Multifoil: the one insulation that goes on the rafters
Wools and boards belong on the loft floor. The only insulation we fix to the rafters is thin multifoil, where the roof space is used or there’s no room below.
Illustration: multifoil fixed across the rafters in a room in the roof
| What it is | Layers of foil and wadding, a few centimetres thick |
|---|---|
| Where it goes | Fixed to the rafters, with taped joints |
| Good for | Rooms in the roof, tight spaces |
| Watch for | Condensation if fitted without a ventilated gap |
| Fix | Proper air gaps and taped, sealed joints |
When it’s used
If the loft is a room, or there’s no space on the floor, insulation has to go at the roof line. Multifoil is thin enough to do that without losing much headroom.
The risk
Fitted badly, foil can trap moisture against the roof timbers. It needs the right air gaps and sealed joints so warm, damp air doesn’t get behind it.
How we fit it
Fixed across the rafters with battens to keep the air gaps, joints overlapped and taped, edges sealed. Everywhere else in the loft, insulation stays on the floor.
Common questions
Is multifoil enough on its own?
Why not put wool between the rafters?
Tell us what you’ve found. We’ll find the cause.
Describe the problem and we’ll look, explain it and quote the fix in writing. Free.