Loft roll, 270 mm between and over joists
A pitched roof with the insulation at ceiling level from the tool's Typical UK roofs group. With the layers below it has a U-value of 0.16 W/m²K, is 282.5 mm thick, and has about 9 kgCO₂e/m² of embodied carbon.
- U-value
- 0.16W/m²K
- Overall thickness
- 282.5mm
- Embodied carbon
- 9kgCO₂e/m²
- Fire
- Worst class D
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.16 |
|---|---|---|
| England | 0.16 W/m²K | Meets it |
| Wales | 0.13 W/m²K | Misses by 0.03 |
| Scotland | 0.12 W/m²K | Misses by 0.04 |
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 | Mineral wool loft roll 044 | 170 | 0.044 | 3.864 | 2.5 | A1 |
| 2 | Mineral wool loft roll 044 bridged by joists at 600 mm | 100 | 0.044 | 1.933 | 2.5 | A1 |
| 3 | Plasterboard | 12.5 | 0.21 | 0.060 | 3.5 | A2-s1,d0 |
| Total, with surface resistances | 282.5 | 6.280 | 8.5 |
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
Not checked Cold pitched roofs with insulation at ceiling level are governed by air leakage into the loft, so BS 5250 13.3 says the Glaser method is unsuitable. Make the ceiling airtight and ventilate the loft.
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.