UK U-value limits for walls, roofs, floors and windows

The highest U-value each element may have under the energy rules in England, Wales and Scotland, in W/m²K. Lower is better insulated. These are the figures the Wall Build-up Visualiser checks against.

Check a build-up against these limits U-values of common build-ups

England

Element	New homes	Extensions to homes	Upgraded elements in homes	Other new buildings
External walls	0.26	0.18	0.30	0.26
Pitched roofs	0.16	0.15	0.16	0.16
Flat roofs	0.16	0.15	0.16	0.18
Floors	0.18	0.18	0.25	0.18
Windows and glazed walls	1.60	1.40	1.40	1.60
Rooflights	2.20	2.20	2.20	2.20

From England, Approved Document L 2021; England, Approved Document L 2021, Volume 2. New homes in England are limiting values: to pass the whole-house target a new home usually needs about 0.18 for walls, 0.11 for roofs and 0.13 for floors. "See note" means the tool has no figure loaded for that case: check the current document.

Wales

Element	New homes	Extensions to homes	Upgraded elements in homes	Other new buildings
External walls	0.18	0.18	see note	see note
Pitched roofs	0.13	0.13	see note	see note
Flat roofs	0.13	0.13	see note	see note
Floors	0.15	0.15	see note	see note
Windows and glazed walls	1.40	1.40	see note	see note
Rooflights	2.20	2.20	see note	see note

From Wales, Approved Document L 2022. Flats may use 0.21 for walls. "See note" means the tool has no figure loaded for that case: check the current document.

Scotland

Element	New homes	Extensions to homes	Upgraded elements in homes	Other new buildings
External walls	0.17	see note	see note	see note
Pitched roofs	0.12	see note	see note	see note
Flat roofs	0.12	see note	see note	see note
Floors	0.15	see note	see note	see note
Windows and glazed walls	1.40	see note	see note	see note
Rooflights	1.40	see note	see note	see note

From Scotland, Technical Handbook Section 6, 2023 standards. New homes are the maximum area-weighted average. "See note" means the tool has no figure loaded for that case: check the current document.

Regulations change. Always check the current edition of the Approved Document or Technical Handbook for your project, and whether a whole-building calculation sets a tighter target.

Figures come from the Wall Build-up Visualiser's own calculation, with generalised values for typical products, for an England new home with default settings. They are indicative, for design and teaching: check the manufacturer's declared values and the current regulations for your project. Rules and standards last checked 21 October 2026.