Loft roll calculator

Work out how many loft rolls you need. Enter your loft floor area, choose a roll and thickness from the loft rolls we stock (ODE, Knauf Insulation and URSA) and set the number of layers. We use the coverage printed on each roll, add a waste allowance, round up to whole rolls and price it live, ex and inc VAT.

Topping up an existing loft? Enter the thickness you’re adding, not the total. Most lofts are done in two layers: one between the joists and one laid across them.

Your job

Area
The area to be insulated, in square metres.
e.g. 2 for a loft topped up across the joists.
For cutting and offcuts. 10% suits most jobs.

Your insulation

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Prefer to browse? See every loft roll we stock.

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Estimate only. Quantities are based on the area you enter and the coverage of each sheet, pack or roll as sold. They don’t allow for the space taken by joists, studs or rafters, awkward shapes or extra layers you haven’t entered. Check the thickness you need for Building Regulations with your builder, building control or the manufacturer’s literature. Call us on 03330 908479 and we’ll happily check it before you order.

How to use the loft roll calculator

  1. Measure the loft floor (length × width of the area between the eaves you’re insulating) or enter the area in m².
  2. Pick a loft roll and thickness. Each roll’s coverage is shown under the thickness.
  3. Doing two layers in different thicknesses? Work out each layer separately with Layers set to 1, and add each to your basket.
  4. Keep the waste at 10% unless the loft is very cut up by water tanks, chimneys or trusses.

How we calculate

  • Coverage is the m² per roll shown in the product name, e.g. ‘6.84m² roll’. Thicker rolls are shorter, so they cover less floor per roll.
  • Area needed = loft area × layers, plus the waste allowance.
  • Rolls = area needed ÷ coverage per roll, rounded up to whole rolls.
  • Prices are live from the shop, ex VAT, with VAT at 20% shown for the total.

Questions

How thick should loft insulation be?

Current UK guidance for a loft insulated at the joists is around 270mm of mineral wool in total. That’s commonly done as a layer between the joists plus a second layer laid across them. Check the joist depth in your loft and what your building control body needs if it’s part of building work.

Do I deduct the joists?

No. Rolls are laid between the joists and the offcuts fill the ends, so using the full floor area plus waste is a sensible estimate.

Which thickness goes between the joists?

Choose a roll no thicker than your joists are deep for the first layer, so the top layer can be laid across them. Then make up the rest with the cross layer.

Can I use rolls in a loft I want to board for storage?

Squashing mineral wool under boards reduces how well it works. If you need storage, keep the insulation below the boards at full thickness by raising the deck, or ask us about rigid PIR boards with our insulation calculator.

Is there a minimum order?

Yes. Insulation has a £400 ex VAT minimum order, with free delivery to mainland England. Call us on 03330 908479 for smaller orders and we’ll see if we can help.