24 Cladding the timber frame
An external wall from the tool's Timber walls group. With the layers below it has a U-value of 0.17 W/m²K, is 259.5 mm thick, and has about 21 kgCO₂e/m² of embodied carbon.
- U-value
- 0.17W/m²K
- Overall thickness
- 259.5mm
- Embodied carbon
- 21kgCO₂e/m²
- Fire
- Worst class E
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.17 |
|---|---|---|
| England | 0.26 W/m²K | Meets it |
| Wales | 0.18 W/m²K | Meets it |
| Scotland | 0.17 W/m²K | Meets it |
These are the limits for a single element in a new home. In England a new home usually needs better figures to pass the whole-house target, about 0.18 for walls. All UK U-value limits.
Section, drawn to scale
Layers, outside to inside
| # | Layer | mm | λ, W/mK | R, m²K/W | kgCO₂e/m² | Fire class |
|---|---|---|---|---|---|---|
| 1 | Timber cladding outside the ventilated cavity: not counted | 20 | 0.13 | – | 2.5 | D-s2,d0 |
| 2 | Ventilated cavity behind cladding outside the ventilated cavity: not counted | 25 | – | – | 0 | – |
| 3 | OSB or plywood sheathing | 12 | 0.13 | 0.092 | 3.4 | D-s2,d0 |
| 4 | Mineral wool between studs 035 bridged by timber studs | 140 | 0.035 | 2.843 | 5.9 | A1 |
| 5 | PIR board | 50 | 0.022 | 2.273 | 5.6 | E |
| 6 | Plasterboard | 12.5 | 0.21 | 0.060 | 3.5 | A2-s1,d0 |
| Total, with surface resistances | 259.5 | 5.757 | 20.9 |
U-value worked out to BS EN ISO 6946 from the total resistance. Carbon is stages A1 to A3 for the layers.
Moisture and rain
Free of interstitial condensation No condensation in any month (Heathrow (London), 1 in 10 year). Surface factor 0.96 (needs over 0.71 and at least 0.75).
Rain: Rainscreen for exposure zone 2 (moderate).
Other timber walls
Figures come from the Build-up Atlas'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.