Air tightness

Air leakage is a major cause of energy loss and home energy is responsible for almost 30% of CO2  emissions. Improving air tightness is the means of reducing air leakage - the uncontrolled flow of air (into and out of a building)through gaps and cracks. Part L of the Building Regulations require that pressure testing is carried out on new buildings or refurbished buildings and the results passed to the Local Authority, but measures to improve existing dwellings and commercial buildings are matters for owners and occupiers.

Air leakage is measured as the rate of leakage in cubic metres per hour for each square metre of a building with a given air pressure inside the building. The Building Regulations set this at 10m3/h/m2 @50 Pa. Good practice would be indicated by a rate of 7m3/h/m2, but even very few new buildings achieve this. Air leakage in existing buildings is much more difficult to control and it is usually a matter of trying to reduce air leakage to improve comfort by filling gaps. Suspended timber ground floors, where there is a ventilated space beneath can usually be improved by laying hardboard or plywood over the boards and sealing gaps at skirtings. There are also often gaps under baths and around pipes. Window frames and cills and external door frames are often a sources of leakage.
See also ventilation