK

concerning timber frame and masonry with external insulation construction methods.

Therefore if the UK is going to successfully adopt the Passivhaus standard on a wide

scale it will be necessary to use construction techniques, materials and methods

common to UK contractors and builders.

UK common construction methods

The English Housing Survey (DCLG, 2008) states that almost 65% of the housing

stock, as of 2008, was constructed using a traditional cavity wall structure. However

16

approximately 88% of the dwellings built post 1990 in the UK were constructed using

traditional cavity wall structure (ibid). Figure 7 shows the proportion of tradition cavity

wall structures compared to other techniques. It can be clearly seen that traditional

cavity wall structures have been the primary construction method post 1945 in the UK.

Figure 7. UK housing construction type by dwelling ages (Source: DCLG, 2008)

Therefore cavity wall structure is currently the most widely used and recognised

technique in the UK. Contractors and builders in the UK have skills in masonry cavity

wall construction, some knowledge and skills in timber framed construction and

virtually none in masonry wall with external cladding as mostly used in Germany and

Austria.

Traditional Cavity Wall Structure in the UK and other countries

The traditional cavity wall structure consists of an inner leaf of block work, an outer leaf

of masonry and a gap/cavity creating a separation between the leaves. The cavity is

typically fully or part filled with insulation to improve the thermal properties of the

17

wall, as shown in Figure 8 the inner leaf and external leaf connected using wall ties to

provide structural strength and stability.

Figure 8. Traditional cavity wall structure

The majority of the housing stock in Denmark also consists of a cavity wall structure

(PEP, 2006). Denmark has several barriers to overcome before Passivhaus dwellings

can widely spread across the country. Other countries such as the Benelux (Belgium,

Luxemburg and the Netherlands) also traditionally use cavity wall construction methods

and continue to do so for new dwellings (Hens, et al., 2007). Therefore adapting the

Passivhaus concept using cavity wall construction is not only relevant to the UK, but

also to countries such as Denmark and the Benelux.

2.7 Conclusion

The UK has the largest skill base when concerning cavity wall construction compared to

any other construction method. It has also been identified that other Northern European

countries such as Denmark and the Benelux have past and current cavity wall

construction methods.

However, it is not known whether this construction method can be successfully adapted

to meet Passivhaus standards. There is currently only one Passivhaus certified dwelling

18

in the UK which is constructed using a traditional cavity wall structure and Passivhaus

certified. This house was built by the Green Building Store at Denby Dale, West

Yorkshire (GBS, 2010a). To determine whether Passivhaus can be adapted in the UK

using traditional cavity wall structure, it is necessary to assess the construction

techniques and details used during the construction of Denby Dale which enabled the

dwelling to achieve the Passivhaus standard. Furthermore analysis on the dwelling

post-construction will provide more significant evidence as to whether cavity wall

construction is able to achieve Passivhaus standards occupied.

The next chapter sets out the methods which would be most appropriate to determine

the techniques used during Denby Dale construction to accomplish certification, and

whether the dwelling performs to the Passivhaus once occupied.

19

Chapter 3: Methodology

3.1 Introduction

Denby Dale has been identified as the only Passivhaus certified dwelling so far in the

UK built using cavity wall construction. Therefore to address the question ‘Can

Passivhaus standards be achieved using cavity wall construction in the UK?’, the

research undertaken in this dissertation is primarily geared towards the Passivhaus

certified Denby Dale dwelling. The research is split into two parts: secondary research

evaluating the construction methods and detailing of Denby Dale, and primary research;

the performance of Denby Dale since it has been occupied.

3.2 Secondary research

This section is devoted to the construction detailing and methods used in Denby Dale.

Most of the research gathered will be obtained from the building contractor (Green

Building Store, GBS) and will therefore be secondary research. The construction

detailing will be assessed at the following milestones within the build: foundations and

ground floor structure, walls structure, roof structure, windows and doors. Each section

will be assessed against the Passivhaus standard with the use of U-value calculations,

accompanied by CAD drawings to add clarity to construction detailing. Information will

also be presented as to the efforts made by GBS to obtain high airtightness at each

construction stage. This is necessary because the Passivhaus standard requires dwellings

to be tested for airtightness in order to obtain certification.

The Passivhaus standard quantifies a maximum airtightness in terms of air leakage

within a pressurised building. Therefore data obtained from blower door tests

undertaken at Denby Dale (by Leeds Metropolitan researchers) are also analysed in

relation to the Passivhaus standard.

20

Passivhaus requires a thermal bridge free construction to ensure heat loss is minimal

and it is therefore necessary to assess thermal bridging at Denby Dale. For the building

envelope junctions this will be done by analysing GBS documents. The windows

however are an important aspect when concerning heat loss and thermal bridging,

because of the complex junctions, and are a general weakness in all buildings. Therefore

the assessment of the windows will be an amalgamation of GBS documentation and the

use of THERM software. THERM software is commonly used by building and design

professionals and would therefore be an acceptable method for this dissertation. The

software will present the thermal bridges graphically and allow greater understanding of

the importance of minimising thermal bridging in Passivhaus dwellings.

3.3 Primary research

Denby Dale will be assessed as to whether, once occupied, it performs to the Passivhaus

standard. Passivhaus quantifies specific heating and primary energy demands to enable

certification. Primary data gathered by Leeds Metropolitan researchers for gas usage,

electricity usage (national grid), electricity usage (photovoltaics) and solar thermal hot

water readings will be analysed. These data will then be assessed in relation to the

Passivhaus standards for specific space heating and primary energy demand. The data

will also be used to ascertain the carbon dioxide emissions of the dwelling, when related

to fuel usage. This will be analysed and compared with existing dwellings, and relates

back to the problem specification with the UK’s targets to reduce carbon dioxide

emissions.

Additional data will also be obtained from Leeds Metropolitan researchers concerning

the external and internal environments at Denby Dale, which have been monitored using

an outdoor weather station and indoor Tiny Tag monitors.

21

The following Denby Dale data will be obtained concerning the internal temperature,

relative humidity and carbon dioxide levels, and the external temperature and relative

humidity

The main purpose of the internal data is to assess and compare Denby Dale’s

temperature, humidity and carbon dioxide with recommended levels. The external data

will be used to assess the relationship between external conditions and energy

consumption within the house. Furthermore the data will be used to investigate whether

the external environment affects the internal environment in the dwelling.

Primary research will also be conducted in the form of an interview with the Denby

Dale residents. This is necessary in order to obtain information on how the residents’

lifestyle may affect research data. Questions concerning energy usage such as cooking

and MVHR will be referred to within research findings where appropriate. The

interview will also ask subjective questions relating to comfort and the operational

aspect of living in the house. This is necessary because thermal comfort is an important

aspect which Passivhaus aims to achieve in each dwelling. CEPHEUS (2001) has

undertaken comprehensive research on a number of Passivhaus dwellings (built using

methods other than cavity wall) which also concerns the residents’ opinions. Therefore

a section will be devoted to compare the opinions of the Denby Dale residents to those

in the CEPHEUS project.

22

Chapter 4: Research Findings 1: Denby Dale construction

methods and detailing

4.1 Introduction

The Green Building Store (GBS) has built the first dwelling in the UK to achieve

Passivhaus certification using a cavity wall structure, situated in the small village of

Denby Dale. The dwelling is referred to as ‘Denby Dale’ throughout. The purpose of

this Chapter is to present research on how the dwelling has been constructed, and the

necessary detailing required to achieve Passivhaus certification. All the constructional

aspects of the Passivhaus standard and MVHR system researched in the Literature

Review (Chapter 2) will be compared with secondary research on the construction of

Denby Dale. The Passivhaus requirements are shown below in Table 4.

Table 4. Passivhaus requirements relating to construction fundamentals and

MVHR system (Source: IBO, 2008; PHI, 2011b)

Measure Passivhaus standard

Ground floor U-value ≤ 0.15 W/m²K

Walls U-value ≤ 0.15 W/m²K

Roof U-value ≤ 0.15 W/m²K

Window, frames and doors U-value ≤ 0.8 W/m²K

Window glazing U-value ≤ 0.6 W/m²K

Thermal bridging Ψ ≤ 0.01 W/mK*

Airtightness 0.6 ach @ 50 Pa**

Ventilation MVHR

efficiency ≥ 75%

* Ψ - linear thermal transmittance, refers to the additional heat loss (or gain) through the

building envelope per meter length of that detail.

**0.6 ach @ 50 Pa - air changes per hour at 50 pascals of pressure, measured using a

blower door test.

23

Secondary research on Denby Dale is gathered and compared to the Passivhaus standard

by the use of CAD cross sectional drawings, U-value calculations and airtightness

detailing. This research is used to assess the foundations and ground floor structure,

walls structure, roof structure and windows and doors at Denby Dale.

Information is also provided on first floor construction, airtightness detailing, and

thereafter the MVHR efficiency in relation to the Passivhaus standard. The linear

thermal transmittance relating to the thermal envelope of the building is summarised in

the conclusion. Thermal bridging at windows is an important factor because of the

major weakness concerning heat loss, this is analysed using THERM software.

4.2 Foundations and ground floor

The design and construction details of the foundations to ground floor are crucial for

Denby Dale to perform to the Passivhaus standard. GBS realise that all buildings

contain thermal bridges, and are impossible to eradicate; however any thermal bridges

present must be minimised through the design and materials used.

The Denby Dale cavity wall continues through to the concrete trench foundations

creating a thermal bridge. This thermal bridge allows heat to transfer from the interior,

down through the inner leaf of block work past the floor insulation, and conduct into the

ground. GBS (2010a) have minimised this thermal bridge by using lightweight aerated

7N/mm² Celcon block, which has a greater thermal resistance than dense concrete

blocks. Also 300mm thick polystyrene insulation (explained more in depth later)

extends to the concrete strip foundation to reduce the effect of the thermal bridge. GBS

(2010a, p.8) simply explain this as ‘so any heat lost from the concrete floor slab will

have a lot further to go’. Figure 9 shows a cross sectional view of the foundations and

ground floor for Denby Dale, details of which were obtained from GBS (2010a).

24

Figure 9. Denby Dale foundations and ground floor, cross section

4.2.1 Passivhaus U-value requirement comparison

For a dwelling to perform to the Passivhaus standard the U-values for walls, roof and

ground floor should be no greater than 0.15W/m2K (PHI, 2011b). Denby Dale will need

to achieve these heat transfer coefficients for each of the stated building elements, in

order to minimise heat loss and allow the building to achieve Passivhaus heating

requirements. As can be seen in Figure 9 the insulation is 225mm of Knauf polyfoam

and is installed below the concrete floor slab. The U-value through the ground floor has

been calculated in Table 5.

25

Table 5. Denby Dale ground floor U-value calculations and Passivhaus U-value

insulation requirements (Source: Bath, 2001; GBS, 2010b; Knauf, 2011c)

Layer Material

thickness (m)

Thermal conductivity

(W/mK)

Resistance

(m²K/W)

External Surface - - 0.06

Insulation (Knauf

Polyfoam floorboard) 0.225 0.033 6.82

Concrete Slab 0.100 1.130 0.09

Floor Screed 0.025 0.410 0.06

Internal Surface - - 0.12

Total Resistance - - 7.15

Overall U-value 0.14 W/m²K

Passivhaus

requirement ≤ 0.15 W/m²K

Table 5 reveals that the overall U-value for the entire cross section of the ground floor is

0.14W/m2K. This is below to the Passivhaus required heat transfer coefficient of

0.15W/m2K and therefore complies with the standard.

