UK DIY Cost Calculator
Loft Insulation Calculator
Work out how many rolls of loft insulation you need to reach the recommended depth, and the cost. Enter your loft area and the coverage of your chosen rolls.
Your project
Estimate
Estimates are for guidance only. Coverage rates, pack sizes and prices vary by brand — always confirm quantities with your supplier before buying.
Getting to the recommended depth
The current UK recommendation is around 270mm of loft insulation, usually achieved with two layers: the first between the joists, the second laid across them at right angles. If you already have some insulation, you may only need a top-up layer. Choosing one or two layers above sets how much coverage you need, and the roll coverage figure applies per layer.
Don't compress it
Insulation works by trapping air, so squashing it under boards or storage ruins its performance. If you need loft storage, raise the boarding on legs above the insulation rather than crushing it. Leave ventilation gaps at the eaves so the roof space can still breathe.
Frequently asked questions
How much loft insulation do I need?
For the recommended 270mm you effectively insulate the area twice — two layers — so a 48 m² loft needs about 96 m² of coverage. The calculator doubles the area automatically when you choose the full depth.
What depth of loft insulation is recommended?
Around 270mm of mineral wool is the current UK guideline. Older homes often have far less, so a top-up to modern depth is one of the cheapest ways to cut heat loss.
Can I lay insulation over existing?
Yes — laying a fresh layer across the joists over existing insulation is the normal way to reach modern depths. Just don't compress either layer, and keep it clear of any recessed light fittings that aren't rated for cover.
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