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Updated: 11 Mar 2022

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

About a third of UK homes have solid walls, according to the National Insulation Association (NIA) — and an estimated 45% of the heat from these homes could be escaping through walls.

Trying to save money on your energy bills? Use our independent switching site, Which? Switch, to find a cheaper energy tariff.

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 split it so you can look at the average costs for a terraced, semi-detached and detached house. 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 typePrice fromPrice to
Table notes: This includes 100mm expanded polystyrene insulation (EPS) board to external brick wall, prime and render.

Solid wall insulation savings 

The amount of money you'll save annually with solid wall insulation will depend on the type and size of your home.

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

Solid wall insulation

Savings per yearCO2 savings per year
Detached house (four bedrooms)£4151840kg
Semi-detached house (three bedrooms)£2451090kg
Mid-terrace house (three bedrooms) £155670kg
Detached bungalow (two bedrooms)£165740kg
Mid-floor flat (two bedrooms)£115510kg

Figures based on a typical gas-heated home in England, Scotland and Wales. All data obtained from the Energy Savings Trust (EST).

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 the size of your property. 

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

The type of insulation you need is determined by the type of walls you have. 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 50-100mm. 

External insulation is generally more expensive than internal, although you'll avoid the significant redecorating that comes with internal insulation. 

Once your external insulation is fitted, you can use decorative coatings and cladding 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. 

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

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 2021, reproduced with permission. Data is current as of October 2021. 

Find the answers to your solid wall insulation questions:

What type of walls does my property have?

If your home was built any time from 1920 onwards, it's likely to have cavity walls. The cavity should be at least 50mm wide and the walls need to be in good condition to be suitable for cavity wall insulation

If your home was built in the past 20 years, it's likely that the cavity walls have already been insulated.

If your home is more than 100 years old, it's likely to have solid walls. That means you'll need solid wall insulation to stop heat from escaping.

Can I get financial help for solid wall insulation?

There is little financial help available to help you pay for solid wall insulation. Contact your council's energy efficiency officer to find out if something might be available in your area. Certain households might qualify for the Energy Company Obligation.

Do I need planning permission for solid wall insulation?

Planning permission is not normally required for wall insulation.

However, if your property is listed, is in a conservation area or if the insulation will change the appearance of your property, you should consult your local planning authority.

Where can I find a solid wall insulation installer?

Make sure you choose an installer registered with one of the following organisations:

  • National Insulation Association (NIA)
  • British Board of Agrément (BBA).

Also check that your installer has signed up to a code of conduct, such as the NIA's Code of Professional Practice. 

To find a local trustworthy installer, go to Which? Trusted Traders

You can also contact Simple Energy Advice with any questions by calling 0800 444202.

What other types of insulation are available?

Insulating your loftdoesn't cost much and could save households up to £215 a year.

You can buy jackets to fit around your hot water cylinder and piping. These are available from DIY stores and you can fit them yourself, as long as your pipes are easily accessible.

The energy savings are smaller than with wall or loft insulation but, as jackets cost around £15, they pay for themselves in a year or less.

You can also reduce the amount of heat lost in your home by fitting draught excluders around doors, windows and letterboxes. Gaps between skirting boards and floorboards are also worth tackling.

Double glazing also cuts heat loss and reduces noise and condensation problems. You can expect savings of up to £115 a year on bills if you replace single glazing with double glazing throughout your house. Remember to close your curtains at dusk to stop heat escaping. 

To reduce your fuel bills further, make sure you're on the right energy tariff. Use our independent switching site, Which? Switch, to compare gas and electricity prices.