Solid wall insulation Solid wall insulation costs and savings

House with solid wall insulation Installing solid wall insulation could cut your energy bills by up to £455 a year

If your home has solid walls, you could save between £145 and £455 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.

A quick and free way to save money on energy is to switch to a cheaper tariff. Use our independent switching service Which? Switch to find you the best deal.

Solid wall insulation costs and savings 

The tables below show how much you could reduce your heating bills and your CO2 emissions, and how long the insulation would take to pay for itself.

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

Solid wall insulation - external walls
Type of propertyInstallation costSavings per yearCO2 savings per year (kg)
Detached house (four bedrooms)Between £5,000
and £18,000
£4551,900
Semi-detached house (three bedrooms)£2601,100
Mid-terrace house (three bedrooms)£175720
Detached bungalow (two bedrooms)£180740
Mid-floor flat (two bedrooms)£145610

Table notes: figures based on a typical gas-heated home. All data obtained from the Energy Saving Trust (EST).

Solid wall insulation - internal walls
Type of propertyInstallation costSavings per yearCO2 savings per year (kg)
Detached house (four bedrooms)

Between £3,000
and £14,000

£4551,900
Semi-detached house (three bedrooms)£2601,100
Mid-terrace house (three bedrooms)£175720
Detached bungalow (two bedrooms)£180740
Mid-floor flat (two bedrooms)£145610

Table notes: figures based on a typical gas-heated home. All data obtained from the Energy Saving Trust (EST).

It's worth noting the tables above show averages. The price you'll pay for external insulation will be affected by the condition of the walls and whether other building work or repairs will be taking place at the same time, as well as your property size. 

While solid wall insulation is more expensive than cavity wall insulation, you should see bigger savings on your heating bills.

Wondering how you could pay for your insulation? Solid wall insulation can be funded through a scheme called the Energy Company Obligation. Find out more in our guide to the ECO.

Internal or external wall insulation

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

Both options will reduce heat loss from solid walls, so the decision is usually based on factors such as:

  • 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.
Internal-Solid-Wall-Insulation

Internal wall insulation is cheaper but you will lose a bit of internal space in your rooms

External solid wall insulation

External insulation involves fixing an insulating material to external walls with a protective render or decorative cladding over the top.

The thickness of the insulation needs to be between 50mm and 100mm. It's usually installed when a building has severe heating problems or already requires some form of repair work that provides the opportunity to add insulation.

External insulation is generally more expensive than the internal type. However, it's usually the most suitable option as the installation process does not disrupt the internal design and decoration of a home.

Decorative coatings can be used to improve the appearance of the outside of your home. External insulation can also match a wide variety of home designs, such as Georgian, Victorian and Edwardian-style properties.

Internal solid wall insulation

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

Your walls will need to be carefully prepared before internal 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. You’ll also experience a slight reduction in floor space due to the extra thickness of insulated walls. 

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

Paying for solid wall insulation

A subsidy called 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 an installer recommended by Which? members, go to Which? Local.

More on this...