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The average cost of roof
insulation is around £450
Pricing guides

How much does roof insulation cost?

Roof insulation is a smart way to help keep heat in your home and cut your energy bills, especially if you want your loft or attic to be a usable space. There are different ways you can insulate your roof depending on your particular circumstances, with different costs involved, so we’ve put together this guide to give you some examples of the kind of prices you can expect to pay.

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Pitched roof insulation costs

If you have a pitched roof, as found in the vast majority of homes, then you can either install simple loft insulation which sits atop the joists, but reduces the usability of the space (see our guide to loft insulation costs for more information), or you can add insulation directly under the pitched slope of the roof, insulating the entire loft space, known as warm-roof insulation. 

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In order to insulate the roof, there is a range of materials that can be added between the rafters, ensuring that adequate ventilation is left behind the insulation to help counter excess moisture that could damage the rafters. Materials that are commonly used include polystyrene insulation panels, often backed with foil, which are cut to size; mineral or fibreglass lagging, held in place with wooden slats; or expanded polystyrene products which unfurl to fill the space. Spray foam can also be used in some circumstances.

The average cost of insulation panels, the most common roof insulation, is about £25 per square metre, while spray foam insulation is at least £30 per square metre, so we would estimate that the average cost of roof insulation in a property would be about £400 to £500.

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Flat roof insulation costs

If you have areas of flat roof you wish to insulate, there are again a number of different methods you can use depending on the circumstances. Warm deck insulation is put above the deck of the roof itself and below the weather-proof layer, while cold deck goes underneath the joists, with space for ventilation. Then there is inverted roof insulation, where the insulation goes above the weather-proof layer, with a new layer, such as gravel, becoming the external face of the roof. Warm or cold deck insulation can cost around £35 per square metre, not too dissimilar from other roof insulation prices, however, exterior insulation is more expensive, and can cost around £80 per square metre. 

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