Alternative Guidance for High Air Permeability Dwellings

In addition to this guidance, for each system, alternative guidance is provided for dwellings with as-built air permeabilities greater than 3 m3/(h.m2) at 50 Pa. It is recommended that this option is only selected if designing to an air permeability greater than 5 m3/(h.m2) at 50 Pa (e.g. such as 15 m3/(h.m2) at 50 Pa, allowed by Part F to avoid air pressure testing) and where the person carrying out the building work does not have previous experience of closely matching design with as-built air permeability levels. Where the alternative guidance is followed, and it is subsequently found that either – (a) the tested air permeability for that dwelling is equal to or less than 3 m3/(h.m2) at 50 Pa, or (b) where the dwelling is not tested, but another dwelling of the same dwelling type is tested and found to be equal to or less than 3 m3/(h.m2) at 50 Pa, the district council using Part F guidance may require more air permeability testing to be carried out to ensure that all dwellings in the sample are provided with adequate ventilation provision.