4.2.2 Airtightness detailing

It is important that airtightness is maintained throughout the build to ensure that once

completed the heat loss by convection is minimised. The steps taken at ground floor

level for airtight detailing are discussed here.

The hardcore was laid in 150mm compact layers, as would be the case for an ordinary

house, and a sand blinding to smooth and level off (GBS, 2010a). The 225mm of Knauf

polyfoam installed below the floor slab insulation has a damp proof membrane on top,

which consists of: damp proof membrane and reinforced steel mesh and spacer blocks,

with 100mm of concrete floor slab (ibid).

26

GBS (2010a) have used the polystyrene insulation as formwork to hold the concrete

whilst pouring, this enabling the floor to sit on top of the inner leaf block work. The

airtightness will therefore be improved by this measure as subsequent shrinkage and

cracking between floor and wall elements will have little effect (ibid).

Services

GBS (2010a) have ensured all drainage pipes protrude underneath the floor slab to

minimise thermal bridging. This can be seen in Figure 10, a photograph taken during

the construction of Denby Dale. Gas and electrical supply have to protrude through the

cavity, but airtightness is maintained by the use of grommets. The design has been well

thought through to enable sealing to take place around service pipes once the pipe has

been inserted.

Figure 10. Service penetration at ground floor (Source: GBS, 2010a)

Grommets

Pro Clima Rolflex and Kalflex grommets have been used for providing the airtightness

around service pipes at Denby Dale (GBS, 2010b). The grommets are designed to fit

and adhere around the service pipes covering diameters of 6mm-320mm, which are then

plastered over to prevent air leakage (GBS, 2010a; Pro Clima, 2011a; Pro Clima,

2011b).

27

4.3 Wall structure

The Denby Dale cavity wall is constructed from dense concrete block (internally),

insulation within the cavity consisting of three 100mm layers of Dri-Therm fibreglass

insulation batts, and 100mm of coarse natural stone on the outside (GBS, 2010a). GBS

(2010a) explains that the use of polystyrene solid closed-cell insulation within the

cavity below ground provides stability in the event of ground movement. Furthermore

the closed cell structure prevents the absorption of water. Insulation must be kept dry

because the presence of water reduces thermal performance by creating thermal

bridging (ibid).

The polystyrene foam is continued from the concrete trench foundation through to

above floor level. GBS (2010a) ensured the top of the solid polystyrene insulation was

cut at an angle to ensure any cavity water would run out through the porous external

cladding. This can be seen on Figure 11 which is an image taken during the construction

of the ground floor and cavity wall. This angle prevents the build up of water on the

impermeable polystyrene insulation which if allowed to occur would create a thermal

bridge.

Figure 11. Denby Dale cavity wall and cavity tray (Source: GBS, 2010d)

28

GBS (2010a) used Teplo ties instead of standard stainless steel walls ties. This is

because stainless steel wall ties act as a thermal bridge through the insulation due to

their high thermal conductivity. Wall structures with wider cavities also require longer

wall ties. Leeds Met (2010) research shows that steel wall ties can significantly increase

the overall U-value, deemed unacceptable for high performance cavity wall structures as

required in Denby Dale.

The Teplo tie consists of Basalt and resin, providing high strength and low conductivity

of 0.7 W/mK (as calculated to EN ISO 6946), each 450mm long, (GBS, 2010b). GBS

(2010a) claim that the Teplo ties’ low conductivity gives a nil value for heat transfer

within the PHPP. The Teplo ties are shown on Figure 12 and are installed in every two

courses of block work and three courses of Yorkshire stone cladding.

Figure 12. Denby Dale cavity wall

29

Fibreglass insulation had been chosen to ensure no gaps were present through the entire

cavity wall (solid insulation would be difficult to install and difficult to fit around wall

ties with no gaps). Avoiding gaps in the cavity wall prevents movement of air around,

behind or within the insulation, therefore thermal bypassing cannot occur (GBS, 2010a).

4.3.1 Passivhaus U-value requirement comparison

Table 6 shows the calculation of the U-value for the external wall.

Table 6. Denby Dale wall U-value calculations, with Passivhaus U-value insulation

requirements (Source: Clarke, Yaneske and Pinney, 1990; GBS, 2010b; Knauf,

2011a; PHI, 2011b).

Layer Thickness (m) Conductivity (W/mK) Resistance

(m²K/W)

External Surface - - 0.06

Masonry Outer leaf,

Yorkshire stone 0.1 1.5 0.067

Insulation - (Knauf

Dri Therm cavity slab

32)

0.3 0.032 9.375

Blockwork 0.1 1.22 0.082

2 coat Plaster 0.012 0.5 0.024

Internal Surface - - 0.12

Total Resistance - - 9.728

Overall U-value 0.10 W/m²K

Passivhaus

Requirement U-value ≤ 0.15 W/m²K

The overall U-value of the wall is 0.10 W/m

2K which comfortably meets the Passivhaus

requirement of ≤ 0.15 W/m2K.

30

4.3.2 Airtightness detailing

GBS acknowledged that achieving high levels of airtightness in cavity wall construction

is generally more difficult than in other construction methods. This is because masonry

walls allow movement of air through the material via diffusion. To overcome this

difficulty GBS (2010a) moved away from potentially leaky plasterboard with dot and

dab adhesive, but instead used wet plaster directly onto the blockwork. A two coat layer

of plaster was layered on all the walls, providing an airtight barrier.

4.4 Roof structure

The roof trusses within Denby Dale use ‘Bob Tail’ trusses with 500mm elements (GBS,

2010a), to maintain an insulation thickness of 500mm near the eaves and also enable the

insulation to be continuous. It is impossible to eliminate the repeating thermal bridge

created through the vertical timbers members supporting the roof trusses. GBS (2010a)

have instead minimised this thermal bridge by using slim (100x38mm) timber members.

4.4.1 Passivhaus U-value requirement comparison

To simplify the U-value calculation for the roof cross section, the timber fraction has

been omitted and the insulation is considered to be continuous. Table 7 shows the

materials through the cross section of the Denby Dale roof, with corresponding

thickness, conductivity and resistance for each. The overall U-value for the roof section

is 0.08 W/m2K which is almost a 50% reduction to meet the Passivhaus requirement of

≤ 0.15 W/m2K.

31

Table 7. Denby Dale roof U-value calculations, with Passivhaus U-value insulation

requirements (Source: Clarke, Yaneske and Pinney, 1990; GBS, 2010b; Knauf,

2011b; PHI, 2011b)

Layer Thickness (m) Conductivity

(W/mK)

Resistance

(m²K/W)

External Surface - - 0.06

Roof Tiles 0.027 0.83 0.03

Insulation (Knauf

loft roll 40) 0.50 0.04 12.5

OSB 0.018 0.15 0.12

Plasterboard (2

layers) 0.025 0.16 0.16

Plaster 0.003 0.50 0.006

Internal Surface - - 0.12

Total Resistance - - 13.0

Overall U-value 0.08 W/m²K

Passivhaus

requirement ≤ 0.15 W/m²K

4.4.2 Airtightness detailing

Once again it is important to make reference to measures taken at each stage of

construction when considering airtightness for a Passivhaus. The first floor ceiling was

constructed using 18mm OSB board, which is acknowledged to be airtight (GBS,

2010a). However the butted joints were sealed using Pro Clima tapes to create an

airtight structure. The OSB boards have sufficient strength to support the 500mm thick

mineral insulation in the roof (ibid). A service void was created using batons screwed in

through the OSB board. GBS (2010a) state that with the concern of airtightness the

fixings had to be screwed tight to ensure the baton clamps onto the OSB board closing

any ruptures. This detailing can be seen in Figure 13. GBS (2010a) did not introduce a

32

loft access door in the ceiling, as this would penetrate the OSB and create more

difficulties improving airtightness.

The junction between the wall and the OSB board, as shown in Figure 13, has been

sealed using Pro Clima Contenga tape, which is vapour resistant and able to bond to

plaster and timber (GBS, 2010b).

GBS (2010a) have found that the PHPP calculation methods do not incorporate

windtightness. However through past experience they have acknowledged the

importance of creating high levels of windtightness in order to reduce levels of thermal

bypass from air movement over and around insulation. GBS have increased

windtightness within Denby Dale by carrying out the following procedures, all these

approaches used can be seen in Figure 13:

1. GBS (2010a) used timber noggins between the underside of the timber trusses

and the top of the exterior stone walling. Constructional foam was applied

behind these noggins to prevent air movement into the enclosed roof (ibid).

2. The 9mm plywood airtight soffit board was screwed to the roof trussed before

the wall was complete and was also rebated into the back of the soffit board

(GBS, 2010a). Figure 13 shows this detail including the frame mastic used to

seal the junction between the soffit board and stonework.

3. Denby Dale uses a Pro Clima Solitex roof membrane, which is a vapour-open

airtight under slating membrane, therefore allowing vapour to escape from the

roof void but prevents air movement through (GBS, 2010a; Pro Clima, 2011c).

4. GBS (2010a) layered the Pro Clima Solitex roof membrane with some tension to

enable them to easily tape the overlaps using Pro Clima Tescon Profil. Timber

counter batons, running with the gradient of the roof were used to allow any

33

water which managed to pass through to the roof membrane, to easily run off

into the guttering (ibid).

5. As an extra measure GBS (2010a) the first roof membrane layer was taped to the

noggins which themselves were taped to the truss timbers.

6. Finally GBS (2010a) ran a layer of Pro Clima Tescon Profil on top of the

noggins along the whole length of the eaves.

Figure 13. Denby Dale roof and wall junction, cross section

4.5 Windows and doors

Windows and doors are usually weak spots in dwellings, because they break the

continuity of the thermal envelope and can create large thermal bridges (Leeds Met,

2010). ISO (2008) states that in a poorly insulated house 13% of heat losses can occur

from windows and doors. Furthermore, the proportion of heat lost through windows

and doors increase as a dwelling’s thermal insulation improves. It is therefore

paramount that a highly insulated building such as Denby Dale incorporates windows

with low Psi and U-values to reduce heat loss.

34

Denby Dale’s windows and doors are manufactured by Ecopassiv, and comprise a

timber frame with argon filled triple glazing (GBS, 2010c), shown in Figure 14. The

image shows how the frame is insulated using polyurethane to minimise heat loss (ibid).

Figure 14. Ecopassiv window (Source: GBS, 2010a)

4.5.1 Passivhaus U-value requirement comparison

Table 8 shows the heat transfer coefficients for the various parts of the window and the

Psi value for the junction at which the glazing meets the frame.

