Roof Insulation Quantity Calculator
Estimate insulation boards or rolls for a roof while keeping area, unit size, thickness and cutting allowance visible for procurement.
Insulation inputs
Roof insulation requirement
Roof insulation quantity formula
Theoretical quantity = roof area ÷ unit coverage
Planning quantity = ceiling(theoretical × (1 + waste))
Worked example
If the roof is 180 m² and each board covers 1.2 × 2.4 = 2.88 m², the mathematical minimum is 62.5 boards, before cutting allowance and rounding to full units.
Thickness and quantity are different variables
A 100 mm board and a 150 mm board can have the same footprint but different thermal properties. The calculator keeps thickness visible so the procurement record is unambiguous without pretending to determine the required insulation performance.
Cutting efficiency
Simple rectangular roofs can use material efficiently, while hips, valleys, penetrations and irregular perimeter conditions can create more offcuts. A modest allowance is therefore kept explicit.
Limitations
This tool does not determine required R-value, U-value, condensation control, fire classification or the correct insulation product for a building assembly.
Frequently Asked Questions
Does thickness affect the number of boards?
Not the footprint count when board dimensions remain unchanged.
Should I add waste?
Yes when the layout justifies it.
Can it estimate rolls?
Yes; the same coverage logic is used.
Does it calculate thermal performance?
No.