Target U-value
Pitched roof intentHow much insulation for pitched roof?
A pitched roof usually needs enough insulation to reach the target U-value without exceeding the available build-up depth.
Best for
- Warm roofs
- Pitched roofs
- Roof rebuilds
Worked example
How much insulation is needed to reach 0.18 W/m²K?
Roof calculations are sensitive to the existing roof deck resistance, so this page keeps the example simple and direct.
Example build-up
Target U-value 0.18 W/m²K, existing roof resistance 1.70 m2K/W, insulation lambda 0.035 W/mK.
Result
Required insulation thickness is approximately 10.6 cm.
Roof notes
Why pitched roofs need care
Available depth
The rafter depth may limit the thickness you can fit.
Ventilation layer
Some roof types need a ventilated gap that changes the build-up.
Thermal bridge control
The target value is not only about thickness; details around junctions matter too.
Related pages