Maximum
England
Limiting air permeability for a new dwelling
8 m³/(h·m²) at 50 Pa
New dwelling air pressure test at completion
Worst air permeability allowed on test for a new dwelling, regardless of the design figure used in the calculation.
Basis in regulation
How to check it on site
Walk the airtightness line before plaster: service penetrations, loft hatch, and the joist ends at separating walls are where the result is won or lost.
Common failure
Design figure of 5 assumed in the calculation but a tested result well above it, forcing a re-test or remedial sealing after decoration.
Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.