Building physics
Thickness intentInsulation thickness calculator
Estimate the thickness needed to reach a target U-value. Enter the existing assembly resistance, choose the insulation lambda, and the calculator returns the required thickness.
Best for
- Walls
- Roofs
- Floors
How much insulation is needed to reach 0.20 W/m²K?
Start from the target total resistance, subtract the existing assembly resistance, and convert the remaining resistance into thickness for the chosen insulation lambda.
Example build-up
Target U-value 0.20 W/m²K, existing resistance 1.50 m²K/W, insulation lambda 0.035 W/mK.
Formula
Thickness = (1 / U - R existing) × lambda
Thickness cm = thickness m × 100
Enter the thermal target
Calculation note
Use the current thermal resistance of the non-insulation layers.
Thickness is derived from the difference between target and existing resistance.
What each input means
Target U-value
Set the thermal target you want the full assembly to reach.
Existing resistance
Use the resistance already provided by the structure and finishes.
Lambda value
Lower lambda values need less thickness for the same thermal effect.
More insulation pages
Wall insulation thickness calculator
Use the wall-focused reference page for a concrete wall example.
Open pageHow much insulation for brick wall
Switch to a target-U wall example if you want a ready-made reference page.
Open pageHow much insulation for wall
See a generic wall target-U example without material specificity.
Open page