Wall Insulation Board Calculator
Calculate wall insulation boards from gross wall dimensions, door and window openings, board size and cutting allowance.
Wall and board inputs
Wall insulation requirement
Wall insulation board formula
The net wall area is divided by the footprint area of one board, then a project-specific cutting allowance is applied.
Net area = gross area − openings
Board area = board width × board length
Order quantity = ceiling(net area ÷ board area × (1 + waste))
Worked example
A 12 × 3 m wall contains 36 m² gross area. After 7 m² of openings, 29 m² remains. With 1.2 × 2.4 m boards, each board covers 2.88 m² before cuts.
Why the board count is not the whole design
Board joints, thermal bridges, fixing pattern, vapour control and fire performance all depend on the specified assembly. Quantity estimating should follow those requirements rather than determine them.
Openings and waste
Openings reduce area but can increase cutting waste. The allowance is therefore a practical planning assumption, not a mathematical correction for every individual opening.
Frequently Asked Questions
Should windows be deducted?
Yes when they are outside the insulation scope.
Does board thickness change the area count?
No, unless footprint dimensions also change.
Is waste necessary?
Usually a project-specific allowance is sensible.
Does this determine thermal compliance?
No.