Table 8. Denby Dale window specifications in relation to Passivhaus requirements

(Source: GBS, 2010c; PHI, 2011b)

Component measures Heat transfer

coefficient Passivhaus requirement

Glazing Ug 0.55 W/m²K U – value ≤ 0.60 W/m²K

Head/ Jambs, Uf 0.90 W/m²K -

Sill Uf 0.97 W/m²K -

Glazing Psi Value Ψg 0.03 W/mK -

Triple glazed window U-value 0.75 W/m²K U – value ≤ 0.80 W/m²K

The Table shows that the performance of Ecopassiv triple glazed windows is better than

the Passivhaus requirement.

Polyurethane

frame insulation

Argon filled

triple glazing

35

The position of the window frame in the wall is important. Research has shown (Leeds

Met, 2010) that the lowest Psi value (W/m2K) through the junction at a window frame is

achieved when the window is positioned at the central point of the cavity insulation.

Positioning the window head closer to the inner or outer leaf of the cavity wall results in

a significant increase in the Psi value and thermal bridging for the junction (ibid). As

shown at Figure 15 Denby Dale has the windows situated within the centre of the cavity

wall insulation minimising any thermal bridges at this junction.

Figure 15. Denby Dale window detailing, plan

The window frames are supported by a permanent formwork plywood box. GBS

(2010a) acknowledged that this plywood protrudes from the thermal envelope and

would therefore create a thermal bridge. It is impossible to eliminate this thermal bridge

as the window needs some form of support. To reduce the effect of the thermal bridge

GBS (2010a) ensured the plywood box only extended halfway through the cavity. This

can be seen in Figures 15 and 16. Furthermore insulation was then able to be wrapped

around the ends of the plywood box and also the window frame, again reducing areas of

thermal bridges.

36

4.5.2 Airtightness detailing

GBS (2010a) sealed the junction between the plywood box and blockwork using Pro

Clima airtightness tape. These tapes (shown in red Figures 15 and 16) are then plastered

into the blockwork creating an airtight seal. Preformed aluminium was used to close the

cavity which would otherwise expose the cavity insulation and allow unwanted air

movement through the insulation (ibid).

Figure 16. Denby Dale window detailing, cross section

4.5.3 Thermal Bridging, THERM analysis

An effective way of indentifying thermal bridging within buildings is by incorporating

CAD drawings within freely available software such as THERM and WINDOW. The

37

CAD drawings are used as an underlay, so the outline can then be recreated using

drawing tools within THERM. Figure 17 Shows a window junction within Denby Dale

drawn in the THERM (v.6) software. Each block colour represents a particular material

and corresponds to the properties of that material within the software. WINDOW (v.6)

software has been used to create the glazing which holds the corresponding data

required by THERM to complete the calculations. WINDOW software is compatible

with THERM so the Denby Dale glazing file is transferred across, and the glazing can

then located into the window frame. Boundary conditions are then assigned to the

internal and external boundaries.

Figure 17. Denby Dale window junction, isotherms produced in THERM

(Source: Author)

Figure 18 (below) shows exactly the same window junction however presented in

thermal infrared. The external and internal temperatures computed in THERM are -18˚C

and 21˚C. The 300mm thick Knauf insulation is shown to be highly effective at

preventing heat loss from the building, because Figure 18 shows the internal surface

temperature to be close to 21˚C, which is near to the internal air temperature. The triple

38

glazed argon gas Ecopossiv windows show a surface temperature exceeding 17˚C,

therefore proving successful in reducing heat loss from the building.

Figure 18. Denby Dale window junction, colour infrared produced in THERM

(Source: Author)

GBS (2010c) states that the glazing psi value (Ψg) in the Ecopassiv window is 0.03

W/mK, which is shown graphically in Figure 19. As typical with all windows Figure 19

shows the most significant thermal bridges occur at the glazing to frame junction and

the frame to frame junction. This is an inevitable weakness in the thermal envelope at

each of these junctions, which must be minimised as much as possible to achieve high

performance.

39

Figure 19. Denby Dale window junction, colour flux magnitude produced in

THERM (Source: Author)

Figure 20 shows graphically how the thermal bridge is transferring heat through the

glazing to frame junction. Heat flux vectors are defined by Fourier’s Conduction Law,

which multiplies the thermal conductivity of a material by the temperature gradient

(Akin, 2010). Therefore as the temperature gradient becomes greater between internal

and external boundaries, the thermal bridge will cause greater heat loss via conduction.

Figure 20. Denby Dale window junction, flux vectors produced in THERM

(Source: Author)

Ψg = 0.03 W/mK

40

The cause of the weakness within this window, as with most other windows, is the

rubber sealant around the edge of the glazing, which creates a thermal bypass through

the frame insulation and the argon filled glazing. However the thermal bridging from

glazing to frame junctions, in this Ecopassiv window, achieve Ψg 0.03 W/mK, which is

significantly lower than standard windows. PHPP (2007) states that windows that have

Ψg 0.05 W/mK are still acceptable for use in Passivhaus dwellings. Therefore the

overall window (including U-values and thermal bridging) reduces heat loss sufficiently

to be accepted by Passivhaus.

4.6 First floor junction and airtightness detailing

Denby Dale uses a 302mm deep I-Beam system for the first floor, illustrated in Figure

21. Particular attention has been paid to the junction, where the floor meets the inner

blockwork leaf (GBS, 2010a). The I-beam floor joists do not protrude into the wall as

with usual house construction as this would lead to air leakage from the expansion and

shrinkage of the timber (ibid). Instead a 45mm/ 302mm laminated timber wall plate was

fixed to the blockwork. Prior to this the block work was parged with a sand and cement

mix to improve airtightness behind the wall plate. The wall plate was fixed using

stainless steel threaded bars with washers and nuts and taken 75mm into the 100mm

blockwork (ibid). Epoxy resin was also applied in the holes to act as a further airtight

barrier. The I-beam joists are attached to this wall plate with steel hangers. To further

improve airtightness GBS (2010a) claims to have masticked the top and bottom of the

wall plate using Pro Clima Orcon F.

41

Figure 21. Denby Dale first floor junction, cross section

4.7 Airtightness testing

In order for a house to be Passivhaus certified, an airtightness of below 0.6 ach @ 50 Pa

must be achieved. A blower door test is used to measure the airtightness of a building,

which consists of sealing a fan to an exterior door, as shown in Figure 22. Passivhaus

requires that all airtightness tests are undertaken in accordance to DIN EN 13829, which

comprises a series of over pressurization and under pressurization tests (PHPP, 2007).

The test is carried undertaken at areas of the building which involved the heated

building envelope, therefore does not include loft and garage areas.

Figure 22. Blower door airtightness test (Source: GBS, 2010a)

42

The blower door test was first undertaken on 14/01/2010, during construction, by Leeds

Met University researchers. This enabled any airtightness weaknesses to be remedied

before fully constructing the building (GBS, 2010a). The depressurisation and

pressurisation caused by the fan, forces air in and out the building, the amount of which

is measured using a DG 700 Gauge. The initial results are shown in Table 9.

Table 9. First Denby Dale blower door test results (Source: Leeds Met University)

Mean Flow @ 50Pa = 113.92 m3/h

ACH50 = 0.38 ach

Air Permeability at 50 Pa = 0.41 m/h

The air permeability is calculated from the mean flow of air at 50 Pa (the amount of air

flowing out of the building per hour, from 50Pa of pressure), which is divided by the

internal volume on the building, which is 277m3 (GBS, 2010a).

To conclude the blower door test, a smoke test was carried out to pinpoint any

vulnerable areas allowing air leakage. After GBS (2010a) rectified some of the Pro

Clima Tescon Profile tape the test was repeated and the result was an airtightness of

0.33 ach @ 50Pa, well within the Passivhaus limit of 0.6 ach @ 50 Pa.

4.8 Mechanical ventilation and heat recovery system (MVHR)

Ventilation is important in a Passivhaus dwelling to maintain internal temperatures and

supply good indoor air quality to the occupants (Passipedia, n.d).

The MVHR system installed in Denby Dale is a Paul Thermos 200 unit (GBS, 2010a),

which is shown in Figure 23.

43

Figure 23. Denby Dale MVHR system

This MVHR unit has been certified by the Passivhaus Institute (PHI) with a recorded

efficiency of 92% (Paul, 2009), with further claims that the efficiency of this MVHR

system can reach up to 94%. This is well within the Passivhaus requirement of ≥75%

efficiency.

4.9 Summary

The exterior building elements (roof, walls ground floor) have achieved overall design

heat transfer coefficients less than 0.15 W/m2K and are therefore considered acceptable

within Passivhaus standards. Passivhaus require that thermal bridges at junctions within

the thermal envelope must not exceed Ψ ≤ 0.01 W/mK, GBS (2010a) state that during

the design process with the aid of PHPP the thermal bridges in the thermal envelope

were no more than Ψ ≤ 0.01 W/mK, which is acceptable for Passivhaus.

The overall U-value for the window, which includes the glazing and the frame, is 0.75

W/m2K. This figure does not exceed 0.8 W/m

2K and therefore is within Passivhaus

requirements. The thermal bridging occurring at the windows, as demonstrated using

44

THERM software, has more leniency than thermal bridging within the thermal

envelope. GBS (2010c) states that the Ecopassiv windows achieve a glazing psi value of

(Ψg) 0.03 W/mK and installation Ψ of - 0.004 W/mK. PHPP (2007) gives examples of

psi values acceptable for windows in Passivhaus dwellings of 0.00-0.05 W/mK.

Therefore the windows used in Passivhaus dwellings would be deemed acceptable.

The blower door test shows the result of all the airtightness detailing undertaken during

each construction phase. GBS (2010a) states that the house achieved 0.33 ach @50Pa

which is better than the Passivhaus requirement by 45%.

Finally the MVHR system must have an efficiency rating of no less than 75% to be

acceptable. The Paul Thermos 200 unit achieved way in excess of this of 92% and is

therefore within the Passivhaus requirement.

45

Chapter 5: Research Findings 2: Denby Dale

performance

5.1 Introduction

It has been found that the dwelling’s cavity wall construction and MVHR system meet

the Passivhaus requirements. This Chapter will use research data obtained from Denby

Dale by Leeds Metropolitan researchers who have monitored the dwelling since

construction on energy consumption, internal and external temperature, and indoor air

quality, to evaluate whether the in-use performance of the dwelling meets Passivhaus

requirements. Reference is also made to the interview questions and answers from the

homeowners where relevant to the analysis of the data.

CEPHEUS research, conducted on 221 Passivhaus dwelling units, has shown average

results of reduced heating requirements of 80% compared to legal standards

(Schnieders, 2003). The project also revealed total averaged primary energy

consumption to be less than 50% of that of conventional new buildings.

Schnieders (2003) states that the idea of the CEPHEUS project was to demonstrate the

technical feasibility of different building construction techniques across various

countries. However the construction methods involved in the project were variations of

timber frame, masonry with external cladding and pre cast concrete construction

methods. None of the buildings monitored was of cavity wall construction. It is

therefore necessary to assess the data relating to Denby Dale to see if cavity wall

construction is able to compare to proven techniques when related to Passivhaus

requirements. The analysis of the data will give an indication to how well UK building

techniques can compare with the German low energy Passivhaus specifications.

