Do multifoil insulations need air gaps?

Yes — multifoil insulations rely on reflective air gaps on both sides to achieve their stated thermal performance. Without air gaps, the foil layers cannot reflect radiant heat and the insulation performs poorly. A minimum 25mm unventilated air gap is needed on each side, created by fixing battens before and after the multifoil. This is a critical installation requirement.

What R-value does multifoil insulation achieve?

Multifoil insulations typically achieve R-values of 1.4-2.8 m²K/W including air gaps, depending on the number of layers and construction. This is equivalent to about 30-60mm of PIR board. They cannot achieve the thermal performance of thick rigid insulation on their own — they're best used as a supplementary layer in combination with other insulation to boost overall U-value.

Can multifoil insulation replace conventional insulation?

Multifoil insulation alone is unlikely to achieve Part L U-values for walls or roofs. It's best used as part of a hybrid system — for example, mineral wool between rafters plus multifoil under the rafters with an air gap. The multifoil adds reflective insulation and acts as a vapour barrier. Claims of very high R-values for thin multifoils have been disputed by the BBA.

How many staples per m² for multifoil?

Use approximately 8 staples per m² to secure multifoil insulation to timber battens. Use stainless steel staples (10-14mm) to prevent corrosion against the foil. All joints should overlap by at least 100mm and be sealed with aluminium foil tape. The foil must be taut with no sagging — sagging reduces air gap performance and can trap condensation.

Is multifoil insulation BBA certified?

Some multifoil products have BBA certificates, but the certified performance values are often lower than manufacturer claims. Check the specific BBA certificate number and the tested R-value with air gaps as installed. Building Control may not accept manufacturer claims without third-party certification. Products like SuperFOIL, TLX Silver, and YBS BreatherFoil have BBA certificates for specific applications.

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Multifoil Insulation Calculator — Rolls, Battens & Staples

Calculate multifoil insulation quantities including air gap battens on both sides, staple count, and foil tape for sealed joints.

Area to Insulate

Roof slope or wall area

Multifoil Product

Determines R-value

Price Per Roll (optional)

How We Calculate This

This calculator works out multifoil insulation quantities including the battens needed to create reflective air gaps on both sides, staples for fixing, and foil tape for joints.

The formula

Rolls = Ceiling(Area × Lap factor ÷ Roll coverage)

Batten metres = (Area ÷ Spacing) × Air gap sides × Waste

Staples = Area × 8 per m²

Total thickness = Foil + Battens (both sides)

For example, 50 m² roof with standard multifoil, air gaps both sides: Rolls = 50 × 1.07 ÷ 15 = 4 rolls. Battens = (50 ÷ 0.6) × 2 × 1.1 = 183m. Staples = 400. Total thickness = 20 + 25 + 25 = 70mm. R = 1.64 m²K/W.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.