Arbutus

Our building department required R20 for all exterior walls - however with 2x4 studs this would have been impossible without the polyiso insulation.

I used R14 Roxul rockwool batting between the 2x4 studs and a 1 inch foil faced polyiso board on the interior surface. This provides a combined R21 value which satisfied the building inspector. All seams were taped with foil tape so the vapor barrier was intact. Interior sheathing was 1/2" G1S fir ply.

This construction also isolates the interior wall from the thermal conduction through the studs, effectively increasing the overall wall R value.