Insulation calculator

How many rolls of loft insulation, or how many insulation boards, for a loft, floor or wall area, in one or more layers.

Put these calculators on your phone, free

They work like an app from your home screen, even with no signal on site. On an iPhone: tap Share, then Add to Home Screen. On Android: tap the menu (⋮), then Add to Home screen or Install app.

The free SiteHelm phone app for iPhone and Android is on its way, with the main builders' calculators in it. Tell me when it's out

Do more with SiteHelm PRO

Measure the areas off the drawing with Take-off, put the insulation on a purchase order or into your quote from the Book of rates, and save it to the job.

Free on your phone. The SiteHelm phone app for iPhone and Android is on its way, with the main builders' calculators in it, free. Tell me when it's out.

This calculator is free here on the website. The main builders' calculators are in SiteHelm PRO for your Windows PC, alongside take-off, RAMS, quotes, invoices and 40+ more tools. The first 100 get a free 1-year licence.

Get a free 1-year licence See the prices

Worked example

The first layer in a loft 8 m × 6 m, 100 mm rolls laid between the joists:

4 rolls of 100 mm loft roll

48.00 m², plus 5% = 50.40 m²
At 13.89 m² a roll

How the sum works

The area times the number of layers, plus the extra you choose, divided by the area one roll or board covers. The roll sizes in the list are typical pack figures from merchants, so check the coverage printed on the pack you buy and pick "Another product" to type it in.

Lofts

The Energy Saving Trust recommends at least 270 mm of loft insulation. It is usually laid in two layers, the first between the joists and the second across them, so work out each layer on its own. Keep the eaves clear for ventilation, don't cover light fittings that need space round them, and board walkways on raised supports rather than squashing the insulation: Energy Saving Trust: how to insulate a loft.

Walls, floors and roofs

For an extension or a new build, the thickness comes from the U-value the building regulations need, not from the area. Work the build-up out first with the U-value calculator, then use this one for the quantities.

Guides that go with it

What U-values does an extension need in England?The maximum U-values for new walls, roofs, floors, windows and doors in an extension in England, from Approved Document L Volume 1, and who checks them.How do I do a quantity take-off from drawings?How to take off quantities from drawings for a small job: scale check, set order, deductions, waste and pricing, with a worked garden room example.What should I put in a quote for building work?What a quote for building work should say: scope, exclusions, drawings, price and VAT, validity, payment stages, dates, provisional sums and variations.

More builders' calculators

Brick calculatorHow many bricks for a wall, with mortar, bags of cement and tonnes of sand. single or double skin, openings and waste.Block calculatorHow many 440 × 215 blocks for a wall (100, 140 or 215 mm), with mortar, bags of cement and tonnes of sand.Concrete calculatorM3 to order as ready-mix, or the bags of cement and tonnes of sand and gravel to mix it.Type 1, gravel and sand calculatorTonnes of mot type 1, gravel, sharp sand, ballast, scalpings or topsoil for an area and depth, with bulk bags and loads.Excavation and muck-away calculatorThe volume dug from a trench or a reduced dig, bulked up by soil type, with the tonnes, skips and grab lorry loads to take it away.Volume calculatorTanks, pits, piles, ramps and soakaways.Roof pitch and rafter calculatorPitch from the rise (or rise from the pitch), rafter length with the overhang, the stock length to buy, rafters per side and roof area.Stair calculatorNumber of risers, rise and going, pitch and the 2r + g rule, checked against approved document k for a house, utility or general stair.U-value calculatorBuild up a wall, roof or floor layer by layer and check it against part l for an extension or new home, with the insulation needed.Roof slate and batten calculatorBatten gauge, slates per m², slates to order, metres of batten and nails, from the roof area, slate size and headlap.Plaster calculatorBags of finish plaster for a skim, or hardwall or bonding and finish for float and set, from the wall and ceiling area.Tile calculatorHow many tiles and boxes for a wall or floor, with adhesive and grout, for any tile size, joint and laying pattern.Screed calculatorM3 of screed for a floor, the bags of cement and tonnes of sharp sand for a 1:4 sand and cement screed, or liquid screed to order.Patio and paving slab calculatorHow many paving slabs for an area, with the type 1 sub-base, the sand and cement for a full mortar bed, and how deep to dig.Fence panel and post calculatorFence panels and posts for a run, the post length to buy, gravel boards, and bags of postcrete from the maker's own table.Stud wall calculatorStuds, head and sole plates, noggins, sheets of plasterboard and screws for a timber stud partition, at 400 or 600 mm centres.Fall and gradient calculatorTurn 1 in 80 into a drop in mm over any length, or a drop into a gradient, with the percentage, degrees and the depth at the end.Brick and block coursing calculatorHow many brick or block courses fit a height, the nearest course heights above and below, and courses per metre.

Every calculator

The construction manager’s toolbox.

Measure from a drawing, Easy CAD, Edit PDF and Weather are free for good in your browser. Take-off, RAMS, quotes, invoices and 40+ more tools come with SiteHelm PRO.

Open SiteHelm Free See the founding offer