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Cavity Wall Insulation
Cavity Wall Insulation
Walls can account for about a third of the heat lost from an uninsulated home. Find out whether your walls are suitable and find a specialist to assess them.
Understand your options
What is cavity wall insulation?
Many homes built after the 1920s have cavity walls: two layers of masonry with a gap between them. Cavity wall insulation fills that gap, usually by injecting material such as polystyrene beads through small holes drilled in the outside wall, which are then filled. The Energy Saving Trust says about 33% of the heat lost from an uninsulated home escapes through the walls.
Is it right for your home?
It suits many homes, but not all. The Energy Saving Trust advises against it where walls are exposed to driving rain or extreme weather, where there is a flood risk, where the brickwork is in poor condition, or where the cavity is narrower than 50mm. Repairs to brickwork, pointing, roofs and gutters should be done first. A survey before any work is essential.
Typical costs and guarantees
The Energy Saving Trust puts the cost for a typical home in Great Britain at around £2,200, and says the energy savings will likely pay that back in five years or less. It also says the work should come with a 25-year guarantee from the Cavity Insulation Guarantee Agency (CIGA) or an independent insurance-backed guarantee, so ask your installer which you will receive.
These are typical figures, not prices for your home. Last reviewed September 2026. Source: Energy Saving Trust, cavity wall insulation (updated May 2026).
Tell us about your project and we will pass it to Better Home Hub, which looks for a specialist who covers your area. The specialist surveys your walls and provides the quote.
From enquiry to installation
Your next steps, made clear.
Arrange a survey
A specialist checks the wall type, cavity width, the condition of the brickwork and exposure to weather before recommending anything.
Review your quote
Ask for a written quote naming the material, any repairs needed first, how the holes will be made good and the guarantee provided.
Keep your paperwork
Keep the guarantee certificate and any building control records. You may need them if you sell your home or a problem appears later.
How do I know if my home has cavity walls?
If your home was built after the 1920s, it probably has cavity walls. On exposed brickwork, cavity walls usually show an even pattern with every brick laid lengthways. A brick wall between about 260mm and 350mm thick is likely to be a cavity wall. If your walls are rendered or clad, ask a specialist.
Are my walls already insulated?
Homes built from the 1990s onwards usually have wall insulation. For older homes, an installer can do a borescope check through a small hole, your council's building control team may have records, and your energy performance certificate (EPC) may show it.
Will cavity wall insulation cause damp?
It should not if the wall is suitable and the work is done properly. Problems are more likely on walls exposed to driving rain, with narrow or blocked cavities, or in poor repair. That is why the survey matters.
How long does the work take?
The Energy Saving Trust says an average home with easy-to-reach walls can usually be done in about two hours. Larger homes, or homes needing a cavity barrier next to a neighbour, take longer.
Can I insulate a flat or a semi-detached house?
In a flat, the whole building is normally insulated, so you need agreement from the building owner. For a semi-detached or terraced house, the installer fits a barrier in the cavity so the insulation does not spread into your neighbour's wall.
Are there grants for cavity wall insulation?
Some households can get help, but schemes change. In England, the Warm Homes: Local Grant, run by councils until March 2028, can pay for insulation for eligible low-income households where the council has funding. The Energy Company Obligation (ECO4) runs until 31 December 2026, and the Great British Insulation Scheme ended on 31 March 2026. In Scotland, contact Home Energy Scotland; in Wales, Nest. We are not a government body and cannot tell you whether you qualify: check GOV.UK or your council.
Your next step
A warmer home.
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