The Passivhaus airtightness target is < 0.6 ACH-1 @ 50 Pa for newbuild projects and < 1.0 ACH-1 @ 50 Pa for EnerPHit refurbishment projects. This compares with UK Building Regulations, where a maximum air permeability of 10m3/hr/m2 @ 50 Pa is commonly permitted. Hence the Passivhaus airtightness requirements for new build are some 15 times more onerous than UK Building Regulations, while insulation requirements will typically only be 3 to 4 times more demanding than Building Regulations. Therefore it is not surprising that UK contractors often find the stringent Passivhaus airtightness requirements particularly difficult to meet.
The quoted targets are the final acceptance value; it is sensible to leave a margin to allow for the leakage often found around services that are installed after the first airtightness test. This should be at least 25%, which means aiming for preliminary test results of:
• < 0.45 ACH-1 @ 50 Pa for newbuild projects
• < 0.75 ACH-1 @ 50 Pa for refurbishment projects