46

Analysis is presented of the primary energy demand, carbon dioxide emissions, space

heating requirements, internal and external temperatures and humidities.

5.2 Primary energy demand

CEPHEUS (2001) states that primary energy (PE) demand consists of the sum of energy

requirements for space heating, domestic hot water and household appliances.

Passivhaus requires that the Specific Primary Energy Demand (SPED) should not

exceed 120 kWh/(m2/a), therefore it is necessary to assess energy usage data for Denby

Dale over an annual period.

Denby Dale energy consumption consists of gas usage (boiler and gas hob), and

electricity consumed (electrical appliances and lighting). Initially electricity was

provided from the national grid. However photovoltaic (PV) panels were installed in

February 2011, so the dwelling now generates its own renewable electricity as well as

exporting from the national grid. The PV panels are installed on the south-facing roof

section, as can be seen in Figure 24. Solar thermal hot water (STHW) was also

introduced to the house in March 2011, therefore the DHW demand is supplied by a

combination of STHW and gas boiler.

Figure 24. Denby Dale south elevation

47

The data has collected by Leeds Metropolitan University researchers comprises meter

readings from gas, electricity, generated electricity (PV) and STHW readings.

Table 10 shows the average annual energy usage (kWh) from, 05/01/2011 to

05/01/2012. The gas consumption for the period of 14/03/2011 to 17/04/2011 was

unrecorded because the dwelling awaited a replacement gas meter. For the purpose of

calculating PE demand for the annual period, a daily average of 6.82 kWh has been

used for this period (the consumption rate for the same period of the previous year),

value is highlighted yellow in Table 10. Table 10 shows the values of the final energy

demand (Qfinal) for Denby Dale, consisting of, gas, STHW, electricity imported and

electricity generated. The overall final energy demand for the annual period is 9366.7

kWh.

Schnieder (2003) states that research undertaken during the CEPHEUS project

concerning primary energy consumption, included only non-renewable sources of

energy to the dwellings. For example ‘energy consumption for hot water provided

directly by a solar thermal installation is not included in the final energy consumption

for the household’ (Schnieder, 2003, p347). PHPP (2007) also deducts solar thermal

energy when providing PE calculations. Therefore the renewable energy supplied by

STHW at Denby Dale is not included within the calculation. Photovoltaics are also a

non renewable energy source and are not included within this calculation.

48

Date of Reading Gas (kWh)

Electric

units

imported

(kWh)

Electricity

generated

(kWh)

STHW

(kWh)

Total Primary

Energy Usage for

the period

05/01/2011 - - - - -

02/02/2011 914.9 188.0 33.0 - 1135.9

14/03/2011 871.5 232.8 77.6 119.0 1300.9

17/04/2011 232.1 154.5 140.9 357.0 884.5

07/05/2011 51.8 77.7 99.5 270.0 499.0

25/05/2011 16.0 72.0 109.0 192.0 389.0

27/06/2011 37.2 120.9 182.6 341.0 681.7

01/08/2011 35.6 132.5 178.7 336.0 682.8

01/09/2011 22.1 131.0 129.7 345.0 627.8

01/10/2011 25.3 176.0 120.0 175.0 496.3

02/11/2011 229.6 190.2 82.1 141.0 642.9

11/12/2011 462.8 209.4 32.3 - 704.5

02/01/2012 967.5 270.6 25.9 - 1264.0

05/01/2012 67.5 0.0 0.0 - 67.5

Total annual consumption from: 5/01/2011 to 5/01/2012 Overall Final

Energy Demand

(kWh)

Final Energy Demand

(Qfinal) 3933.8 1955.6 1211.3 2276.0 9376.7

Average daily use 10.8 5.3 3.3 - 25.1

Table 10. Denby Dale annual energy usage, with Passivhaus requirement in relation to primary energy demand

49

To convert the final energy demand into primary energy demand the following formula

is used (PHPP, 2007):

QP = p ∙ Qfinal

Where:

p: non renewable primary energy factor of the energy source

Qfinal: Final energy demand

5.2.1 Comparison to Passivhaus requirement

Table 11 shows the input of Denby Dale energy consumption, primary energy factor

and the calculation from the above formula.

Table 11. Denby Dale primary energy demand calculation

Energy

Source

Primary Energy

Factor (kWh)

(PHPP, 2007)

Denby Dale Usage: 5th

Jan

2011 to 5th

Jan 2012

(kWh)

Primary Energy

Demand (kWh)

Natural gas 1.1 3933.8 4327.2

Electricity 2.7 1955.6 5280.1

Primary Energy Demand

(kWh) 9607.3

Specific PE demand

[kWh/(m2a)]

92.0

Table 11 shows the total primary energy demand to be 9607.3 kWh for the annual

period. The SPED is the PE demand per square meter of treated floor area and is 92.0

kWh/(m2a), well within the PH requirement of 120 kWh/(m

2a).

5.3 Carbon dioxide (CO2) emissions

Now that the PE demand has been determined, the GHG emissions can be calculated.

For this process all 6 greenhouse gases (CO2, CH4, HFCs, PFCs, PFCs and N2O) are to

50

be factored as CO2 equivalent emissions, related to their global warming potential

(PHPP, 2007; UNFCCC, 2008).

This is done for each energy source. The release of annual and specific CO2e emitted

can be calculated by the following formula (PHPP, 2007):

Where:

: Specific CO2 – equivalent CO2 emissions [kg/(m2a)]

: Annual CO2 – equivalent CO2 emissions [kg/a]

: CO2 equivalent emissions factor [kg/kWh]

: Energy Usage [kWh]

ATFA: Treated floor area [m2]

Denby Dale uses non-renewable sources of energy in the form of natural gas and

electricity. The PV panels and STHW do not contribute to CO2e emissions and are

therefore not included in this calculation. However the PHPP (2007) uses a PV

electricity CO2e savings factor of 0.25kg/kWh and is therefore deducted. Table 12

shows the sum of natural gas and electrical usage within Denby Dale, which is

multiplied by the CO2e emission factor ([DIN V 4701-10], [Gemis]; standard April

2004, cited in PHPP, 2007).

51

Table 12. Primary energy usage and PHPP CO2 emission factors

Energy

Source

PHPP CO2e

emission factor

(kg/kWh)

Denby Dale Usage: 5th

Jan 2011 to 5th

Jan 2012

(kWh)

Annual CO2e

emissions

(kg/a)

Natural gas 0.25 3933.8 983.5

Electricity 0.68 1955.6 1329.8

PV-electricity

(savings) 0.25 1211.3 -302.8

Annual emissions

[kg/a]: 2010.5

Specific CO2e emissions

[kg/(m2a)]

19.3

The emission factors vary according to the source and also over time periods. The SAP

(2009) carbon dioxide emission factors are used in the UK. Table 13 shows the same

calculation method but with the SAP carbon dioxide emission factors. PV electricity

CO2e emission savings factor are referred to in SAP (2009) as electricity displaced from

grid, with a figure of 0.527 kg/kWh.

Table 13. Primary energy usage and SAP CO2 emission factors

Energy

Source

SAP CO2e emission

factor (kg/kWh)

Denby Dale Usage: 5th

Jan 2011 to 5th

Jan 2012

(kWh)

Annual CO2e

emissions

(kg/a)

Natural gas 0.198 3933.8 778.9

Electricity 0.517 1955.6 1011.0

PV-electricity

(savings) 0.527 1211.3 -638.4

Annual emissions

[kg/a]: 1151.5

Specific CO2e emissions

[kg/(m2a)]

11.0

The result shows that there is a 42% difference between the specific CO2e emissions

calculated using PHPP and SAP. SAP gives lower CO2e emissions for Denby Dale

because of the lower emission factors. It is important to acknowledge both of these

52

results because PHPP is representative for Passivhaus for which Denby Dale is based

around, and SAP is most widely used within the UK which is likely to be more accurate

when referring to a UK dwelling. These figures can now be related to UK building

regulations.

5.3.1 Comparison of SAP and PHPP factors

DCLG (2009) estimates that to comply with Part L1A, dwellings must not emit more

than 43.5 kgCO2e/m2

annually. Figure 25 provides a comparison of Denby Dale’s

performance (SAP and PHPP emission factors) in relation to UK building regulations

and typical Passivhaus CO2e emissions (ibid).

Figure 25. Comparison of carbon dioxide equivalent emissions produced from

primary energy usage (Source: DTLR, 2010; Hardi, 2011)

Figure 25 indicates that Denby Dale, when using PHPP CO2e emission factors,

achieved a reduction of 56% in emissions compared to the ADL1-2010 building

regulations. This reduction, however, is greater when SAP CO2e emission factors are

used, resulting in a 75% decrease on the ADL1-2010 building regulations. Even though

the calculations use different emission factors which results in a difference of 42%, each

0

10

20

30

40

50

60

70

80

UK Dwelling

Stock

ADL1-2010

UK Building

regs

Typical

Passivhaus

Denby Dale

PHPP Factors

Denby Dale

SAP Factors

CO

2e

emis

sion

s (k

g/(

m²a

)

53

method has shown that Denby Dale has by far exceeded the 2010 building regulations.

Figure 25 also shows that Denby Dale is performing below that of typical Passivhaus

dwellings when regarding CO2 emissions.

5.4 Space heating demand

Passivhaus dwellings require space heating energy demand to not exceed 15

kWh/(m2/a). In order to calculate the space heating requirement the heating system and

type of energy used for space heating needs to be identified. GBS (2010a) states that the

space heating system at Denby Dale is run entirely from the gas Vaillant boiler, which

is connected to the following components: as duct heater in the MVHR system (to heat

ventilation supply air), one radiator in the living room and two towel rails (also include

electric heating elements). GBS (2010a) also acknowledged that the residents may

require the towel rails to provide heating on demand to dry clothes. To resolve this GBS

installed electric heating elements within the towel rails. However the interview with

the residents, (Question 7) revealed that they did not use the electric heating elements as

the MVHR system provided sufficient heat for drying. Therefore no electricity has

contributed directly towards space heating, and is being entirely provided from the gas

boiler. The gas boiler uses energy to supply demand for domestic hot water (DHW)

which will also have to be deducted from the gas usage in order to calculate the energy

used for space heating. Furthermore the gas usage (kWh) in Table 14, will also include

gas used from the gas cooker, this will have to be deducted in order to finalise the

energy demand for space heating.

Gas used for Domestic Hot Water

The residents installed solar thermal hot water (STHW) panels on the south-facing roof

section of the house that came into operation on 3 February 2011; this information is

shown in bold in Table 14. All hot water was provided from the STHW panels from

54

20/3/11 to 13/9/11. During this period the boiler was switched off, so the amount of

energy used to supply DHW demand can be estimated from the STHW energy

generated.

