Legislation/Technical Updates
Airtightness testing for new dwellings
It is almost six months since the publication of Part L1A Building Regulations, which includes airtightness testing as a requirement for new dwellings, and we can now begin to understand its effect on construction. Initial feedback from many house builders had suggested that the airtightness requirement would mean significant changes to construction methods. It was also felt that compliance with design air permeability targets would be onerous and add a considerable cost to the build price of a dwelling. With six months experience, is this true?
Quite simply, no.
Over the last year, BSRIA Airtightness has undertaken in excess of 300 tests for house builders. The testing has been performed for all types of house builder from single self builds through to the largest house building companies which deliver in excess of 10,000 units a year. Testing has been performed on all types of construction; timber frame, steel frame and traditional construction. The results show that in 83% of cases, house builders are already achieving compliance with the air permeability limit, 10m3/(hr.m2), and a further 11% are close, within 2m3/(hr.m2) of achieving this.
The testing results also show that some forms of construction are inherently easier to air seal. As one would expect, timber frame construction is proving to be the most successful in providing low air permeability results (98% compliance for houses and 100% for apartments). Traditional construction results can be broken down further by wet plaster (93%) and dry-lined (77%).
Results also show that for developments or phases of developments of 30 homes or less, compliance was 92% against the overall average 83%. This suggests that the key to achieving compliance is consistent quality of construction, through closer supervision, as opposed to design detail. For example, many of the properties tested had areas where there was not a continuous seal along the dry-lining and insufficient sealing on boiler flue penetrations.
There are some common instances where a lack of detail is to blame for failure: for example, no seal at joist level where the joist runs through to a vented area - particularly prevalent in 2.5 storey dwellings.
Where house builders are unsure of how effective their air sealing detail is, they can forward designs to be reviewed by airtightness testing companies.
BSRIA΄s discussions with building control and house builders have shown that actually passing the test is not the only concern. There is also the issue of test cost and availability of testing companies, as well as understanding how many and which dwellings will require testing.
At first, airtightness testing costs were envisaged to be on a par with sound testing for Part E. Even figures of £600 per test being suggested, however, some testing companies are offering airtightness testing from under £100 per dwelling on a national basis.
It was also thought that the sheer number of dwellings that required testing would mean that there would not be enough qualified testers to undertake the testing and they would not be available when the Site Agent needed them. Again, this has not proved to be the case. Calculations show that the total number of testing engineers required to undertake all the tests needed is approximately 60. There are enough companies already active in the market and registered for competence - or who have applied for registration through ATTMA (Air Tightness Testing and Measurement Association) - to meet this need. This should mean that getting a test performed should not be an issue. Some testing companies are offering a guaranteed national 72 hr response time to ensure handover is not affected.
Deciphering which and how many dwellings require testing can take some time to calculate, but again this is an issue with which house builders need not concern themselves. It is part of the service provided by reputable airtightness testing companies. They will calculate which and how many dwellings you are likely to need to test, whether you have opted to prove compliance by either accredited construction details or pre-completion testing.
www.bsria.co.uk/press/?press=354
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It is almost six months since the publication of Part L1A Building Regulations, which includes airtightness testing as a requirement for new dwellings, and we can now begin to understand its effect on construction. Initial feedback from many house builders had suggested that the airtightness requirement would mean significant changes to construction methods. It was also felt that compliance with design air permeability targets would be onerous and add a considerable cost to the build price of a dwelling. With six months experience, is this true?
Quite simply, no.
Over the last year, BSRIA Airtightness has undertaken in excess of 300 tests for house builders. The testing has been performed for all types of house builder from single self builds through to the largest house building companies which deliver in excess of 10,000 units a year. Testing has been performed on all types of construction; timber frame, steel frame and traditional construction. The results show that in 83% of cases, house builders are already achieving compliance with the air permeability limit, 10m3/(hr.m2), and a further 11% are close, within 2m3/(hr.m2) of achieving this.
The testing results also show that some forms of construction are inherently easier to air seal. As one would expect, timber frame construction is proving to be the most successful in providing low air permeability results (98% compliance for houses and 100% for apartments). Traditional construction results can be broken down further by wet plaster (93%) and dry-lined (77%).
Results also show that for developments or phases of developments of 30 homes or less, compliance was 92% against the overall average 83%. This suggests that the key to achieving compliance is consistent quality of construction, through closer supervision, as opposed to design detail. For example, many of the properties tested had areas where there was not a continuous seal along the dry-lining and insufficient sealing on boiler flue penetrations.
There are some common instances where a lack of detail is to blame for failure: for example, no seal at joist level where the joist runs through to a vented area - particularly prevalent in 2.5 storey dwellings.
Where house builders are unsure of how effective their air sealing detail is, they can forward designs to be reviewed by airtightness testing companies.
BSRIA΄s discussions with building control and house builders have shown that actually passing the test is not the only concern. There is also the issue of test cost and availability of testing companies, as well as understanding how many and which dwellings will require testing.
At first, airtightness testing costs were envisaged to be on a par with sound testing for Part E. Even figures of £600 per test being suggested, however, some testing companies are offering airtightness testing from under £100 per dwelling on a national basis.
It was also thought that the sheer number of dwellings that required testing would mean that there would not be enough qualified testers to undertake the testing and they would not be available when the Site Agent needed them. Again, this has not proved to be the case. Calculations show that the total number of testing engineers required to undertake all the tests needed is approximately 60. There are enough companies already active in the market and registered for competence - or who have applied for registration through ATTMA (Air Tightness Testing and Measurement Association) - to meet this need. This should mean that getting a test performed should not be an issue. Some testing companies are offering a guaranteed national 72 hr response time to ensure handover is not affected.
Deciphering which and how many dwellings require testing can take some time to calculate, but again this is an issue with which house builders need not concern themselves. It is part of the service provided by reputable airtightness testing companies. They will calculate which and how many dwellings you are likely to need to test, whether you have opted to prove compliance by either accredited construction details or pre-completion testing.
www.bsria.co.uk/press/?press=354
« Back
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