Rigid boards: slim insulation under a loft floor
Foil-faced boards insulate well for their thickness, so they suit shallow joists or a loft that has to stay boarded. They go on the floor, between the joists.
Illustration: rigid boards fitted between the joists
| What it is | Foil-faced PIR foam boards |
|---|---|
| Where it goes | Cut between the joists on the loft floor |
| Good for | Shallow joists, under a storage floor |
| Watch for | Gaps around the edges letting air past |
| Fix | Tight cuts, sealed edges |
Where they help
If the joists are shallow, or you want a storage floor without raising it, boards give more insulation per centimetre than wool.
Fitted right
Boards only work if they’re cut tightly between the joists and the edges are sealed. Gaps let warm air slip past and can create cold, damp spots.
Where they don’t go
We don’t fix boards to the rafters. In a loft they belong on the floor, between the joists.
Common questions
Are boards better than wool?
Thinner for the same effect, but more expensive and fussier to fit. Wool suits most lofts.
Can you put boards under my existing boarding?
Yes, by lifting the boards and fitting insulation between the joists.
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.