How to count insulation panels, fixings and adhesive

1. Area to insulate

For a roof or a floor, multiply the length by the width. For a wall, multiply the length by the height and subtract the doors and windows.

2. Panels, with waste

Increase the area by the waste for cuts, divide by the area of one panel and round up to a whole panel. A 60 × 120 cm panel covers 0.72 m².

3. Fixings, adhesive and vapour barrier

Fixings and adhesive are counted per square metre at the rate the maker gives. The vapour barrier covers the area plus its overlaps, when the build-up needs one.

Worked example: wall 12 × 2.8 m, 6 m² of openings

Panels 60 × 120 cm, 50 mm thick, 8 % waste, 6 fixings and 4 kg of adhesive per m², 10 % overlap:

• Area 12 × 2.8 − 6 = 27.6 m².
• Panels: 27.6 × 1.08 / 0.72 = 41.4, so 42 panels.
• Fixings: 27.6 × 6 = 165.6, so 166. Adhesive: 27.6 × 4 = 110.4 kg.
• Volume 27.6 × 0.05 = 1.38 m³. Vapour barrier 27.6 × 1.10 = 30.36 m².

Second case: a roof 10 × 8 m

Same panels, 8 % waste, without adhesive and without vapour barrier:

• Area 10 × 8 = 80 m².
• Panels: 80 × 1.08 / 0.72 = 120 exactly, so 120 panels, covering 86.4 m².
• Fixings: 80 × 6 = 480. Volume 80 × 0.05 = 4 m³.
• A roof needs no adhesive in this method: untick the vapour barrier if your build-up has none.

What this does not cover

The count gives no thermal resistance or U-value. The thickness, the type of insulation, the condensation and the fire requirements come from a thermal study and the maker’s data.