Frequently Asked Questions

Air leakage testing is considered by some as another government interference, another regulation that costs the builder time and money. In fact proving the air tightness of your properties can actually increase your net profitability for two reasons:

1st - By adhering to best building practices and entering a lower permeability rate in the SAP calculations, there will be less need for over-compensation with expensive thermal materials, meaning that you will reduce the overall building cost.

2nd - If by means of an air tightness test certificate you can demonstrate that your building has achieved the best possible air tightness rating, customers will usually tend to pay more for a house that costs less to heat. Air tightness testing is perhaps the most practical example of a quality build.

Q: What is building air leakage?

A: Air leakage is the uncontrolled flow of air through gaps and crack in the fabric of the building, not to be confused with ventilation, which is the controlled flow of air into and out of the building through purpose built ventilators.

Q: What is the detail behind the new regulations relating to Air Tightness Testing for domestic properties?

A: Gaps and cracks in the building fabric are often difficult to detect simply by visual inspections. Air leakage paths through the building fabric can be torturous; internal building finishes or external cladding often obscure gaps. The Approved Document L1 A 2006 requires that all new dwellings have an acceptable CO² emissions rate referred to as the Dwelling Emission Rate or DER. Part of the calculation procedure required to determine the DER refers to the actual leakage of air from the building. The lowest acceptable standard under building regulations is 10m³/(h.m²)@ 50 Pascals. Building control bodies only accept certificates from BINDT registered airtightness testers as evidence that the procedure has been followed.

Q: Why do we have test for airtightness in domestic properties?

A: Because proving the airtightness of a building is now part of the building regulation process. Domestic energy accounts for more than 25% of the U.K’s CO² emissions and Government currently aims to reduce CO² emissions by 20%-28% by 2010.

Q: I have a small development of 4 similar properties, how many of these do I need to have tested?

A: One

The guidelines state the following number of tests per dwelling type are required:

4 or less of the same style : 1
5 to 40 dwellings : 2
More than 40 dwellings : At least 5% unless the first five units/dwellings meet the prescribed standard then the sample size can be reduced to 2%

Q: Are there any exceptions?

A: Yes, several a single dwelling is exempt if the same style has been constructed in the proceeding 12 months by the same builder and can be shown to have achieved the prescribed standards of air tightness. Although note, the building control officer will decide which and how many units are actually tested. The need for Air Tightness Testing can also be avoided (for a development of no more than 2 dwellings) by using the default value of 15m/³/ (h.m/²) for the air permeability at 50Pa when calculating the DER in the SAP calculations. This will necessitate the use of improved standards of insulation or higher efficiency equipment with associate additional costs.

Q: Do extensions need to be tested?

A: Where an extension is proposed to an existing building with a total useful floor area over 1000 sq.m. the building is to be upgraded, insofar as it is technically, functionally and economically feasible to meet the requirements of Part L. (This is to meet the requirements of Article 6 of the Energy Performance of Buildings Directive). For average dwellings, therefore, pressure testing of extensions is unlikely to be required. BUT watch this space, as it could be a key area for the Government to use in reducing CO² emissions.

Q: When should Air Tightness Test take place?

A: Air tightness testing should be conducted during the latter stages of construction of the first 25% of each new dwelling type. There are clear benefits to the principle contractor that the airtightness of a development is assessed at the earliest opportunity to ensure there is compliance with best practice.

Q How much does Air Tightness Test cost?

A: It depends on the size and complexity of the property, the location and the level of preparedness of the building. The cheapest quote is not always the best as re-tests can be expensive. It’s useful to consider several U.K studies have shown that improved and demonstrable property airtightness can yield energy savings of 15% to 30%. This should result in a higher sale price for the property because of on going reduced energy costs.

Q: How long does typical domestic Air Tightness Test take?

A: It depends on the size of the property, how many apertures need to be taped over and if you are able to provided a full set of plans (preferably in an electronic format) But the duration of the actual test should take no longer than two hours. If the property passed the Airtightness test a certificate will normally be available within 7 days of the test being completed.

Q: What happens if an Air Tightness Test fails?

A: Should a dwelling fail to meet the required standards of air permeability, then the weakness should be identified (there are a number of particularly common areas) Remedial work should be carried out. The regulations state that for each dwelling which fails the air tests on an accredited build, a re-test of the failed build plus an additional dwelling of that design should also be tested. For non-accredited builds, a re-test of the building plus two additional dwellings of the same type must also be tested. (Accredited Construction Details are available for free download from the Communities and Local Government website) - www.communities.gov.uk

Q: So how do you actually measure Air leakage?

The pressure differential is measured across the envelope of the building by means of a large fan installed temporally, usually in a doorway. All relevant openings into the property are temporally sealed and a range of static pressures and environmental readings are taken. The fan is switched on and the air pressure in the property is gradually increased or decreased and the differential pressure is recorded at each step. Employees can continue work within the property but all windows and doors have to remain closed for the duration of the test. The total air flow required to achieve a pressure differential of 50 Pa is calculated and divided by the total building envelope area to provide the leakage rate in m³/h.m²)@50Pa.