Foil insulation fire rating: what the classification does and does not tell you

Reaction-to-fire classes

BS EN 13501-1 classes construction products from A1 (non-combustible) to F, with smoke (s1–s3) and droplet (d0–d2) suffixes. Typical multifoils — polyester wadding, foams, aluminium or metallised films — are combustible products and are commonly classified in the E range; some manufacturers offer specific non-combustible or improved-class multifoil variants. The exact class for a product is on its declaration of performance and certificate, and it is the only figure to rely on.

Product class ≠ construction performance

A roof's fire performance is assessed for the whole build-up. The internal lining — usually plasterboard of a stated thickness — provides the fire resistance to the room, and certificates for multifoil build-ups typically specify that lining. A Class E quilt behind 12.5mm plasterboard on battens is a normal, certified arrangement; the same quilt left exposed is not.

What the certificate and regulations require

• The certified build-up states the lining required over the quilt and any limits on exposure.
• Approved Document B sets requirements for internal linings and, where relevant, for roofs near boundaries and for loft conversions (escape, fire resistance of floors).
• Loft conversions add fire requirements well beyond the insulation: protected escape routes, fire doors, floor fire resistance.

Practical rules

• Never leave multifoil exposed in a habitable room or an escape route.
• Keep clearances from flues, recessed downlighters and other heat sources per the appliance and product instructions.
• Use the fire-rated tape and detailing the manufacturer specifies where the certificate calls for it.
• Ask for the declaration of performance, not a brochure line.

Questions homeowners ask