38 Planted
A flat roof from the tool's Concrete roofs group. With the layers below it has a U-value of 0.14 W/m²K, is 546 mm thick, and has about 117 kgCO₂e/m² of embodied carbon.
- U-value
- 0.14W/m²K
- Overall thickness
- 546mm
- Embodied carbon
- 117kgCO₂e/m²
- Fire
- Worst class E
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.14 |
|---|---|---|
| England | 0.16 W/m²K | Meets it |
| Wales | 0.13 W/m²K | Misses by 0.01 |
| Scotland | 0.12 W/m²K | Misses by 0.02 |
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 | Planting and growing medium | 150 | – | 0.000 | 5.4 | E |
| 2 | Drainage and filter layer | 25 | – | 0.000 | 2.5 | E |
| 3 | Bitumen felt or roofing membrane | 5 | 0.23 | 0.022 | 2.4 | E |
| 4 | PIR board | 150 | 0.022 | 6.818 | 16.7 | E |
| 5 | Bitumen felt or roofing membrane | 3 | 0.23 | 0.013 | 1.4 | E |
| 6 | Reinforced concrete | 200 | 2.3 | 0.087 | 86.4 | A1 |
| 7 | Plaster, dense | 13 | 0.57 | 0.023 | 2.0 | A1 |
| Total, with surface resistances | 546 | 7.103 | 116.8 |
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
Fails: condensate builds up year on year Up to 0 g/m² at , with some left after 12 months. Surface factor 0.96 (needs over 0.72 and at least 0.75).
Rain: Not checked for exposure zone 2 (moderate).
Other concrete 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.