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Home & garden.

Installing loft insulation

Information for installing blanket, loose-fill, sheet and blown-fibre insulation in your loft, and whether or not you can fit each type yourself.
Adam Snook
Blanket2 450363

Everything you need to know about installing loft insulation, including whether you can fit it yourself.

If you're looking to insulate your loft, there are several options available. Here we look at blanket insulation, loose-fill insulation, sheet insulation and blown-fibre insulation. The advantages of each are highlighted and we'll tell you whether or not fitting each option is an easy DIY job.

Blanket insulation is the most common type of insulation and is sold in rolls, which are laid down between the flooring joists in a loft.

Loose-fill loft insulation is made from light materials, such as cork granules or even recycled newspaper, which is evenly spread in the gaps between the joists. Loose-fill insulation material comes in bags, and because you simply pour the material from the bag to lay it, it's a fairly easy task to complete yourself. Just make sure your loft is properly prepared first.

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 to insulating the floor. However, you should expect to pay more for this type of material than other types of loft insulation.

Blown-fibre insulation is made up of mineral fibres. In most cases you’ll need a professional to install blown insulation, as it needs to be blown into place with specialist equipment. Bear this in mind when you’re budgeting.

To find loft-insulation installers near you, use our Which? Trusted Traders service to find someone local to you and approved by us.

Fitting blanket insulation

Rolls of blanket insulation come in various different widths to match the size of your loft, so start by measuring the distance between joists and then buy rolls of the appropriate width.

Ideally it should fit neatly between the joists. To calculate the right amount, measure the length of the floor space to be covered. Don't stretch or tear blanket insulation – use scissors if it needs to be cut.

Unroll the insulation blanket and lay it flat between the loft joists. If possible, add a further layer of blanket insulation across both the joists and the lower layer of insulation. Be careful not to compress the insulation too much. 

If you want to use your loft for storage, you can place boards down flat and put further insulation over the top. Alternatively, you may need to raise the level of the floor to ensure that the 270mm recommended insulation is achieved. If you’re not sure of the best option, contact an installer for a professional opinion.

DIY or get a professional?

Confident DIYers should be able to lay blanket insulation relatively easily themselves – but you should always refer to the manufacturer’s instructions to ensure you’re fitting it correctly and getting the most out of your insulation.

Some insulation grants and offers are still available from energy companies. The discounted materials and installation rates on offer mean that, in some cases, getting a professional to fit your insulation could be cheaper that doing it yourself. The work may even be done free of charge.

Fitting loose-fill insulation

To fit loose-fill insulation you should first work out the floor space in square metres. You'll need approximately 200 litres of material to cover each square metre to a depth of 200mm. 

Before laying your loose-fill loft insulation, ensure the space between the joists is relatively dust-free. You should also check the depth of the joists is sufficient to hold an acceptable level of loose-fill insulation. 

The material should be poured between the joists in the roof space, ensuring there are no cracks or holes in the ceiling. Make sure you remember to brush or rake between the joists so the fill is level.

If you’re not fitting boarding over the loose-fill insulation, check the level of the material during the winter months. High winds can unsettle loose-fill insulation and blow it around your home’s roof space. 

To insulate a loft hatch, it’s best to use blanket material held in place by plastic or an old sheet. 

When is loose-fill loft insulation suitable?

Loose-fill loft insulation works well in hard-to-reach or awkwardly shaped sections. It’s also a suitable top-up material if your loft already has some insulation.

Fitting sheet insulation

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

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

If the depth of your roof rafters is insufficient for sheet insulation, you could consider using foiled quilt insulation instead. Sheet insulation can be covered with plasterboard once fitted to give it a clean finish.

Fitting blown-fibre insulation 

With this type of insulation, mineral fibres are evenly blown and spread between the joists in a loft using specialist industrial equipment. Blown-fibre insulation works well in lofts where the use of blanket insulation isn’t suitable, or if joists are obstructed. 

It’s a fairly quick job for a professional to do. Which? Trusted Traders can help you find recommended loft-insulation installers, as well as electricians and plumbers, in your area.

Before installing insulation

Whatever type of insulation you choose, you’ll need to set aside some time to do a few preparations before you start the job. If you've hired an installer, ask them if they have any particular requirements.

Clearing your loft

Even if you’re getting a professional loft insulation installer to complete the work for you, it makes sense to clear your loft before they arrive.

Wiring

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 find a recommended local electrician by visiting Which? Trusted Traders

Pipes and tanks

Pipework and tanks in the loft should also be insulated correctly. After the loft is insulated less heat will escape from rooms below, so you'll need to protect pipes to prevent them 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, contact a professional insulation fitter.

If you’re installing insulation to help cut your energy bills, you can also save money by being on the best energy deal. Use our independent switching site, Which? Switch, to make sure you’re on the cheapest energy tariff.