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Home & garden.

23 July 2021

Solid wall insulation costs and savings

Find out how much solid internal and external wall insulation costs, the amount of energy it saves, and whether solid wall insulation is right for your home.
Which?Editorial team
Buildingsolidwall2 450380

If your home has solid walls, you could save between £115 and £360 a year by installing solid wall insulation.

About a third of UK homes have solid walls, according to the National Insulation Association. It estimates that 45% of the heat from these homes could be escaping through walls.

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How much does external solid wall insulation cost? 

We've worked with the Royal Institution of Chartered Surveyors*, which publishes average building work and repair costs, to bring you the average cost for external solid wall insulation. 

We've also split these so you can look at the average costs for a terraced, semi-detached and detached house. Do bear in mind that costs will vary, depending on where you live in the country. 

Only logged-in Which? members can view our recommendations in the table below. If you're not yet a member, join Which? to get instant access.

House type
Price from
Price to
Table notes: This includes, 100mm expanded polystyrene insulation (EPS) board to external brick wall, prime and render.

Solid wall insulation savings 

How much money solid wall insulation will save you each year will depend on the type and size of your home.

The chart below show the average reductions to heating bills and CO2 emissions for homes of differing sizes.

Solid wall insulation

Remember that the price you'll pay for external wall insulation will be affected by the condition of your walls and whether other building work or repairs will be taking place at the same time, as well as your property size. 

Solid wall insulation is more expensive than cavity wall insulation, but it should lead to bigger savings on heating bills. 

The type you need is determined by what type of walls you've got. Head to our guide to cavity wall insulation to find out more.

Internal or external wall insulation

Solid wall insulation can be applied to either the inside or outside of solid walls. A professional installer should be able to advise you on which option is most suitable for your home.

Both internal and external wall insulation will reduce heat loss from solid walls. The type you choose will be based on factors including:

  • your budget
  • ease of access
  • aesthetic considerations
  • the severity of heat loss from your property
  • whether your home requires other repair work to interior or external walls.

External solid wall insulation

External solid wall insulation is usually installed when a building has severe heating problems or already requires some form of external repair work.

Installation involves fixing an insulating material to external walls, with a protective render and/or decorative cladding over the top, so it will affect your home's external appearance. The thickness of the insulation needs to be between 50-100mm. 

External insulation is generally more expensive than internal, though you'll avoid the significant re-decorating that comes with internal insulation. 

Once your external insulation is fitted, decorative coatings and cladding can be used to improve your home's kerb appeal. This can match a wide variety of homes, including Georgian, Victorian and Edwardian properties.

Internal solid wall insulation

Internal solid wall insulation usually involves fitting ready-made rolls or boards of insulating material to the inside walls of your house. This can be disruptive – you'll need to move plug sockets, radiators and fitted furniture, and redecorate your walls.

Your walls will need to be carefully prepared before internal wall insulation can be fitted. Any damaged plaster needs to be either repaired or removed, and bare brickwork should be treated to eliminate areas where air can escape. 

The extra thickness of insulated walls will reduce your floor space ever so slightly. 

However, this option is usually cheaper than external wall insulation and can be installed on a room-by-room basis.

Solid wall insulation subsidy

A subsidy called the Energy Company Obligation (ECO) might be available to you. Find out more in our guide to the Energy Company Obligation.

You can find out more information about solid wall insulation, including how to find an installer, from the NIA and the Insulated Render and Cladding Association websites. 

To find a local, trustworthy installer, go to Which? Trusted Traders. You can also use our Trusted Traders search tool below.

RICS cost calculations

*To arrive at the average prices above, RICS uses cost data from its Building Cost Information Service (BCIS) database, where costs are collated from a variety of sources and analysed. 

Materials costs are based on the best trade prices from a range of suppliers across the UK, which are then benchmarked to reveal the best national average. Labour rates are based on the current Building and Allied Trades Joint Industrial Council wage agreement. Data copyright RICS 2020, reproduced with permission. Data is current as of October 2020.