15 Cast in situ
An external wall from the tool's Concrete walls group. With the layers below it has a U-value of 0.21 W/m²K, is 500 mm thick, and has about 171 kgCO₂e/m² of embodied carbon.
- U-value
- 0.21W/m²K
- Overall thickness
- 500mm
- Embodied carbon
- 171kgCO₂e/m²
- Fire
- Worst class E
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.21 |
|---|---|---|
| England | 0.26 W/m²K | Meets it |
| Wales | 0.18 W/m²K | Misses by 0.03 |
| Scotland | 0.17 W/m²K | Misses by 0.04 |
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 | Reinforced concrete | 150 | 2.3 | 0.065 | 64.8 | A1 |
| 2 | XPS board | 150 | 0.034 | 4.412 | 19.3 | E |
| 3 | Reinforced concrete | 200 | 2.3 | 0.087 | 86.4 | A1 |
| Total, with surface resistances | 500 | 4.734 | 170.5 |
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
Traces only Under 10 g/m² at most, which the tool treats as negligible. Surface factor 0.95 (needs over 0.71 and at least 0.75).
Rain: Zone 2 of max 4 for exposure zone 2 (moderate).
Other concrete 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.