Roof - Sloping / Pitched Roof - Timber - Input Required  help

Breather membrane

If unticked, i.e. a non-breather membrane is used such as felt, then a minimum 50mm vented airspace between the joists/rafters is required and so must be allowed for when selecting the thickness of insulation located between the joists/rafters.

Rafter width

 mm

Rafter depth

 mm

Rafter centres

 mm

Finish/Insulation below rafter


You can either select an insulation or enter the
target U-value you want to achieve below...

Insulation between joists 

or Target U-value  W/m²k


Hover over me

Calculate U‑value

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