Loft insulation calculator: how many rolls do I need?
Multiply the loft floor area by the number of layers, divide by the coverage printed on the roll, and round up. The Energy Saving Trust recommends a total depth of 270 mm for mineral wool, which usually means one layer between the joists and one across them.
Example: A 40 m² loft with two layers, using rolls that cover 8 m² each, needs 80 ÷ 8 = 10 rolls. Check the coverage on the actual product, because it varies by brand and thickness.
How to use it
- Measure the length and width of the loft floor and multiply them
- Read the coverage per roll from the pack or product sheet
- Choose one or two layers
- Add the result to your list and send it for a quote
These are estimates for planning and pricing, not specifications. Check quantities against your drawings, and follow your builder, engineer or the manufacturer’s guidance. Allan will check the quantities with you before anything is ordered.
Common questions
How thick should loft insulation be?
The Energy Saving Trust recommends 270 mm of mineral wool loft insulation. Many lofts have less, so topping up to that depth is a common job.
Why lay loft insulation in two layers?
The first layer fills the space between the joists. The second runs across the joists, covering them so heat doesn’t escape through the timber and the full depth is reached.
Can I board over loft insulation?
Not directly, or it gets squashed and works less well. Raise the boards on loft legs so the full depth of insulation sits underneath.
Get it priced
- Nothing added yet. Use a calculator and press "Add to my list".