20 Stone cladding
An external wall from the tool's Masonry walls group. With the layers below it has a U-value of 0.25 W/m²K, is 457.5 mm thick, and has about 110 kgCO₂e/m² of embodied carbon.
- U-value
- 0.25W/m²K
- Overall thickness
- 457.5mm
- Embodied carbon
- 110kgCO₂e/m²
- Fire
- A2 or better
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.25 |
|---|---|---|
| England | 0.26 W/m²K | Meets it |
| Wales | 0.18 W/m²K | Misses by 0.07 |
| Scotland | 0.17 W/m²K | Misses by 0.08 |
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 | Limestone cladding panel outside the ventilated cavity: not counted | 40 | 1.7 | – | 8.6 | A1 |
| 2 | Ventilated cavity behind cladding outside the ventilated cavity: not counted | 40 | – | – | 0 | – |
| 3 | Mineral wool rainscreen slab | 150 | 0.035 | 4.286 | 11.5 | A1 |
| 4 | Reinforced concrete | 200 | 2.3 | 0.087 | 86.4 | A1 |
| 5 | Unventilated cavity or dab gap | 15 | – | 0.171 | 0 | – |
| 6 | Plasterboard | 12.5 | 0.21 | 0.060 | 3.5 | A2-s1,d0 |
| Total, with surface resistances | 457.5 | 4.863 | 110.1 |
U-value worked out to BS EN ISO 6946 from the total resistance, plus 0.040 W/m²K of corrections for fixings, gaps or brackets. 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 0.94 (needs over 0.71 and at least 0.75).
Rain: Zone 2 of max 4 for exposure zone 2 (moderate).
Other masonry 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.