Building airtightness

This air leakage is driven by differential pressures across the building envelope due to the combined effects of stack, external wind and mechanical ventilation systems.

Conversely, poor airtightness may prevent achieving the desired indoor temperature conditions if the equipment has not been sized with proper estimates of infiltration heat losses.

[9] This adverse effect has been confirmed by numerical simulations in the French context which has shown that typical mechanical ventilation systems yielded better indoor air quality with tighter envelopes.

It represents the area of a perfect orifice that would produce the same airflow rate as that passing through the building envelope at the reference pressure.

There are several countries (e.g., United Kingdom, France, Portugal, Denmark, Ireland) where, by regulation, airtightness testing is mandatory for certain building types or in the case of specific programmes.

Historically, the Passivhaus standard, originated in 1988 was the cornerstone for envelope airtightness developments because these types of buildings require extremely low leakage levels (n50 below 0.6 ach).