Loft Insulation Calculator
Work out how many insulation rolls or boards you need for a loft.
Rolls or boards required
7units
- Area covered
- 50 m²
v1.0 · Reviewed September 2026
How this is worked out
The loft area is increased by any waste allowance, divided by the coverage of one roll or board, and rounded up to a whole number.
Worked example
- 50 m² loft
- 8 m² per roll
- no waste allowance
50 ÷ 8 = 6.25, rounded up
7 rolls
Assumptions and limits
- Coverage comes from the pack, and varies with thickness. The recommended depth is 270 mm, usually laid as one layer between the joists and a second across them, which needs two passes of material.
- Rounds up to whole rolls, since you cannot buy part of one.
- Do not insulate under a cold water tank, and keep eaves ventilation clear to avoid condensation.