Tolerance
England
Flatness of a finished plasterboard surface
Within 3 mm under a 1.8 m straightedge
Measured on the finished surface in any direction, away from internal corners
A finished wall or ceiling should be flat enough that a straightedge or low-angle light does not pick up hollows and ridges.
Basis in regulation
How to check it on site
Check with a raking light before decoration — paint makes deviations more obvious, not less.
Common failure
Dabs set to a poorly aligned wall, so the finished plane wanders across the room.
Effective from 22 August 2026. Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.