Blue Tree Acoustics Frequently Asked Questions (FAQ) #15


Is every building Air Tightness tested?


For non-dwellings yes. All new build building including industrial units, warehouses, hospitals, schools, universities, residential care homes, hotels, hostels, offices, retail units, and so on. For buildings other than dwellings each individual building unit will need to be tested.

For dwellings, No

For dwellings a sampling rate applies depending on the dwelling type and whether or not the Accredited Construction Details have been used.

The number of tests required varies depending on the size of the development and the number of dwelling types e.g. flats, terraced houses, semi-detached, detached etc. Small sites may require only one test. Larger sites may require many more tests.

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

Dwelling types are: Detached; Semi-detached; Top floor flat; Mid floor flat; Ground floor flat; End terrace; Mid Terrace.

Also there should be subdivision in types so that there is a difference of no more than 15% in gross floor area between the smallest to largest in the group.

There should also be no more than 1 extra significant opening in the group.

Typically, a site will require between 2 and 10 tests.

Separate blocks of flats are considered as different developments.

Accredited Construction Details

Part L1A refers to Accredited Construction Details (ACD), these can be found on the Planning Portal website.

The details refer to insulation as well as air permeability and are divided into the following construction types: Timber frame; Steel frame; Masonry (cavity insulation); Masonry (internal insulation); Masonry (external insulation).

They include details for various elements of the dwelling, including: Ground floor to wall; Wall to ceiling; Party walls and floors to external walls; Eaves; Windows; Doors.

Adoption of these details will need to be verified by Building Control or the Approved Inspector.

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