Table 14. Gas energy usage and solar thermal readings, required for annual DHW

estimation (Source: Leeds Met University)

Date of

Reading

Days since

last reading Gas (kWh)

STHW

(kWh) Notes

02/02/2011 - - - -

14/03/2011 40 871.5 119.0 boiler off all MM all Hot

water from Sun

17/04/2011 34 232.1 357.0 Boiler off all dMMw All

hot water from Sun

07/05/2011 20 51.8 270.0 boiler off all MME all

hot water from Sun

25/05/2011 18 16.0 192.0 boiler off all the time

27/06/2011 33 37.2 341.0 boiler off all the time

01/08/2011 35 35.6 336.0 boiler off all the time

01/09/2011 31 22.1 345.0 Boiler off from 20.3.11

all hot water from sun

FIT 1871.8 13.9.11

01/10/2011 30 25.3 175.0 boiler off all the time

02/11/2011 32 229.6 141.0 boiler on 12-10-11

As shown in Table 14, the demand for energy to heat water in the period of 20.3.11 to

13.9.11 amounts to 1871 kWh (total of 177 days). The average daily energy used for

DWH is therefore 10.6 kWh. To determine the accuracy of the average daily gas usage

for DHW of 10.6 kWh, Figure 26 shows the average daily energy consumption and

generation. Between the period of 04/05/2011 and 04/10/2011 all hot water is provided

by STHW and therefore the daily average can be based around the STHW readings.

Figure 26 shows that a daily average of 10.6 kWh is a reasonable estimation for energy

required for DHW.

55

Figure 26. Denby Dale average daily energy consumption and generation

0

10

20

30

40

50

60

70

En

ergy i

n k

Wh

Average Daily Energy Consumption/ Generation

Mains Gas Consumed

Electricity Generated by PV

Electricity imported from grid

Solar Thermal Hot Water heat

generated

Average gas usage for DHW

approximately: 10.6 kWh

56

Therefore applying this figure to the remaining days of the year (188) gives a figure of

1992.8 kWh (from the previous 1871 kWh for 177 days). This figure can be deducted

from overall gas usage because it does not contribute towards demand for space heating.

Gas usage for Cooking

Before the specific space heating demand can be determined, the gas usage for cooking

also needs to be estimated and then deducted. Table 15 shows gas energy usage from

08/05/2011 to 01/10/2011. During this period the boiler is off all the time, because

space heating demand and DHW demand is met from alternative sources. The gas

energy usage is therefore for cooking applications (gas hob).

Table 15. Gas energy usage, solar thermal readings and boiler switched off,

required for annual gas cooking estimation (Source: Leeds Met University)

Date of

reading

Days since last

reading Gas (kWh)

STHW

(kWh) Notes

07/05/2011 - - - -

25/05/2011 18 16.0 192 boiler off all the time

27/06/2011 33 37.2 341 boiler off all the time

01/08/2011 35 35.6 336 boiler off all the time

01/09/2011 31 22.1 345 Boiler off from 20.3.11

all hot water from sun

FIT 1871.8 13.9.11

01/10/2011 30 25.3 175 Boiler off

Total 136.2

The average daily gas usage for cooking over the 147 day period is therefore 0.9 kWh.

To determine the accuracy of the average daily gas usage for cooking of 0.9 kWh,

Figure 27 shows the average daily energy consumption and generation. Between

04/05/2011 and 04/10/2011 all hot water is provided by STHW which leaves an

averaged gas used for cooking within the dwelling.

57

Figure 27. Denby Dale average daily energy consumption and generation

0

10

20

30

40

50

60

70

En

ergy i

n k

Wh

Average Daily Energy Consumption/Generation

Solar Thermal Hot Water heat

generated

Electricity Generated by PV

Electricity imported from grid

Mains Gas Consumed

Average gas usage for cooking

approximately: 0.9 kWh

58

Figure 27 shows that a daily average of 0.9 kWh is an accurate representation for

cooking gas usage. Therefore the annual estimate for cooking gas usage is 328.5 kWh.

5.4.1 Comparison to Passivhaus requirement

The space heating demand can be ascertained by deducting DHW and cooking from the

overall gas usage:

Total gas usage not specified to space heating = 328.5 + 1992.8 = 2321.3 kWh

Total annual space heating demand = 3933.3 – 2321.3 = 1612.5 kWh

Specific space heating demand = 1612.5/104.4 = 15 kWh/(m2/a)

The specific space heating demand is within the Passivhaus requirement of 15

kWh/(m2/a).

5.5 Distribution of energy use

The components which contribute to specific energy consumption can now be

identified. Figure 28 shows the breakdown of specific energy consumption.

Figure 28. Specific energy consumption

0

10

20

30

40

50

60

70

80

90

100

Denby Dale

PE

kWh

/(m

2 /a)

Cooking (Gas)

Electricity generated

Space Heating (Gas)

DHW (Solar)

Electricity imported

DHW (gas)

59

It can be seen that the energy demand for hot water has had the largest contribution to

Denby Dale’s PE consumption, approximately 44%. Space heating demand has

contributed around 21% of total PE demand, more than half of that of DHW. In

comparison to current UK housing, the DECC (2011a) states that approximately 58% of

PE consumption is used for space heating, and DHW accounts for 29%. Therefore

Denby Dale has significantly reduced requirement for space heating demand. In order to

quantify this improvement, Figure 29 shows specific PE demand for the UK dwelling

stock 2006, compared to Denby Dale PE demand.

Figure 29. Comparison of primary energy consumption: Denby Dale and UK

homes (Source: AECB, 2006)

Figure 29 shows a comparative PE performance difference of 183 kWh/(m2/a),

amounting to a 74% increased energy efficiency at Denby Dale. The most dramatic

difference can be seen with the specific space heating demand, as Denby Dale boasts a

90% improvement on the UK dwelling stock. This is largely due to the construction

detailing and an unbroken insulation layer free from thermal bridges and high level of

airtightness.

0

50

100

150

200

250

300

UK Dwelling Stock

baseline 2006

Denby Dale

PE

kW

h/(

m2/a

)

Cooking (Gas)

Electricity generated

Space Heating (Gas)

DHW (Solar)

Electricity imported

DHW (gas)

60

5.6 Indoor carbon dioxide (CO2) levels

The level of CO2 in Passivhaus dwellings is not a requirement for certification.

However high concentrations of CO2 can reduce comfort within a building and

residents’ comfort and air quality are important Passivhaus concepts. It is therefore

important to determine whether the CO2 levels at Denby Dale are at an acceptable level.

CIBSE recommends a CO2 concentration of no more than 900ppm to control human

odours and maintain comfort, and anything in excess of 1000ppm reduces human

comfort and air quality (Dearden, 2011). Assuming that outdoor CO2 levels are

approximately 400ppm, the fresh air supply rate within a home should not fall below

8l/s per adult occupant. At this rate of ventilation, the upper limit of 1000ppm CO2

concentration would not be exceeded (ibid).

CO2 levels within the Denby Dale dwelling have been measured using Tiny Tag

monitors. These monitors measure and store the data at daily intervals which can then

be downloaded onto spread sheets, all of which has been conducted by Leeds

Metropolitan Researchers. The Tiny Tag monitors have provided measured CO2 levels

in the lounge and bedroom. The results from 20/07/2010 to 06/01/2012 are shown in

Figure 30. From 28/06/2011 to 21/09/2011 there was a period of unmonitored data, due

to full data loggers. This section will therefore be assumed to follow the typical trend of

the data.

The CO2 concentrations are largely influenced by the ventilated air from the MVHR

system, and are a good indicator of how efficiently the system is working. There seems

to be an increased control of the CO2 levels throughout the time period monitored, as

differences between the lounge and bedroom are reduced. This could possibly be

explained by the residents’ response to Question 11, in the interview. The residents

admit that it took time to finely tune and adjust the MVHR system to optimise output.

61

Figure 30. Denby Dale daily average CO2 concentrations (Source: Leeds Metropolitan University)

0

200

400

600

800

1000

1200

1400

1600

1800

CO

2 C

on

cen

trati

on

in

pp

m

Daily Average CO2 Concentrations

Lounge

Bedroom

62

From the period of 20/07/2010 to 20/12/2010, when most drastic fluctuations occur, the

residents were likely to be changing the quantity of ventilated air on the settings more

frequently as they adjust the settings to their liking.

An unusual feature of the data in Figure 30 is that CO2 concentrations in the lounge are

generally higher than in the bedroom, especially between the most recent period of

20/09/2011 to 5/01/2012. Table 16 quantifies this finding, as the lounge produces a

range of 1415ppm CO2 concentration, compared to 999ppm for the bedroom. Also the

CO2 concentrations in the lounge are on average higher than in the bedroom. It is

generally found that bedrooms produce higher levels of CO2 concentrations because of

the length of time people are sleeping in these rooms (Koiv, et al., 2010). The open plan

internal layout of the building could provide a possible answer to this unusual result.

The Denby Dale first floor plan (Figure 43 in Appendices 4.0) shows that both

bedrooms are located next to the small atrium. The atrium provides a sense of open

space and also allows sunlight to filter through to the back of the building. The atrium

also allows large amounts of air movement between the bedrooms and the lounge

below. CO2 is denser than most of the other constituents of air, so the atrium could be

allowing CO2 to pass from the bedrooms on the first floor, at night, down to the lounge

on the ground floor. This would cause a decrease in bedroom CO2 readings and an

increase in lounge CO2 readings, and account for the results in Table 16.

Table 16. Denby Dale CO2 levels (ppm) from 20/07/2010 to 06/01/2012

Lounge Bedroom

Range min 240 339

Range max 1655 1339

Average 712 658

Overall Average (ppm) 685

63

Other Explanations for high readings

Table 17 presents the highest monitored data in both the lounge and bedroom, all of

which are considered higher than required in order to maintain comfort (Dearden,

2011). Some reasons why these measurements could have occurred are as follows:

- The MVHR system uses filters to clean incoming air. If the filters are not

changed frequently, fresh ventilation rates can be reduced as the filters become

clogged up. The CO2 concentrations increase as the small quantity of fresh

incoming air provides little dilution.

- The number of people present in the house. The residents have held Passivhaus

conferences and meetings at Denby Dale. The MVHR system is designed to

ventilate air into the house for around 2 -3 people. A greater number of people

inside the building would cause a dramatic rise in CO2 which the MVHR system

would not be able to remove at a sufficient rate. The higher CO2 levels in the

lounge compared to the bedroom would give credence to this explanation as

people more likely to socialise within the lounge area.

Table 17. Highest average CO2 concentrations measured within Denby Dale

(Source: Leeds Met University)

Lounge

Bedroom

Date

Average CO2

concentrations (ppm) Date

Average CO2

concentrations (ppm)

03/10/2010 1169

15/04/2011 1213

28/12/2010 1175

25/12/2010 1253

31/08/2010 1244

11/11/2011 1306

11/11/2011 1389

14/04/2011 1339

14/04/2011 1655

26/12/2010 1369

64

Other Explanations for low readings

Table 18 presents the lowest monitored data in both the lounge and bedroom. Low CO2

readings are not a problem within a household; they generally mean the air quality is

better. However there must be some reason why the indoor CO2 at Denby Dale dropped

to this level.

