Air Tightness (or air permeability) relates to the loss of air from inside a building to the outside and the air coming from outside to inside. This is often felt to us as draughts through cracks and poorly sealed joints. Good air tightness is vital in an energy efficient build, as in some buildings with poor air tightness it can result in up to 40% of heat loss from buildings.

Technical information

Air tightness is very important for the energy efficiency of the building. The benefits of improved insulation and more energy efficient heating systems are lost if warm air can leak out of the building and cold air can leak in.

As the Government strives to reduce CO2 emissions from new buildings, the Building Regulations now place greater emphasis on the quality of the fabric of the building.

Increased insulation and the continuity of insulation combined with reductions in air leakage significantly reduce the heat losses from a building and the CO2 emissions.

Consequently the need for the test is now a Building Regulations requirement under Approved Document L1A and the result is used in the energy assessment (SAP) of the building which is the tool used to demonstrate compliance.

Air Tightness Testing is a requirement for all new builds. The test involves sealing of all trickle vents and sources of designed ventilation, before using a large door mounted fan to de-pressurise the building. The rate that the air escapes is then measured and a rating is determined taking into account the size and volume of the building against a benchmark.

In order to pass the following needs to be achieved: • Building Regulation ADL1a: 10m3/(h/m²) at 50Pa • Best Practice: 4m3/(h/m²) at 50Pa • SAP Standard: 6m3/(h/m²) at 50Pa

Hints & Tips

There are ways to reduce the amount of air leakage in a dwelling by:

Sealing gaps and cracks

Using joist seals

Using Pro Clima Solitex Plus in roofs

Allow wires to pass through a Pro Clima Roflex

If a dwelling isn’t tested for air leakage then the default should be added which is 15m3/h/m2 @ 50Pa.

For a dwelling which isn’t tested but the same house type has, a margin of +2m3/h/m2 @ 50Pa should be added.