Quick answer: PIR can be used for loft insulation, but the right product depends on where the insulation layer sits.
For a standard cold loft where the insulation is on the loft floor, loft insulation roll is normally the more practical choice. For a warm loft, loft conversion or sloping roof where the insulation is fitted at rafter level, rigid PIR insulation board can be a better fit.
Use loft roll when insulating the loft floor
In a standard cold loft, the insulation layer is normally at ceiling or loft-floor level, between and over the joists. This keeps the rooms below warm while allowing the loft space above to remain outside the heated envelope.
Mineral wool loft roll is designed for this job and is straightforward to lay across regular joists.
Use PIR when insulating at rafter level
If the roof space itself needs to stay warm, rigid insulation boards can be fitted as part of a suitable pitched-roof build-up between and/or across the rafters.
This is common in loft conversions and warm-roof arrangements where internal space matters and the insulation layer follows the roof slope rather than the loft floor.
PIR is useful where insulation depth is limited
Rigid PIR provides strong thermal resistance for its thickness, so it can be useful where there is limited space within a roof or rafter build-up.
The thickness still needs to come from the complete construction and thermal target. See our PIR U-value and thickness guide.
Keep ventilation and moisture control correct
Moving insulation from the loft floor to rafter level changes how the roof behaves. Ventilation, vapour control and the rest of the roof build-up need to suit the chosen construction.
If the loft or roof already has a damp problem, fix the cause before adding insulation.
Which loft insulation should you buy?
- Standard cold loft floor: shop loft insulation rolls.
- Loft conversion or warm roof at rafter level: shop PIR insulation board.
- Not sure which material suits the job: read PIR vs Mineral Wool Insulation.
