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Air tightness measured as n50 or q50 for passive house: UK and Passivhaus methodology!
January 8, 2016

Air tightness measured as n50 or q50 for passive house: UK and Passivhaus methodology!

Passive house methodology (n50) states that the Passive house standard measures the Air Change Rate (ACH) @50Pa (the n50 measurement), or in other words the number of times the volume of air within the building is changed in an hour. So, it is a purely volumetric measure. The Passive houses methodology considers the volume of air which needs to be heated. Therefore internal walls and floors are excluded. This is a measure of air infiltration, and hence the heating energy cost of the building.

UK methodology (q50) states that the Building Regulations requires air tightness to be measured as Air Permeability, in m3/h/m2@50Pa (the q50 measurement), or in other words the air leakage per square meter of building envelope. The ATTMA (Air Tightness Testing and Measurement Association) TS1 standard defines the building envelope as everything within the air barrier line‘ along the line of the component to be relied upon for air sealing’. This could be anywhere within the building envelope (even the external render). This is a measure of building envelope air tightness.

The criterion for passive house certification relating to air tightness requires that n50 ≤ 0.6 h-1@ 50Pa. The target is the same for EnerPHit, however, if the target is not achieved even though remedial measures are taken after an initial test then there is a back stop limit of n50≤1.0 h-1@ 50Pa. There is also a q50 requirement for large buildings, where the air volume is in excess of 4,000 m3.

Test method includes both n50 and q50 are calculated from a measurement of the airflow (V50) at 50Pa. The measurement of airflow should be carried out in accordance with EN13829 and ATTMA Technical Standard TSL1 for dwellings and TSL2 for non-dwellings. For Building Regulation compliance testing: q50=V50/Ae. Where Ae is the building envelope area as defined by EN 13829.

For Passive house compliance testing: n50=V50/V. Where V is the building air volume as defined by DIN 4108-7.