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Home & garden.

30 June 2021

Installing sheet insulation

Sheet insulation works well in a loft conversion, as it’s a good alternative to insulating the floor. Find out how it works and how you can fit sheet insulation.
Which?Editorial team
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Wondering if you should install sheet insulation? We tell you what sort of loft sheet insulation’s suitable for, plus what you need to do before installing it.

If you’re planning a loft conversion or already use your loft as an extra room, insulating the sloping surfaces of your roof using sheet insulation can be a good alternative option to insulating the floor. 

But you should expect to pay more for this type of material than other types of loft insulation.

Fitting sheet insulation

This type of insulation is fixed between the roof rafters, rather than between joists. And like blanket insulation, sheet insulation can be cut to fit or bought in precut packs.

To avoid condensation, always leave sufficient space between the insulation and roof slates or tiles to allow for ventilation. It’s also important to check that your roof has no leaks or weaknesses that could let in damp before you start the work.

If the width of your roof rafters is too thin for sheet insulation, you could consider using foiled quilt insulation instead.

Sheet insulation can be covered with plasterboard once laid to give a clean finish.

Before installing insulation

Whatever type of insulation you choose, you’ll need to make a few preparations before you start. If you’re not sure what insulation will suit your loft best, consult a professional.

Clearing your loft

Even if you’re getting a professional loft insulation installer to complete the work for you, you’ll usually need to clear your loft before they arrive.


Wiring needs to be dealt with safely. Wires should be kept above the insulation but not stretched if they don’t comfortably reach. An electrician will be able to reroute any problematic wiring. You can use our Which? Trusted Traders service to find a recommended electrician near you.

Pipes and tanks

Pipework and tanks in the loft should also be insulated correctly, as less heat will be escaping into the loft and protecting pipes from freezing.

If in doubt

Insulation must be installed following the manufacturer’s instructions to achieve the full benefit. If you're unsure about any aspect of insulating your loft, you should contact a professional insulation fitter.

If you’re researching sheet insulation because you’re thinking of getting a loft conversion, then you need to read our expert guide on loft conversion costs.