U-value ≤ 0.30 for external walls, ≤ 0.20 for roofs and ground floors, energy frame 30 kWh/m²/year for dwellings — the concrete BR18 figures the carpenter needs to know, and how to calculate them.
Introduction
The climate envelope — exterior walls, roof/ceiling, windows and terrain deck — is the carpenter's domain. BR18 Chapter 11 sets the minimum U-values allowed in new construction and an energy frame that limits total heating demand.
U-value requirements (new construction)
| Building part | Minimum requirements (new construction) | Indicative tightening (renovation) |
|---|---|---|
| Exterior wall | U ≤ 0,30 W/m²K | U ≤ 0,18 W/m²K |
| Ceiling/roof against unheated room | U ≤ 0,20 W/m²K | U ≤ 0,12 W/m²K |
| Ground deck against earth | U ≤ 0,20 W/m²K | U ≤ 0,10 W/m²K |
| Windows and exterior doors | U ≤ 1,80 W/m²K | U ≤ 1,40 W/m²K |
Source: BR18 §§ 250–298, verified via bygningsreglementet.dk.
The U-value formula
Eksempel: let træskeletvæg (udefra ind): 22 mm facadebræt (λ = 0,12), 9 mm vindspærreplade (λ = 0,14), 195 mm mineraluldsisolering (λ = 0,036), 12,5 mm gips (λ = 0,22). R_total = 0,04 + 22/120 + 9/140 + 195/36 + 12,5/220 + 0,13 = 0,04 + 0,18 + 0,06 + 5,42 + 0,06 + 0,13 ≈ 5,89 m²K/W → U ≈ 0,17 W/m²K. Langt under de 0,30, og nær renoveringsskærpelsen.
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