Wood fibre over rafters, mineral wool between
A pitched roof with the insulation at the rafters from the tool's Typical UK roofs group. With the layers below it has a U-value of 0.17 W/m²K, is 294.5 mm thick, and has about 37 kgCO₂e/m² of embodied carbon.
- U-value
- 0.17W/m²K
- Overall thickness
- 294.5mm
- Embodied carbon
- 37kgCO₂e/m²
- Fire
- Worst class E
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.17 |
|---|---|---|
| England | 0.16 W/m²K | Misses by 0.01 |
| Wales | 0.13 W/m²K | Misses by 0.04 |
| Scotland | 0.12 W/m²K | Misses by 0.05 |
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 | Roof tiles, clay outside the ventilated cavity: not counted | 15 | 1 | – | 13.7 | A1 |
| 2 | Ventilated cavity behind cladding outside the ventilated cavity: not counted | 25 | – | – | 0 | – |
| 3 | Wood fibre board | 80 | 0.04 | 2.000 | 11.0 | E |
| 4 | Mineral wool between studs 035 bridged by joists at 600 mm | 150 | 0.035 | 3.444 | 5.4 | A1 |
| 5 | OSB or plywood sheathing | 12 | 0.13 | 0.092 | 3.4 | D-s2,d0 |
| 6 | Plasterboard | 12.5 | 0.21 | 0.060 | 3.5 | A2-s1,d0 |
| Total, with surface resistances | 294.5 | 5.970 | 36.9 |
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
Free of interstitial condensation No condensation in any month (Heathrow (London), 1 in 10 year). Surface factor 0.96 (needs over 0.72 and at least 0.75).
Rain: Not checked for exposure zone 2 (moderate).
Other typical UK 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.