Table 18. Lowest average CO2 concentrations measured within Denby Dale

(Source: Leeds Met University)

Lounge

Bedroom

Date

Average CO2

concentrations (ppm)

Date

Average CO2

concentrations (ppm)

08/08/2010 240 09/10/2011 275

07/08/2010 276 15/05/2011 287

29/10/2010 290 24/04/2011 298

28/10/2010 292 25/04/2011 304

27/10/2010 304 01/05/2011 314

When an interview was conducted with the Denby Dale residents (Question 11), they

stated that they opened windows whenever they feel the need to, in both summer and

winter seasons. This could explain why some CO2 readings have fallen as low as

240ppm. The majority of these low readings have occurred out of winter season, and

therefore the residents are more likely to open windows in warmer periods, creating

sudden influxes of fresh air.

However this would not explain the sub 350ppm of CO2 typical of outdoor air quality as

stated by Dearden (2011). Prill (2000) acknowledges that outdoor CO2 levels differ

from place to place due to the amount of CO2 producing activities in the areas e.g.

traffic, manufacturing etc. The Denby Dale dwelling is situated in a small West

Yorkshire village. The activities which take place in the village would be less likely

65

produce CO2 emissions than in a city. Therefore if the external air has naturally lower

CO2 concentrations, when the residents open the windows it is likely to reduce the CO2

in the dwelling.

5.7 Internal temperature

PHI (2011a) states that Passivhaus dwellings are usually maintained at around 20°C.

There is no specific internal temperature required to be met for Passivhaus certification.

However the Passivhaus philosophy states that dwellings must provide thermal comfort

for occupants. Thermal comfort and internal temperature will be assessed by analysis of

temperature readings and the residents’ own opinion.

The internal temperatures were recorded using Tiny Tag monitors placed in the kitchen,

lounge, bedroom, study and bathroom. External temperatures were recorded by a small

weather station in the garden; both of these sets of data were collected by Leeds Met

University researchers. Figure 32 shows a graph for the internal temperatures and

external temperature from the period of 20/07/2010 to 06/01/2012, which was also

compiled by Leeds Met University researchers. Also from the period of 28/06/2011 to

21/9/2011 there is unmonitored data, due to full data loggers.

As can be seen from Figure 32 the indoor temperature mostly falls within the 20°C to

25°C range. This is similar to the findings of the CEPHEUS project, as Schnieders

(2003) states that indoor temperatures within the 221 Passivhaus dwellings rarely rose

above 25°C. This observation implies that temperature within a cavity wall structure is

able to be controlled as well as dwellings built using proven Passivhaus construction

methods.

Between 20/11/2010 and 20/02/2011 there were greater fluctuations of the indoor

temperature. The bedroom temperatures are generally consistently high, almost reaching

66

29°C at one point. The kitchen area has the recorded lowest internal temperatures,

creating an average difference between bedroom and kitchen temperatures of 4-5°C.

This maybe explained from the setup of the MVHR system, because the heated supply

air is ventilated into the bedrooms, lounge and study area. Therefore when the heating

system is on during the winter period the rooms are likely to see a rise in temperature.

This corresponds to Figure 31 where the blue pipe represents the supply ducting. The

kitchen area does not receive any heated supply air but instead incorporates an

extraction duct, shown as red piping in Figure 31 representing the extraction ducts. As

the kitchen does not directly receive heated air it can therefore be expected that the

temperature would be lower than that of the bedrooms.

Figure 31. Denby Dale ventilation ducting (Source: GBS, 2010a)

Figure 32 corresponds with interview Question 11, as the residents stated that some

overheating occurred during the winter. This is unusual as the overheating has occurred

during cold winter temperatures, indicating the cause is most likely to be the heating

system. During this period the residents did not experience thermal comfort as would be

expected for a Passivhaus dwelling. However they explained that it has taken time to

adjust the settings to a comfortable temperature.

67

Figure 32. Denby Dale daily average temperatures external and internal (Source: Leeds Met University)

-10

-5

0

5

10

15

20

25

30

35

Tem

per

atu

re (

ᵒC)

Denby Dale Daily Average Temperatures

External

Kitchen

Lounge

Study

Bedroom

Bathroom

68

Post 20/02/2011 the internal temperatures in Figure 32 show more control and

consistency, mostly within the range of 21°C to 24°C. The average internal temperature

from 20/02/2011 is approximately 22°C, which the residents felt was comfortable for

their preferences as they have adjusted the MVHR system to their liking. In comparison

to the CEPHEUS project Schniders (2003) states that the mean room temperature

during the heating period was 21.4°C.

PHI (2010) states that the frequency of temperatures higher than 25˚C should occur no

more than 10% of the time. Between 20/07/2010 and 05/07/2012, 2230 daily averaged

data were monitored in the kitchen, lounge, study, bedroom and bathroom. Over this

period the daily average exceeded 25˚C on 87 occasions. This amounts to less than 4%

and therefore the dwelling has performed to the PHI recommendations.

5.8 Internal relative humidity

Relative humidity (RH) is an important factor in thermal comfort. EPA (2006) states

that as RH rises, the ability to lose heat through perspiration and evaporation reduces,

having a similar effect to raising the temperature. Extremes of RH will cause

discomfort. RH above 70% will promote the growth of mould and mildew, and levels

around 25% can cause someone to have a dry throat and nose (Lstiburek, 2002; Oozawa

et al., 2012)

A typical Passivhaus dwelling normally achieves RH levels of approximately 50% (IBO

2008). RH has been monitored at Denby Dale by the use of Tiny Tag monitors placed in

the kitchen, lounge, study, bedroom and bathroom. The external RH is measured using a

small external weather station. All this data has been collected and compiled by Leeds

Metropolitan University Researchers. Figure 33 shows the daily average RH for the

external environment and the RH for the specified Denby Dale areas.

69

Figure 33. Denby Dale daily average RH for internal and external environments

(Source: Leeds Metropolitan University)

0

20

40

60

80

100

120

Rel

ati

ve

Hu

mid

ity (

%)

Daily Average Relative Humidity

External

Kitchen

Lounge

Study

Bedroom

Bathroom

70

From 28/06/2011 to 21/9/2011 there has been a period of unmonitored data, due to full

data loggers. The purpose of analysing this data is to ascertain whether the dwelling has

performed within thermal comfort levels, and to identify the factors which affect RH.

At the start of the monitoring period, 20/07/2010 to 20/09/2010, internal RH ranged

from 60% to 75%. However soon after, the results show that the RH at between 35%

and 65% is better controlled and within a satisfactory range for health and thermal

comfort. A possible explanation for this improvement maybe due to the initial setup of

the MVHR system. The residents at have stated in the interview (Question 11) that it

has taken some time to fully adjust and optimise the MVHR settings to achieve

satisfactory comfort. It is likely that the MVHR system was providing low level of air

supply, which corroborate the observation that ‘the higher the fresh air rate, the lower

the indoor relative humidity’ (PHI, 2006, p.1).

Figure 33 shows a large observed difference between the external and internal RH. PHI

(2006) states that the MVHR system and the filters do not change the moisture content

of the external air whilst ventilated into the house, which removes the possibility that

the MVHR system could be ‘drying’ out the air. However absolute humidity in cold air

volume is much lower than that of heated air, for example 3g/m3 moisture at -5°C air

temperature is approximately 90% of humidity saturation (PHI, 2006). The same 3g/m3

of moisture at an air temperature of 20°C would only constitute to 17.6% of humidity

(ibid). Therefore as the external temperature of the air decreases so does its capacity to

hold water. The MVHR system then heats the cold air which causing the RH of the air

to drop, and resulting in low levels of RH within the house. The effect of this can be

seen in Figure 34.

71

Figure 34. Denby Dale external temperatures and internal humidity comparison

(Data source: Leeds Metropolitan University)

Figure 34 shows the close correlation of the external average temperature and the

internal humidity (lounge). Within this cold period, 05/12/2011 to 05/1/2012, the

temperature difference between external air and required internal air temperature is

between 9°C and 19°C. When the initial cold air is heated, the moisture content stays

the same, however the RH to heated air is reduced.

A simple linear regression shows the relationship between the independent (External

Temperature) and dependant (Lounge RH) variables. Figure 35 is produced from the

Denby Dale data extending from the annual period of 04/01/11 to 04/01/12, again with

the period of unmonitored data from 28/06/2011 to 21/9/2011.

The R2 value is 0.6752. This shows how much variation the relationship explains. The

nearer the R2

value is to 1 the better the ‘fit’. Wicks (1998) states that R2

values

exceeding 0.7 are regarded as high and generally means the model fits well.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

External Temperature and Internal Relative Humidity

Denby Dale

Average External Temperature (°C) Lounge Relative Humidity (%)

72

Figure 35. Relationship between lounge RH and external temperature

The value of 0.6752 slightly falls below this and when multiplied by 100, gives a

confidence level of 68%. It can be concluded that there is a relationship between

external temperature and internal RH within Denby Dale. However there are other

factors which affect the results which prevent 100% confidence levels. Other factors

which could affect the internal RH could include: the presence of plants, number of

people, and activities such as showers clothes drying.

As a result of periods of low humidity one of the residents suffered from a dry throat

during the winter period (Question 14). The lowest RH reading during this winter

period was 34% on 02/01/2011, this is most likely to be the approximate date when the

resident suffered from a dry throat. A RH figure of 34% is still deemed an acceptable

level according to ASHRAE (2001) cited in (Lstiburek, 2002), as the author states that a

dry nose, throat, eyes and skin normally occur when RH is around 25% at 20°C.

However this figure is not likely to apply with everyone, as Lstiburek (2002)

R² = 0.6752

0

10

20

30

40

50

60

70

80

-5 0 5 10 15 20 25

Lou

nge

RH

(%

)

External Temperature (°C)

Linear Regression:

External Temperature and Lounge RH

73

acknowledges that people have different levels of sensitivities. In the case Denby Dale,

the resident may have a higher level of sensitivity to low levels of humidity than the

average person.

A confidence level of 68% indicates a good model fit however other sources of RH in

the dwelling such as, plants and residents in close proximity to the Tiny Tag monitors

may have reduced the confidence level of this model. A further experiment could be

undertaken to remove the possibility of other RH sources (e.g. plants and residents)

which may have caused the confidence level to decrease. The Tiny Tag monitors could

be placed near to or within the supply ductwork would reduce the Tiny Tag monitors

from picking up unwanted RH sources. Therefore the Tiny Tag monitors would monitor

RH directly concerning the supply air and would likely produce a model of increased

confidence.

5.9 Subjective assessment of maintenance, operations and comfort by occupants

Interview questions relate to any barriers the occupants encountered during the design

and construction stage, and the solutions devised to overcome them. The following

analyses the questions answered by the Denby Dale occupants in section 2.0

appendices.

Design and planning

Question 1 asks what the boundaries and requirements were during the planning phase

in order to obtain planning permission. The occupants stated that the house required to

have a coarse Yorkshire stone exterior cladding, to ensure the house followed suit with

the local area. This would of course be a requirement for any type of house being built

within the area and the fact that the dwelling is of a Passivhaus standard does not create

a limitation.

74

The occupants were able to pursue sustainable practices during the construction phase

by ensuring all materials had been locally sourced. This reducing transportation CO2

emissions during the build.

