29 Rainscreens
A pitched roof with the insulation at the rafters from the tool's Metal roofs group. With the layers below it has a U-value of 0.18 W/m²K, is 216 mm thick, and has about 109 kgCO₂e/m² of embodied carbon.
- U-value
- 0.18W/m²K
- Overall thickness
- 216mm
- Embodied carbon
- 109kgCO₂e/m²
- Fire
- Worst class E
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.18 |
|---|---|---|
| England | 0.16 W/m²K | Misses by 0.02 |
| Wales | 0.13 W/m²K | Misses by 0.05 |
| Scotland | 0.12 W/m²K | Misses by 0.06 |
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. 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 | Aluminium rainscreen panel outside the ventilated cavity: not counted | 3 | 160 | – | 54.0 | A1 |
| 2 | Ventilated cavity behind cladding outside the ventilated cavity: not counted | 60 | – | – | 0 | – |
| 3 | Single-ply membrane | 2 | 0.2 | 0.010 | 8.1 | E |
| 4 | PIR board | 150 | 0.022 | 6.818 | 16.7 | E |
| 5 | Profiled steel structural deck | 1 | 50 | 0.000 | 21.7 | A1 |
| Total, with surface resistances | 216 | 7.028 | 108.8 |
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, including 8.3 kgCO₂e/m² for steel rails or purlins.
Moisture and rain
Traces only Under 10 g/m² at most, which the tool treats as negligible. Surface factor 0.95 (needs over 0.72 and at least 0.75).
Rain: Not checked for exposure zone 2 (moderate).
Other metal roofs
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.