The airtightness of a building is quantified by means of the measured air leakage rate through the building’s envelope in m³/h at a given reference pressure difference, often 50 Pa. The building airtightness may be expressed by other quantities, derived from the air leakage rate at a reference pressure difference, and normalised using, for example, one of the following measures for the size of the building:
- Internal building volume V. At 50 Pa, the associated indicator is called air change rate at 50 Pa and noted n50 [unit h-1].
- Envelope area AE. At 50 Pa, the associated indicator is called air permeability at 50 Pa and noted qE50 (former: q50 in EN 13829) [unit m3/(h.m2)[.
- Net floor area AF. At 50 Pa, the associated indicator is called specific leakage rate and noted qF50, (former: w50 in EN 13829) [unit m3/(h.m2)].
Other indicators of airtightness exist in national regulations.
Posted in: Building Airtightness, Regulation, Standards