42 GRP panels and shells
A flat roof from the tool's Polymer roofs group. With the layers below it has a U-value of 0.22 W/m²K, is 130 mm thick, and has about 154 kgCO₂e/m² of embodied carbon.
- U-value
- 0.22W/m²K
- Overall thickness
- 130mm
- Embodied carbon
- 154kgCO₂e/m²
- Fire
- Worst class E
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.22 |
|---|---|---|
| England | 0.16 W/m²K | Misses by 0.06 |
| Wales | 0.13 W/m²K | Misses by 0.09 |
| Scotland | 0.12 W/m²K | Misses by 0.10 |
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 | GRP panel skin | 5 | 0.3 | 0.017 | 68.8 | E |
| 2 | Polyurethane foam core | 120 | 0.028 | 4.286 | 16.7 | E |
| 3 | GRP panel skin | 5 | 0.3 | 0.017 | 68.8 | E |
| Total, with surface resistances | 130 | 4.459 | 154.4 |
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
Condenses in winter, dries by summer Up to 20 g/m² at between grp panel skin and polyurethane foam core (part 1 of 18), all of it drying out over the year. Surface factor 0.94 (needs over 0.72 and at least 0.75).
Rain: Not checked for exposure zone 2 (moderate).
Other polymer 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.