What Does It Cost to Insulate a House?

To fully insulate a house your insulation system will need to cover the loft, external walls, and the ground floor. Whether installing these within a new build home or retrofitting them in an older property, we’re going to break down cost estimates for each, covering both DIY installation and professional fitting. These estimates are based on products sold through our website, or information from trusted websites like Checkatrade. In many cases you can save money by buying and installing your own insulation, helping to reduce your energy bills.

The Cost of Insulating a Loft

Loft insulation can be installed directly between the joists of a loft or the roof above it, with all new buildings requiring a minimum of 270mm insulation installed in their lofts. Insulating your loft floor will leave cold air in your loft space while insulating the roof will give you a warm loft. Pre-tax, a traditional loft roll will cost about £3.20 for 1m2 of insulation to 100mm depth. A general-purpose insulation board will cost more, at about £16 before VAT for 1m² at 100mm depth.

To have these installed by a professional will take a few hours and is likely to cost around £250 for the days' labour. Closed-cell spray foam insulation will cost around £35 per m2 for materials and will require a professional installation at around £250. Medium lofts are around 15m², allowing you to roughly estimate the costs to install 270mm of insulation, though to get a real estimate you’ll need to properly measure your loft, especially if you live in a tiny house.

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The Cost of Insulating Walls

For the walls of your home, you’ll be looking at three options, cavity wall insulation, internal wall insulation, and external wall insulation.

Cavity Wall Insulation 

For cavity wall insulation within an existing property, the job must be undertaken by a professional. The insulation options come at differing price tags, with mineral wool the most cost-effective. The costs of blown-in mineral wool will be about £13-£18 per m², expanded polystyrene beads will be roughly £18-£22 m², and polyurethane foam will cost roughly £23-£26 per m².

You will need to factor labour into this cost, with the job taking a couple of hours. The cost of cavity wall insulation will therefore be in the region of £475 for a standard semi-detached house, rising for the costlier materials. If you can safely insulate your cavities, then the cost to insulate a house will be considerably lower than houses that require internal wall or external wall insulation.

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Internal Wall Insulation 

Internal wall insulation can be accomplished by a skilled DIYer, with options to dot and dab insulation-backed plasterboards, or to build a batten wall with fibreglass batts or PIR boards inside. A 100mm insulation-backed plasterboard will cost about £37 per m2 before VAT. A stud wall alone is likely to cost more than this, around £55 per square metre, with 120mm insulation boards costing around £20.60 per m2 before VAT, and 120mm of slab insulation costing roughly £13.70 per m2 before VAT. For a professional installation on a 3-bedroom semi-detached house, Energy Saving Trust estimates a cost of around £10,000, which will change if you live in a larger detached house or a tiny house.

External Wall Insulation 

External wall insulation is a job that should only be attempted by a professional due to the complexity and precision needed. Energy Saving Trust estimates the average cost of external wall insulation for a 3-bedroom, semi-detached house to be around £14,000. In certain places like conservation areas external wall insulation may be prohibited, or may require planning permission, something to take into account.

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How Much Does it Cost to Insulate a Floor?

For floor insulation you will normally have two options, installing insulation boards or batts within the joists of a suspended timber floor, or installing solid insulation boards above a solid floor. For installing over a solid floor, a 50mm thick level of insulation board will cost around £8.90 per m² before tax. For a suspended timber floor, 140mm of mineral wool slab will cost around £14.20 per m² before tax.

When estimating the cost of insulating a floor it is worth considering that unless you have a usable crawl space you will likely need to remove all flooring, which could cost a considerable amount of money if it needs replacing. If installing over a solid floor, you may have to raise things like skirting boards and sockets, which can be a difficult process, and you will need to install a vapour barrier. Labour costs for installation are likely to be around £250 a day.

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How Much Does Double Glazing Cost?

Double glazing can be a great way to increase the thermal insulation level of your home, but it comes with a steep price tag. Double glazing will be sold as sets of windows and doors, with prices sometimes lowering for larger numbers, or for estimates that combine parts and fitting. For an average new uPVC double-glazed window, you will be looking at a cost of around £360. This is expensive compared to the cost of insulating a house but will bring heat savings and increase the value of a home. For smaller buildings like tiny houses, the lower number of windows will make this more viable.

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