19 Masonry cavity walls, block
An external wall from the tool's Masonry walls group. With the layers below it has a U-value of 0.18 W/m²K, is 378 mm thick, and has about 51 kgCO₂e/m² of embodied carbon.
- U-value
- 0.18W/m²K
- Overall thickness
- 378mm
- Embodied carbon
- 51kgCO₂e/m²
- Fire
- A2 or better
Against the Building Regulations
| New home in | U-value limit | This build-up, 0.18 |
|---|---|---|
| England | 0.26 W/m²K | Meets it |
| Wales | 0.18 W/m²K | Meets it |
| Scotland | 0.17 W/m²K | Misses by 0.01 |
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, about 0.18 for walls. 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 | Sand-cement render | 15 | 1 | 0.015 | 5.7 | A1 |
| 2 | Dense concrete block | 100 | 1.13 | 0.088 | 20.0 | A1 |
| 3 | Mineral wool cavity batt 032 | 150 | 0.032 | 4.688 | 6.1 | A1 |
| 4 | Aircrete block, standard bridged by mortar joints | 100 | 0.15 | 0.503 | 16.8 | A1 |
| 5 | Plaster, dense | 13 | 0.57 | 0.023 | 2.0 | A1 |
| Total, with surface resistances | 378 | 5.548 | 50.6 |
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 1002 g/m² at between dense concrete block and mineral wool cavity batt 032 (part 1 of 19), with some left after 12 months. Surface factor 0.95 (needs over 0.71 and at least 0.75).
Rain: Zone 2 of max 4 for exposure zone 2 (moderate).
Other masonry walls
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.