Limiting fabric U-values for a new dwelling

Roof 0.16; wall 0.26; floor 0.18; party wall 0.20; window, roof window and door 1.60 W/(m²·K)

New dwelling, individual element limiting standard

Worst individual U-values allowed for each element of a new dwelling, whatever the overall calculation shows.

Basis in regulation

Part L
Approved Document L
Read the source

How to check it on site

Check the constructions actually built against the compliance report element by element — a substituted block or a thinner board changes the figure.

Common failure

Insulation thickness reduced on site to close a cavity, leaving the wall outside the limiting value even though the design passed.

Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.

Related dimensions at this stage

Maximum

Limiting air permeability for a new dwelling

8 m³/(h·m²) at 50 Pa

New dwelling air pressure test at completion

Minimum

AVCL jointing requirements

100 mm

Joints in air and vapour control membranes must be adequately lapped, typically with a minimum overlap of 100mm, to ensure continuity of the membrane

Minimum

Clearance for walkways above insulation

50 mm

Boarded walkways and working platforms within roof spaces must be securely fixed and maintain a minimum 50mm clearance above the insulation