Question 2 relates to the original requirements and preferable aspects which the

occupants had to compromise in order to meet the Passivhaus requirements. The

occupants admitted that they had an open mind during the design phase of the house

because they had prior understanding and researched the importance of the design phase

to meet Passivhaus standards.

One aspect the owners had to compromise on was the size of the windows to the north

elevation. This north facing facade receives provides no solar heat gain and in effect

creates an area for heat loss. GBS did make the windows larger than initially designed,

in order to meet the homeowners requirements, and to compensate introduced higher

quality Knauf insulation to reduce heat loss through the cavity wall.

Due to the fact that GBS were able to rectify the homeowners’ concerns with larger

north facing windows, the homeowners, have answered yes to Question 3, and feel that

the house emits enough light throughout the buildings. The owners further expressed

that the large glazing to the south-west corner filters light though the length of the

dwelling which compensates for the smaller windows to the north of the house.

Question 4 then quantifies their opinion with 9/10 satisfaction for transmittance of light

into the building.

The answer to the subsequent questions shows that Passivhaus does allow for some

flexibility within the design stage to accompany peoples preferences when concerning

window dimensions.

75

Air quality, MVHR use and ventilation habits

Question 11, refers to the ventilation used in the house whether all from the MVHR

system or part natural as well. There is a myth that windows cannot be opened with

Passivhaus dwelling because of the indoor climate being controlled with a ventilation

system. This however is not true. The Denby Dale residents state that they can open

windows whenever they feel the need to. CEPHEUS (2001) found that 18% of

occupants in Passivhaus dwellings open windows, whilst the remaining 82%

exclusively use ventilation systems to exchange spent air. It can be seen that natural

ventilation is mostly due to personal preference and the MVHR system still functions

properly nonetheless (ibid).

Questions 12, 13 and 14 relate to maintenance and operational aspects of the Paul

MVHR system. The system is left to run continuously and the only maintenance

required is changing the air filters every so often. The residents also stated that the

MVHR system was very easy to use. This is not dissimilar the results found in

CEPHEUS (2001) project which states that 94% of the occupants are satisfied or very

satisfied with their ventilation system.

The residents have stated that if there was one criticism of the MVHR system, it is that

during winter ventilated air can become dry as discussed in Research Findings 2. They

were however able to rectify the problem by placing wet towels on the hand rails and

despite this remain satisfied by the MVHR system.

MVHR systems heat the air to a maximum of 50°C, any higher would result in burning

smells from dust pyrolysis (IBO, 2008). The residents have recalled no burning smells

emanating from the MVHR system, indicating that the system is working correctly and

efficiently.

76

Thermal comfort

Thermal comfort is one of the main principles of the Passivhaus standard. Thermal

comfort is difficult to quantify and measure because personal opinion is a large

contributor. Question 16 addresses the thermal comfort within Denby Dale which the

residents thought to be excellent, creating a pleasant environment. The high levels of

airtightness within the building and a fairly even temperature throughout Denby Dale

would contribute to the pleasant environment experienced by the residents. The

residents rated their overall satisfaction to the thermal environment in Denby Dale

10/10 (Question 17). The CEPHEUS (2001) project also saw similar results with 94%

satisfied residents with the indoor climate throughout the year. Furthermore little or no

temperature stratification, compared to normal houses, was felt to be highly pleasant.

5.10 Summary

The CO2e emissions are not a direct requirement for Passivhaus but are still a

significant consideration. The dwelling achieved a 56% to 75% reduction (depending on

SAP or PHPP emission factors) compared to Part L1-2010 Building Regulations. The

introduction of PV panels has contributed to a large decrease in CO2e emissions.

Internal CO2 recordings have generally indicated acceptable levels within the dwelling,

with few explainable discrepancies. The overall annual average of 685ppm is at a level

where thermal comfort can be maintained, and indicates the MVHR system is

performing effectively.

The average internal temperature of 22°C is higher than would have been computed

within PHPP during the design phase. Initial high temperature readings at the beginning

of the year were due to ongoing MVHR adjustments. The residents have stated that they

77

achieved thermal comfort once fine tuning the MVHR system, and therefore acceptable

for Passivhaus standards.

Internal RH levels tend to drop during the winter periods and have caused some

discomfort to the residents. However the residents have been able to rectify low RH

levels by drying damp towels. On the whole RH levels have been maintained at

comfortable levels between 40-70%.

Table 19 summarises the Passivhaus standards against the analysed data throughout

Chapters 4 and 5. The dwellings ability to prevent heat loss is shown to be acceptable

by the Passivhaus standard, relating the structural component U-values, overall window

and doors U-values, thermal bridging and airtightness. This has enabled the dwelling to

perform within the two main Passivhaus specifications: specific primary energy demand

(15 kWh/(m²/a)) and specific space heating requirement (92kWh/(m²/a)) as shown in

Table 19.

Table 19. Comparison of Passivhaus standards and Denby Dale’s performance

Measure Passivhaus

standard

Denby Dale

performance

Requirement

achieved?

Insulation Walls U ≤ 0.15 W/m²K 0.11 W/m²K Yes

Insulation Roof U ≤ 0.15 W/m²K 0.08 W/m²K Yes

Insulation Floor U ≤ 0.15 W/m²K 0.15 W/m²K Yes

Window, Frames

and Doors U ≤ 0.80 W/m²K 0.75W/m²K Yes

Window Glazing U ≤ 0.6 W/m²K 0.55 W/m²K Yes

Thermal Bridges Ψ ≤ 0.01 W/mK 0.01W/mK Yes

Air Tightness 0.60 ach@50Pa 0.33 ach@50Pa Yes

Ventilation MVHR efficiency ≥75% 92% Yes

Space Heating ≤ 15 kWh/(m²/a) 15 kWh/(m²/a) Yes

Annual PE ≤ 120 kWh/(m²/a) 92 kWh/(m²/a) Yes

78

Chapter 6: Conclusions

Introduction

The UK Government has set legally binding targets which require 80% reductions in

GHG emissions by 2050. The residential sector accounted for approximately 30% of the

UK’s total CO2 emissions in 2012. Which explains why reducing energy consumption

within the domestic sector has been a main priority on the Government’s agenda. The

Code for Sustainable Homes is a step taken by Government to reduce energy

consumption in this largely energy inefficient sector.

Alternatively Germany have adapted a highly energy efficient pre-construction

calculation method of developing dwellings called ‘Passivhaus’. Post-construction

research (CEPHEUS, 2001) shows that energy savings of approximately 75% have been

achieved using Passivhaus concepts in Central European countries. This reduced energy

consumption in dwellings would contribute significantly to meet Government’s

emission reduction targets for the UK domestic sector.

The majority of Passivhaus certified dwellings within Central European countries are

built using construction methods traditional to the country or region, the majority of

these being; timber frame, concrete, and masonry with external cladding. However, in

the UK cavity wall structures are traditionally used (65% of the housing stock), which

builders have knowledge of and skills relating to this type of construction. Consequently

this creates a major barrier to the UK in adopting Passivhaus standards because there is

very little research as to whether the Passivhaus standard can be achieved using cavity

wall structure.

Denby Dale is the only Passivhaus certified dwelling, built using cavity wall

construction in the UK. It has been necessary to investigate the construction detailing

79

involved at Denby Dale to determine how Passivhaus certification has been achieved

using cavity wall construction. Further analysis of data concerning energy consumption

has been required to corroborate calculated specific energy demands with Passivhaus

standards. Therefore the aim of this dissertation has been to assess whether Passivhaus

standards can be met in the UK using traditional cavity wall construction.

Passivhaus requirements

Passivhaus certification is dictated by PHPP (2007) calculations at the design stage.

Passivhaus final specific requirements are as follows; space heating demand must not

exceed 15 kWh/(m2a) and PE demand must not exceed 120 kWh/(m

2a). Passivhaus also

requires airtightness to not exceed 0.6ach @50pa. These are the main fundamentals a

dwelling must achieve (using PHPP and blower door tests) to obtain certification. For a

dwelling to meet these final requirements then Passivhaus construction fundamentals

must be met which concern heat transfer coefficients and thermal bridging. To assess

whether Passivhaus standards can be met using traditional cavity wall construction it

has been necessary to determine the construction fundamentals and energy performance

of Denby Dale.

To assess the performance of Denby Dale secondary research was sourced mostly from

GBS concerning the construction designs and techniques. Primary research, obtained

from Leeds Met researchers, concerning energy usage (gas, electricity, electricity

generated and STHW) was analysed. Further analysis was undertaken on data

concerning internal CO2 levels, RH and temperatures, and external RH and

temperatures. This data was us to assess the indoor environment, in terms of thermal

comfort, and how external factors may affect the internal environment. The interview

conducted with the residents also allowed for a subjective assessment on which to base

occupant satisfaction levels.

80

Research Findings

Information presented in the summary Table 19, Chapter 6, shows that all the

construction fundamentals, MVHR efficiency and airtightness tests have met

Passivhaus requirements enabling certification. The specific energy usage for space

heating demand and PE demand have both achieved the Passivhaus standard for the

annual period. Furthermore the thermal comfort in the dwelling has been perceived by

the residents to be exceptional when the MVHR system has been optimised. From these

results it can be concluded that Passivhaus requirements can be met in the UK using

traditional cavity wall construction.

Passivhaus and UK Government targets

The UK domestic sector has been identified to be a main offender for large energy

consumptions and high levels of GHG emissions. It is necessary to conclude from the

results the potential benefits that can occur from adopting Passivhaus in the UK.

The results have shown that Denby Dale produced CO2e emissions of 11.0 – 19.3

kg/(m2a). The majority of the CO2e emission savings have been a result of 90%

decreased space heating demands compared to the UK dwelling stock. PV electricity

production has also decreased CO2e emissions by 13% for PHPP factors and 36% using

SAP factors. Overall the dwelling has achieved a 56-75% improvement on ADL1-2010

building regulations. Therefore, adopting the Passivhaus standard on a large scale would

significantly reduce the affects new dwellings have on the domestic sectors

CO2emissions.

Advantages of Passivhaus cavity wall structure in the UK

Using traditional cavity wall, where skills and knowledge as most commonly related to

in the UK, is likely to improve the success of adopting Passivhaus for a number of

81

reasons. Using a method most common to UK builders and constructors will enable the

concept to be scaled across the country and enable benefits of reduced energy

consumption and CO2 emissions to be magnified. The presence of skills relating to

cavity structures in the UK will provide a platform in which to produce high quality

workmanship and attention to detail required to achieve Passivhaus standards.

Furthermore the materials related to building cavity wall structures (e.g. brickwork and

aircrete blocks) are freely available in the UK and would aid in expanding the concept

across the country.

If the Passivhaus concept was to be undertaken, in the UK, using alternative

construction methods such as timber frame or masonry with external cladding, then the

skills and materials associated with these construction methods are not present in the

UK and would have to be imported. By using cavity wall structure enables UK builders

to create Passivhaus dwellings which would be more advantageous to the UK’s

economy rather than relying on importation. Furthermore importing skills and materials

will incur transportation GHG emissions contradicting the main principle of a low

energy/carbon emitting dwelling.

6.1 Implications and Recommendations

Even though Passivhaus is mostly likely to be successfully adopted in the UK using

cavity wall construction, there are still some issues which would need to be overcome.

