Hong, S

Oreszczyn, T

Ridley, I

English

UCL Discovery

THE IMPACT OF ENERGY EFFICIENT REFURBISHMENT ON THE AIRTIGHTNESS IN ENGLISH DWELLINGS   Sung H. Hong1, Ian Ridley2, Tadj Oreszczyn3, The Warm Front Study Group4  1, 2, 3 Bartlett School of Graduate Studies, Faculty of the Built Environment,  University College London, London, WC1E 6BT, UK 4The Centre for Regional, Economic and Social Research, Sheffield Hallam University,  City Campus, Howard Street, Sheffield, S1 1WB, UK 4Environmental Epidemiology Unit, London School of Hygiene & Tropical Medicine Keppel Street, London WC1E 7HT 4National Centre for Social Research    ABSTRACT  A fan-pressurisation method was used to test the air infiltration rate of 191 dwellings in England.  All tested homes were either pre or post the introduction of energy efficient retrofit measures such as cavity wall insulation, loft insulation, draught stripping and energy efficient heating system.  Results show that the average air infiltration rate of the post dwellings is only marginally lower by 4% compared to the pre dwellings.   Component infiltration rate based on model prediction indicates the combination of cavity wall insulation, loft insulation and draught stripping potentially reducing infiltration rate by 24%.  However, longitudinal comparison shows a retrofit gas central heating system offsets this effect by contributing 13% increase in the infiltration rate.   KEYWORDS  air infiltration, refurbishment, insulation, draught stripping, central heating, English dwelling   INTRODUCTION     As a part of the UK government’s commitment to reduce green house gas emissions, measures to improve airtightness in the UK dwellings are being implemented through building regulation and energy efficient refurbishment programs.       Warm Front (WF) is a major energy efficient refurbishment project undertaken primarily to reduce fuel poverty in England by delivering affordable warmth through improved household energy efficiency.  The main elements comprising the WF energy efficiency package are cavity wall insulation (CWI), loft insulation (LI), draught stripping (DS) and depending on the householders’ qualification, the option of a hot water tank jacket and gas wall convector heaters or a gas central heating system (CH).       In 2001, the “Health Impact Evaluation of Warm Front” study was commissioned to investigate the effect of WF on resident health.  Household data from 3099 properties was collected over two successive winters in five urban areas: Birmingham, Liverpool, Manchester, Newcastle and Southampton. A subset of 191 properties was targeted to conduct 221 (78 pre-intervention and 143 post-intervention) air infiltration rate tests.  The case study dwellings are classified as pre- or post-intervention depending on the completion status of the WF refurbishment work.        This paper will present the results of the field-measured, whole house, air infiltration rate tests and discuss the effect of different energy efficient refurbishment measures on the dwelling infiltration rate.  The parameter used to present the infiltration rate is air permeability which is used by the UK building regulations and expressed in units of m3/hr/m2 (of exposed building envelope area including the ground floor) at 50 Pascals [2000, CIBSE].     OPPORTUNITIES FOR ACHIEVING AIRTIGHTNESS     Results from past projects indicate that refurbishment work offer a great opportunity to achieve airtightness in UK dwellings.  Studies carried out by Leeds Metropolitan University on a group of 12 properties (Derwentside Project) have shown a 46 to 66% reduction in the infiltration rate [1997, BRESCU] while a maximum of 71% reduction was observed in a single case study dwelling following refurbishment measures (York Project) [Lowe, et al., 1997].  WF, on the other hand, is expected to have a lesser impact in reducing the infiltration rate as a result of fewer delivered airtightness measures as shown in table 1.    TABLE 1 Opportunities of achieving airtightness  Opportunities of Achieving Airtightness  WF  York  Derwentside Draughtstrip loft hatch and fit securing bolts  X  X  X Draughtstrip opening windows and external doors  X  X  X Seal around windows and door frames      X Seal service holes through timber floors    X   Seal service penetrations through ceilings       Seal all remaining plumbing services       Seal all joints in heating ductwork (where possible)      X Seal all electric services including faceplates      X Hardboard across timber floors and seal to skirting    X   Install cavity wall and loft insulation  X  X  X Seal air space behind plasterboard dry-lining    X  X Seal top and bottom of stud partitions       Add a draught lobby to exterior doors       Block disused chimney opening         MEASURING THE AIR INFILTRATION RATE     A fan pressurisation method was used to measure the whole house air infiltration rate.  All open flues and vents were kept open during the test in order to measure airtightness under a normal dwelling condition.  Open chimneys were sealed but depending on the circumstance they were left open and only the pressurisation cycle was carried out.  The test was accompanied by a thermal imaging camera to record areas of air ingress and missing insulation.   The tested dwellings are classified in table 2 which shows that the majority are of masonry construction.    