Building Regs Air Tightness

Air tightness – Building Regulations

The Building Regulations approved document Part L1A 2010 now specify that any new dwellings are built airtight. The regulation is focused upon conservation of fuel and power usage. Part L1A states that any new dwellings are tested for air tightness in accordance with Table 1 as shown below.

The Scottish Building Regulations, Section 6, states the requirement to build an airtight building and all new build domestic dwellings should be should be tested for air tightness (see Table 2 below).

Air tightness testing is carried out by using a method known as a ‘blower door test’ in accordance with BS EN 13829. The measurement is taken by blowing air into the house via a particular door that is mounted in the main entrance. By the use of thermographic equipment, leakage paths can be identified.

The new Part L1A requires an air tightness of maximum 10 m3/hr/m2 air loss at a pressure of 50 Pa. Standard good practice for air tightness testing in the UK is a maximum of 7 m3/hr/m2 and best practice is 3 m3/hr/m2 of air loss. Section 6 of The Scottish Building Regulation requires a maximum of 7 m3/hr/m2 of air loss at a pressure of 50 Pa. The Scottish regulations will be fully enforced for all dwellings by 1st October 2011 and this test is mandatory.

Number of pressure tests for dwellings that have not adopted accredited construction details


Table 1: Part L1A Regulations

Number of instances of the dwelling type Number of tests to be carried out on the dwelling type
4 or less: Two tests of each dwelling type.
Greater than 4, but equal to or less than 40: Three tests of each dwelling type.
More than 40: At least 10% of the dwelling type, unless the first 5 units of the type that are tested achieve the desired air permeability, when the sampling frequency can be subsequently reduced by 2%.


Table 2: Scottish Building Regulations 

Pressure test frequency Dwelling Description
Baseline: Testing of completed dwellings to be carried out on 1 in 20 dwellings or part thereof.
Large developments: It is advisable to test more than one example of the same dwelling type, completed at different stages in the overall development, to help establish consistency in quality of construction.
Smaller developments: The proportion of dwellings tested may need to increase, dependant on the range or type and form of dwellings present, to ensure a representative sample is taken.
One single dwelling: Air tightness testing should be carried out as it will not be possible to obtain comparative data on the quality of construction from similar dwellings. Alternatively, where a default design value of 15 m3/hr/m2 at 50 Pa is stated in demonstrating compliance under standard 6.1, testing need not be carried out.


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