Edge Compression R-value Calculator

Comfortech® has worked with Design Navigator to develop an Edge Compression R-Value Calculator. This calculator allows us to extrapolate the product R-value across the last 500mm of the ceiling or roof perimeter, under compression to ensure you will meet the required R3.3 construction R-value under the 5th Edition of H1.

Note: The calculation assumes that the bottom of the insulation is flush with the top of the top plate across the whole width. In reality there may be a gap between the top of the lining and the top of the top plate. Therefore, the insulation will be less compressed as calculated in this spreadsheet. That calculation is therefore conservative.

Choose from the Pink® Superbatts® product range

We have carried out extensive testing to quantify the performance of the Pink® Superbatts® range under compression; this enables us to deliver an industry leading solution that is proven to perform.

The perimeter width is the width of the insulation segment, i.e. it is counted from the outer edge of the insulation (not the wall framing).


The rise of the rafters. By default, the rafters would sit directly on top of the top plate.

Under NZS4246, a 25mm gap must be maintained between the underside of the roof underlay and the top of the insulation

The insulation is placed halfway across the top plate. This value is the offset of the insulation from the outer side of the top plate.

Not Compliant
Perimeter Insulation Only Average R-Value
Increase heel height to reduce compression
The compression is over too large an area; increase heel height to reduce compression area
Roof Slope
Perimeter width
Total Height at Heel
% max compression
Minimum R value
Truss chord height
Raised Heel Height
Include Roll Panel Vent
Uncompressed insulation thickness
Uncompressed insulation R value
% R-value Reduction per % compression