TABLE 2 Case study dwellings (n=191)  age wall  type  building  type pre-1900 15%  cavity  masonry  66%  terraced 57% 1900 – 1950  50%  solid brick  33%  semi-detached  33% 1951 – 1976  32%  timber framed  0.5%  flats  9% Post 1976  3%  other  0.5%  detached  1% PRE- AND POST-INTERVENTION AIR INFILTRATION RATE     The comparison of air infiltration rate distribution between the pre- and post-intervention dwellings in figure 1 shows little difference between the two groups with the post- dwellings showing a marginally lower average infiltration rate of 0.7m3/hr/m2 in table 3.  One of the main reasons seems to be the fact that the impact of measures which may result in decreased infiltration rate such as the CWI and DS is offset by other measures such as the installation of a CH whose effect is shown by the increase in infiltration rate among the CH properties in table 3.  051015-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44air permeability (m3/hr/m2 @ 50 Pascals)number of casesPost-intervention (n=143)Pre-intervention (n=78)Normal distribution (Post)Normal distribution (Pre)  Figure 1: Air infiltration rate distribution for pre- and post-intervention WF dwellings  TABLE 3  Mean and standard deviation of air infiltration rates (n=221)  WF Scheme  Pre-WF (m3/hr/m2) Post-WF  (m3/hr/m2)  % Change All properties  17.7 (s.d. 7.1), n = 78  17.0 (s.d. 7.2), n = 143  -4% w/o CH  19.1 (s.d. 7.8), n = 22  16.5 (s.d. 7.3), n = 51  -14%  w/ CH  17.1 (s.d. 6.8), n = 56  17.2 (s.d. 7.2), n = 92  +1%     CH: Gas Central Heating System  TABLE 4 Change in air infiltration rate based on longitudinal cases (n=21)    Intervention Sample  Size Infiltration Rate Change (m3/hr/m2) % Change w/ PU  4  + 3.0   +21%  CH only w/ PA 12 8 +1.8 + 1.1  +13% +9% CH w/ PU + LI + DS   2  +2.1  +10% CH w/ PU +PA + DG  2  -0.3  -3% CH w/ PA + CWI  2  -3.5  -27% CWI 1  -3.6  -19% New Boiler  2  +0.2  +2% CH w/ PU: gas central heating system with plumbing installed under floor boards  CH w/ PA: gas central heating system with plumbing installed above floor boards  LI:  loft insulation; DS: draught stripping; DG: double glazing; CWI: cavity wall insulation     Longitudinal test results from a subset of 21 properties further supports the observation where a decrease in the infiltration rate is recorded following the CWI and double glazing - not a WF measure - while an increase of 13% is observed following the CH measure alone.  This increase is not the result of an additional flue since the flues are of balanced type but from the plumbing work associated with the WF supplied radiators.  Table 4 shows a pronounced increase in the infiltration rate by 21% among the dwellings whose radiator pipes are installed below the suspended floor boards at ground floor level.   COMPONENT INFILTRATION RATE     Because of the small sample size involved in the longitudinal study and most of them having received only a CH, a statistical model based on multiple regression is used to estimate the effect of component contribution to the infiltration rate based on the 221 measured samples.  The model shows that 31% (R2=0.314) of variability in the infiltration rate is explainable by the components listed in figure 2 (P-value = 4.9 x 10-12).  The components that most significantly affect the infiltration rate (P-value < 0.05) are indicated as grey bars.  m=0.4 m=0.7m=4.1m=0.3m=1.6m=0.8m=4.2m=5.1m=9.4m=3.4m=2.2m=3.3 m=3.3p>0.05p>0.05p<0.05p<0.05p<0.05p<0.05p<0.05p<0.001p<0.05p<0.01p>0.05p<0.001p=0.105101520othersides shelteredsolid wall (%)cavity wall unfilled (%)single masonry (%)suspended floor unsealed (%)loft uninsulated (%)window loose (%)window non-draught stripped (%)radiator, single open chimney, single open flue, single vent or fan, singleair permeability (m3/hr/m2 @ 50 Pa) Figure 2: Component infiltration rate at 95% confidence interval range (m: median; p: P-value)     The model indicates that a combination of CWI, LI and DS, which are the primary WF airtightness measures, should achieve a 24% reduction in the infiltration rate based on the range median.  The reduction will increase to 37% if the suspended floors are sealed and a further 47% if an unwanted chimney is closed.  The timber cladding component refers to the construction of exterior timber boards on wooden battens with internal plasterboard finish or internal single skin brick finish.  The large effective range of this component indicates the need for a further classification into the two internal wall types.  The model shows that the potential impact of this wall type on the infiltration rate can be significant while its construction nature does not allow retrofit CWI.       Increase in the dwelling sides sheltered increases air permeability by 3m3/hr/m2.  In other words, a unit wall of a semi-detached house is leakier than a detached house.  The reason behind this oddity is due to the way in which the air permeability parameter is based on exposed wall surface area while discounting the effects of inter-dwelling air exchange.  Building Research Establishment (BRE) study shows inter-dwelling infiltration through walls can contribute from zero to 20% of total infiltration rate [1998, Stephen].      LI can reduce air permeability by 4m3/hr/m2.  However, post-intervention survey as in figure 3 shows that this potential benefit is frequently lost as a result of the missing LI along the ceiling edges near the eaves where retrofit installation is physically difficult to carry out.  Without the LI over the wall plate, air can travel up the cavity wall space if the CWI and closers are missing or behind the drywall finish with poorly sealed surrounds.       8.7°C16.4°C910111213141516AR01SP01LI01  Figure 3: Thermographic image shows missing loft insulation behind the ceiling finish near the eaves     A single retrofit radiator increases air permeability by 0.3m3/hr/m2.  