Straw bale with lime render and clay plaster
An external wall from the tool's Lower-carbon walls group. With the layers below it has a U-value of 0.14 W/m²K, is 510 mm thick, and has about 14 kgCO₂e/m² of embodied carbon.
- U-value
- 0.14W/m²K
- Overall thickness
- 510mm
- Embodied carbon
- 14kgCO₂e/m²
- Fire
- Worst class E
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.14 |
|---|---|---|
| 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 | Lime render | 30 | 0.8 | 0.037 | 9.6 | A1 |
| 2 | Straw bale | 450 | 0.065 | 6.923 | 2.5 | E |
| 3 | Clay plaster | 30 | 0.8 | 0.037 | 1.5 | A1 |
| Total, with surface resistances | 510 | 7.168 | 13.6 |
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 0.97 (needs over 0.71 and at least 0.75).
Rain: Face-sealed for exposure zone 2 (moderate).
Other lower-carbon 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.