Calculate the amount of insulation rolls, batts, or boards needed for walls, floors and lofts.
This insulation calculator works out how much insulation you need by area, and helps you choose a thickness for lofts (attics), walls and floors. It works with rolls, batts (slabs) and boards, in metric or imperial, using both UK depths (mm) and US R-values.
| Location | UK depth | US R-value |
|---|---|---|
| Loft / attic | 270 mm | R-38 to R-49 |
| Cavity wall | 50–100 mm | R-13 to R-21 |
| Suspended floor | 100 mm | R-19 to R-25 |
A loft of 50 m² needing 270 mm often uses a first layer between the joists and a second layer laid across them. Rolls state their coverage per pack, so divide the area by the pack coverage and round up.
Measure the loft floor area and divide by the roll coverage area. Standard UK loft insulation is 270 mm thick.
R-38 to R-60 for attics, R-13 to R-23 for walls, R-25 to R-30 for floors in most US climate zones.
Yes, as long as the existing insulation is dry and in good condition. Lay the new rolls perpendicular to the old.
Lay the first layer between the joists, then a second layer at right angles across the joists to cover the cold bridges. Keep insulation clear of eaves vents and recessed lights.
Current UK guidance is around 270 mm of mineral wool for a loft; walls and floors use thinner boards or batts to suit the cavity.
