Blue Tree Acoustics Frequently Asked Questions (FAQ) #14
Which building types need to be Air Tightness tested?
New build dwellings; all new buildings other than dwellings and large extensions to buildings other than dwellings.
In some cases it is possible to assume a very poor level of performance in the SAP/SBEM calculation and then testing is not required.
For dwellings it is Approved Document L1A - Conservation of Fuel & Power (for England & Wales) that requires air tightness performance for new houses and flats. It does not require refurbishments, conversions or extensions to existing residential buildings to be air tested.
Small developments of a couple of houses may avoid the need to test by accepting an assumed poor value for air permeability of 15 m3/(h.m2) @ 50Pa. This is usually the wrong path to follow as to offset this in the SAP or SBEM calculation other areas of the building will have to be upgraded.
In a few situations, it may be possible to re-use existing test evidence where building designs have been repeated within 12 months of conducting the original test.
For buildings other than dwellings it is Approved Document L2A - Conservation of Fuel & Power (for England & Wales) that requires air tightness performance for new buildings other than dwellings. This applies to all heated buildings and includes industrial units, warehouses, hospitals, schools, universities, residential care homes, hotels, hostels, offices, retail units, and so on.
In a similar way to dwellings, small commercial buildings with a floor area less than 500m2 may avoid the need to test by accepting an assumed poor value for air permeability (15m3/(h.m2) @ 50Pa. Again this will add more cost than it saves, by requiring upgraded insulation etc to offset the poor air tightness in order that the building meets overall targets for emissions.
Large extensions to buildings other than dwellings are required by Approved Document L2B - Conservation of Fuel & Power (for England & Wales) to achieve a level of air tightness.
Large is defined as an extension greater than 100m2 AND greater than 25% of the useful floor area of the existing building.
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