If the effect of the WF supplied radiators - normally five - is taken into account, the potential increase from a CH can be 1.5m3/hr/m2 which is similar to the increase of 1.8m3/hr/m2 observed in the longitudinal comparison of table 4.       Minute cracks, unsealed penetrations and other paths that are difficult to classify make up the other component which contributes 3m3/hr/m2 to the infiltration rate.  WF measures may have limited effect in reducing this component which possibly reflects the general construction quality of the dwelling and its deterioration through age.  A more detailed component classification may reduce the effect of the other component while increasing the significance level (R2 value) of the prediction model.        Poor component classification can be attributed to the low significance level (P-value >= 0.05) of the open flue, single & vent or fan, single components.  No detailed survey was made between the flues of open gas fire and those of modern gas fires with grilled front.  Similarly, the condition of permanent vents such as air bricks was not surveyed in detail.       COMPARISON OF THE COMPONENT INFILTRATION RATES     The model prediction is compared in figure 4 with BRE’s component infiltration rate which is based on reductive sealing method from 35 UK dwellings [1998, Stephen].  For the comparison, the effect of the WF CWI is related to the BRE drywall surrounds sealing because no record was made about the type of internal wall finish in the WF study.   The loft hatch component is omitted in the WF model because of its poor significance level.  The contribution from open chimneys and flues are all omitted because the BRE data excludes their effects.  Also, the CH contribution is excluded since its effect on infiltration rate is significant only as a retrofit measure, a condition unique to the WF project.       The comparison of the component infiltration rate between the WF and the BRE data is not straight forward due to the difference in component classification.  In the case of the permanent vents, the model is predicting the effect from a single vent or fan (1%) whereas the BRE prediction is based on several vents (9%) typically found in the English dwellings.  The large difference between the CWI (11%) and the BRE dry wall surrounds sealing (2%) and likewise between loft uninsulated (14%) and the BRE loft hatch (2%) indicates that their effects can’t be directly compared.  BRE’s remainder component which makes up 71% of the total infiltration rate can be equated to the model’s solid wall (7%), single masonry (31%), suspended floor (17%) and other (11%) components which in combination contribute to 66% of the total.  The model predicted effect from no draught stripping and window & door loose make up 8% which is less than the BRE’s 16% possibly because the model does not take into account the contribution from well sealed and draught stripped windows and doors.              cavity wall unfilled(11%)solid wall(7%)other(11%)window & door loose (3%)vent or fan, single(1%)suspended floor unsealed(17%) no draughtstripping(5%)single masonry wall(31%)loft uninsulated(14%)  surrounds(2%)loft hatch (2%)permanent vents(9%)windows & doors (16%)remainder, (71%)  Figure 4: Comparison of the component infiltration rate   CONCLUSION     The combination of Warm Front delivered cavity wall insulation, loft insulation and draught stripping can reduce the English dwelling air infiltration rate by about 24%.  On the other hand, retrofit gas central heating system increases the infiltration rate, which is particularly sensitive to the way in which the peripheral piping work is installed.  To achieve airtightness, the radiator pipes should be installed exposed above the suspended floor, or if installed below the floor, they should be accompanied by a robust sealing procedure around the penetrations and along the seams of floorboards temporarily lifted for installation.     ACKNOWLEDGEMENTS     This study was funded by a grant from the Department for Environment, Food and Rural Affairs (Defra) and the Welsh Assembly Government.  We are grateful to Energy Saving Trust under whose contract the services were carried out and to EAGA Partnership for their support.  We are also grateful to the householders for their warm welcome into their homes.      REFERENCE  Lowe, R. J., Johnston, D. and Bell, M. (1997). Airtighntess in UK Dwellings: A Review of Some Recent Measurements.  In Proc. Second International Conference on Building and the Environment, June 1997, Paris, 389-396.  Stephen, R. K. (1998). Airtightness in UK dwellings: BRE’s test results and their significance, Building Research Establishment, Garston, U.K.  (2002). Conservation of fuel and power in dwellings, Building Regulations Approved Document L1, The Stationery Office, London, U.K.  (1997). Improving airtightness in existing homes, Good Practice Guide 224, BRECSU, Building Research Establishment, Garston, U.K.  (2000). Testing buildings for air leakage, CIBSE TM23: 2000, The Chartered Institution of Building Services Engineers, London, U.K. WF Model  BRE [Stephen, 1998] 

Airtighntess in UK Dwellings: A Review of Some Recent Measurements. In

Conservation of fuel and power in dwellings, Building Regulations Approved Document L1, The Stationery Office,

Improving airtightness in existing homes, Good Practice Guide 224, BRECSU, Building Research Establishment,

Testing buildings for air leakage, CIBSE TM23: 2000, The Chartered Institution of Building Services Engineers,

The impact of energy efficient refurbishment on the airtightness in English dwellings

The impact of energy efficient refurbishment on the airtightness in English dwellings

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