Build up your wall, roof or floor layer by layer, enter each material’s thermal conductivity (λ) and thickness, and the calculator returns total thermal resistance and the resulting U-value. Use it to sense-check a build-up against current Building Regulations targets before it goes into a drawing.
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| Material | λ (W/mK) |
|---|---|
| Brickwork (outer leaf) | 0.77–0.84 |
| Concrete block (medium density) | 1.13 |
| Mineral wool insulation | 0.035–0.044 |
| PIR / PUR insulation board | 0.022–0.028 |
| Plasterboard | 0.21–0.25 |
| Timber (softwood) | 0.13 |
Around 0.18 W/m²K meets current expectations for new build and extensions in England. Existing solid walls often sit above 2.0 W/m²K before insulation, which is why retrofit gains can be so large.
Use it for design decisions and early checks. Formal submissions need a SAP or full elemental calculation from a qualified assessor, which accounts for thermal bridging and junction detail.
Thermal conductivity — how readily a material conducts heat, in W/mK. Lower is better. PIR board sits around 0.022, mineral wool around 0.035–0.044, and dense concrete block above 1.0.
These tools give you a reliable starting figure. When you’re ready to turn it into a costed, fixed-scope proposal, our team works across London, Dubai and Cairo on architecture, interior design and turnkey delivery.