The successful delivery of Denby Dale required numerous tool box talks, full

cooperation of the building team and scrupulous attention to detail. This is likely to

increase costs to any other construction company if it were to be replicated. A

recommendation would be to conduct an area of research which would determine

whether replication of the proven techniques used in Denby Dale would be feasible and

at a similar cost of £141,000 of that of Denby Dale.

82

Airtightness in the UK housing stock is generally poor compared to other developed

countries such as Canada, Sweden and Switzerland. It is more difficult to create airtight

barriers in cavity wall structures compared to solid masonry and timber frame and is

just one example of where improved workmanship will need to be addressed.

Tradesmen will require a greater understanding of the Passivhaus concept in order to

appreciate the importance of quality workmanship and the detailing identified in this

dissertation.

A further investigation could be undertaken to determine the level of familiarity to UK

builders of cavity wall Passivhaus dwellings. UK tradesmen and builders will inevitably

have to increase understanding of the concept and finely adjust their current skills.

Conducting an interview with Denby Dale builders would gather information as to

whether cavity wall Passivhaus dwellings are a viable proposition for UK contractors.

The interview would provide direct information as to how easily UK tradesmen can

transfer their skills to construct a Passivhaus dwelling. Furthermore it will allow for

some subjective assessment to investigate whether the building skills used at Denby

Dale are easily replicable. Comparisons can then be made to German builders and UK

builders based on attitude and quality of workmanship.

If the concept is to undergo expansion then the availability of Passivhaus accredited

products would need to be increased. Triple glazing windows, for instance are not

widely available in the UK as compared to central European countries. MVHR systems

are also fundamental in Passivhaus dwellings. The Denby Dale Paul MVHR system was

imported from the German supplier and could not be sourced nationally. Other

specialist products used at Denby Dale include Teplo Ties Pro and Clima tapes and

grommets. At a holistic level, if the UK has to import Passivhaus accredited products

then transportation emissions would have a large impact and offset the dwellings low

83

CO2e emissions. It would be ideal to have UK based manufacturers for accredited

Passivhaus products to reduce this effect, this however is unlikely to happen. If future

demands where to increase for Passivhaus products then it is likely that bulk

transportation would take place and reduce GHG emissions per unit to a more

acceptable level.

Heating systems designed for lower heating demands are not widely available in the

UK. In the Denby Dale case the 4.8 kW Vaillant boiler was the lowest output boiler that

could be sourced. It is inefficient to install larger boilers than required. If the UK is to

adopt the Passivhaus standard on a large scale it would be beneficial that boilers of

smaller outputs were readily available.

Homeowners will undoubtedly have priorities and personal preferences when

concerning all aspects of a dwelling’s design. The PHPP calculation may not allow

enough scope for change to satisfy some individuals. The compromise of larger north

facing windows at Denby Dale was offset by more expensive higher quality Knauf

insulation. Therefore PHPP has provided some scope for realistic/sensible priorities in

this case. However it is likely that not everyone will be satisfied with the restrictions to

design that PHPP creates. It is therefore necessary to accept that some people will have

to compromise their original plans/needs if the dwelling is to meet Passivhaus

standards.

Overall then, although Passivhaus may be able technically to be adapted to UK

housebuilding techniques, there are still a number of constraints that could affect its

widespread uptake in the UK despite the undoubted benefits that it has been shown to

offer.

84

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94

Appendices

Contents Page

1.0 Denby Dale photographs 95

2.0 Denby Dale interview questions and answers 98

3.0 Informed consent form 101

4.0 Denby Dale plans 102

95

1.0 Denby Dale photographs

Figure 36. Denby Dale south elevation

Figure 37. Denby Dale south-east elevation

96

Figure 38. Denby Dale north elevation

Figure 39. Denby Dale Vaillant gas boiler and STHW storage tank

97

Figure 40. Denby Dale MVHR system in garage

Figure 41. Denby Dale supply and extract ducts

98

2.0 Denby Dale interview questions and answers

Design and Planning

1. Do you know of any requirements that had to be met in order for the plans

to obtain planning permission? E.g., was the external cladding chosen by

owners or was it a requirement?

To obtain planning permission the house had to have a coarse Yorkshire stone exterior

cladding. This was to ensure the house followed suit with the local area. The occupants

initially wanted a rendered exterior, however this had been turned down due to planning

permission.

The majority of the materials had been sourced locally to ensure small transportation

carbon emissions. This was not a requirement to obtain planning permission, but a

concept which the owners chose to carry out.

2. Did you have to change any initial designs you may have liked for your

home in order to reach the Passivhaus standard or planning permissions?

For example, did the client want more windows, or larger windows, or a

greater quantity of windows the North facing side?

The owners accepted a relatively open mind when referring to the design of the house.

This was because they acknowledged the Passivhaus standard and had prior

understanding of the importance behind the house design in order to meet PassivHaus

requirements.

The owners had initially wanted under floor heating to be included within the plans,

however this was proved not to be necessary within a Passivhaus as the internal surface

temperatures of the floors are similar to that of the air temperature.

Some of the initial plans had included very small windows to the North Elevation of the

house. However the owners preferred to have these windows made larger to create a

better view of the back garden. The GBS had rectified this, however had to comprise by

using a higher quality Knauf insulation which would lower the U-values of the building

fabric and reduce the space heating requirements calculated in the PHPP package.

3. Does the window area on the North elevation provide sufficient light?

The owners answers Yes and feel bedrooms and bathroom to the north elevation do not

require much light. Furthermore the large glazing area to the S.W corner of the house,

allows light to permeate right through the house to the lounge area and top bedroom

with balcony.

4. Overall how well does the house allow natural light to pass in? out of 10?

9/10

5. Did the house receive a Code for sustainable homes rating? If yes what was

it?

99

3

6. Has the house received a Code for sustainable homes rating after the

installation of PV cells and solar water heating?

No

Energy Usage

Two towel rails are connected to the heating system, however with little function.

Therefore electrical elements installed to provide for drying of towels when required.

7. Do you use the heating elements in the towel rails? If so how often?

The owners have never used the towel rails as the MVHR system provides sufficient

drying.

8. What type of gas cooker do you have? And how often do you use the gas

cooker per week?

NEFF electrical oven and grill, NEFF gas cooker roughly used twice a day.

9. Has the occupants changed this set temperature over the past year?

Occupants have continually adjusted the temperature to their liking, to improve thermal

comfort.

10. When was the gas heater installed in the garage?

Just a small electric heater.

Ventilation

11. Does the Mechanical ventilation with heat recovery system provide

ventilation to your liking, or do you choose to open windows within the

house?

If yes do occupants open windows in winter or summer or both?

The owners open windows whenever they feel the need to.

There was some overheating in the winter because the system had not been fully

optimised, as the occupants were in the process of adjusting the boiler in order to find a

comfortable temperature threshold.

The owners also experienced some overheating in the summer due to hot external air

being drawn in through the MVHR. The passive solar gains created from large South

glazing, caused a lot of heat storage via thermal mass. This caused overheating at night

due to the release of stored heat from the thermal mass. The owners were able to rectify

this problem by using the external blinds to reduce passive solar gains during the day

and open windows at night to remove excess heat released from thermal mass.

12. Does the MVHR require constant adjustments or is it left to run?

100

The MVHR is left to run, but have the ability to boost the ventilation if required. The

system requires the filters to be changed every so often and is the only required

maintenance.

13. Is the MVHR user friendly, easy to use?

Very easy to use

14. Have there been any problems with the MVHR, such as:

- Unpleasant burning smells

- Humidity levels, air too humid or too dry?

No burning smells

Occupants are conscious of the fact that incoming warmed fresh air is dry and also

incoming external cold air that is heated is also dry. One occasion the occupant had a

dry throat on which they rectified by placing wet towels on the hand rails.

15. Does the MVHR remove excess heat effectively? created from sources such

as: cooking stove and towel rails.

The occupants have never known the MVHR’s ability to remove heat from the house as

they have always taken advantage using natural ventilation by opening the windows to

remove excess heat.

Thermal Comfort

One of the main principles of Passivhaus is to achieve thermal comfort for habitants.

Thermal comfort “the condition of mind which expresses satisfaction with the thermal

environment”.

16. How would you describe the thermal comfort of the house?

Pleasant environment, have the advantage of being able to adjust MVHR to achieve

high thermal comfort

17. Out of 10, what is the overall satisfaction with the thermal environment

within the house?

10/10. The occupants have stated that with living in a Passivhaus has made them a lot

more aware of their energy usage.

Also extremely satisfied with lower energy bills. Denby Dale annual energy bills

amount to approximately £300.

101

3.0 Informed Consent Form

Dear .........

I am studying for a Construction Management degree at Leeds Metropolitan University.

As part of my course, I am writing a dissertation on how PassivHaus can be best

applied to new builds within the UK (please see project information sheet for more

details).

My research so far has included the technicalities involved behind the design and

construction of Denby Dale, I have obtained the majority of information from the Green

Building Store. In order to improve my research I would like to ask permission to use

data monitored within Denby Dale collected by Leeds Met researchers. The data which

I would hope use within my dissertation would be the monitoring of temperature,

energy usage, CO2 levels and humidity. I hope to use this data to assess the

performance of the building in relation to the Passivhaus standard.

I would like to conduct an interview with you focusing on energy usage within Denby

Dale and your opinion on thermal comfort within the dwelling. The interview would take

approximately 30 minutes, during which I will take notes for accuracy.

My dissertation may be made available to other students and the general public in the

university library. I will ensure your anonymity by excluding identifiable personal data

from the dissertation. However, please be aware that one of your colleagues or any

other person who knows that you have taken part in the study may be able to

recognise your input from what is said. Your participation in this study is on a voluntary

basis and you are free to withdraw from the study if you inform me.

If you have any questions about my study, I will be glad to answer them. You can reach

me on my mobile phone on 07885564866 or by email:

M.Corran3247@student.leedsmet.ac.uk You can also contact my supervisor John

Bradley for further information by e-mail J.L.Bradley@leedsmet.ac.uk.

Please sign and date the statement below if you are willing to participate. Many thanks

for your interest in my research,

Yours sincerely,

Michael Corran

Consent agreement

I, , have read the above statement and understand its

contents. I have been given the opportunity to ask questions and discuss any

concerns. I agree to participate in the study as it has been explained. I understand that

extracts of the interview may be used, in anonymous form, in the student’s dissertation.

However I understand also that my identity will not be disclosed by the researcher or

the University.

Name . Date .

PLEASE RETURN SIGNED COPY TO THE STUDENT, AND RETAIN A COPY FOR

YOUR OWN RECORDS

102

4.0 Denby Dale plans

Figure 42. Denby Dale ground floor, plan (Source: GBS)

103

Figure 43. Denby Dale first floor, plan (Source: GBS)

104

Figure 44. Denby Dale north elevation (Source: GBS)

105

Figure 45. Denby Dale east elevation (Source: GBS)

106

Figure 46. Denby Dale south elevation (Source: GBS)

107

Figure 47. Denby Dale west elevation (Source: GBS)