Building Physics
Tool for quick thermal analysis of assemblies
Lambda Calculator
Choose a material, enter layer thickness, and calculate thermal properties for the full assembly.
Scope
Walls, roofs, floors, slabs
One place to select material, thickness, and verify U-value.
Assembly Builder
Add layers, choose materials, and update results live.
Surface Resistance
Results
Summary metrics and a layer table ready for print or export.
| Layer | Category | Material | Thickness | Lambda | R |
|---|
Formulas
R = d / lambda
U = 1 / (Rsi + sum(R layers) + Rse)
Notes
Thickness is entered in millimeters and converted to meters internally.
Material lambda values are indicative and should be verified in technical data sheets.
FAQ
Lambda is the thermal conductivity of a material, usually shown in W/mK. Lower lambda means heat moves through that material more slowly, but the final assembly still depends on thickness, surface resistances, and every other layer.
U-value describes heat loss through the whole building element, not just one material. A low U-value usually means a better insulated wall, roof, or floor, provided the real build-up matches the layers entered in the calculator.
Yes. Use the comparison section to keep thickness constant, then compare materials by lambda and calculated thermal resistance. This is useful when two products look similar on paper but behave differently at the same installed depth.
Yes. You can print the result or export it to CSV, Excel, or PDF for reports and documentation.
Yes. It is designed for layered assemblies such as external walls, flat roofs, pitched roofs, floors, and slabs. For unusual assemblies, add every relevant layer and treat the result as a planning check before formal verification.
Yes. It is intended for fast concept-stage calculations, insulation comparison, and envelope optimisation before detailed design. It is best used to narrow choices, not to replace a code check or project-specific thermal bridge assessment.
Yes. You can switch between millimeters, centimeters, and inches, and the calculator keeps the values consistent. For fewer mistakes, choose one unit system at the start of a project and review converted thicknesses before export.