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Cavity Wall Insulation

Fills the gap in cavity walls to cut heat loss. Usually installed from outside, and funding may help eligible households with the cost

Funding may be available About 2 hours for an average home Save around £110-£380/year
Step 1 of 2What you need

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Tell us about the job and we’ll find up to 3 local insulation installers who cover your area and ask them to contact you with a quote. Free, no obligation.

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What is Cavity Wall Insulation?

Many UK homes built after the 1920s have cavity walls - two layers of masonry with a gap (cavity) between them. Cavity wall insulation fills this gap with insulating material, usually polystyrene beads, to slow heat escaping through your walls. In an uninsulated home, about a third of the heat lost escapes through the walls.

For an average home with easy-to-reach walls, a registered installer can usually do the job in about two hours. The Energy Saving Trust estimates it saves around £110-£380 a year depending on your home (July 2026 prices). Some households can get help with the cost through ECO4 or their council, but funding is not guaranteed.

Why Choose Cavity Wall Insulation?

Funding May Help

ECO4 (until 31 December 2026) or your council may fully or partly fund it for eligible households

Quick Install

About two hours for an average home with easy-to-reach walls

Lower Bills

Around £110-£380/year depending on home type (Energy Saving Trust)

Warmer Home

About a third of heat in an uninsulated home is lost through the walls

Little Mess

Usually injected from outside through small drilled holes

Ask for a Guarantee

Work should come with a 25-year CIGA or independent insurance-backed guarantee

How Installation Works

1

Survey

Check cavity suitability and take measurements

2

Drill Holes

Small holes drilled in the outside wall at regular intervals

3

Inject Material

Insulation blown into the cavity through the holes

4

Fill & Finish

Holes filled; the filler may not exactly match your brickwork

Cavity Wall Insulation Costs

£950-£3,900
Typical Cost (if paying)
Flat to detached house; around £2,200 for a semi
£110-£380/year
Typical Bill Savings
Around £200/year for a semi-detached house

Typical costs, last reviewed September 2026. Source: Energy Saving Trust, July 2026 prices (unsubsidised, gas-heated home).

Funding May Help With the Cost

ECO4 ends on 31 December 2026 and work must be finished by then. It is not a grant: work may be fully or partly funded, and you may be asked to contribute. In England, councils also run the Warm Homes: Local Grant (EPC D-G, household income usually £36,000 or less). The Great British Insulation Scheme closed on 31 March 2026.

UK Energy Partnership is run by Harber Glaves Trading Ltd. We are not a government body and cannot decide who gets funding. Check eligibility with the official scheme: ECO4 or Warm Homes: Local Grant.

Quick Grant Finder

Answer up to three quick questions to see which schemes may be worth checking

Is Your Home Suitable?

✓ Suitable Homes

  • Unfilled cavity walls (often homes built after the 1920s)
  • Cavity at least 50mm wide and clear of rubble
  • Brickwork in good condition
  • Not exposed to driving rain or at risk of flooding

⚠ Not Suitable

  • Solid walls (more common in homes built before 1920)
  • Already has cavity insulation
  • Narrow or uneven cavities (under 50mm)
  • Exposed sites, flood risk or unresolved damp

Solid-wall homes need external or internal wall insulation instead. Fix damaged brickwork, gutters and damp before any wall insulation.

Ready to Insulate Your Walls?

Sending an enquiry is free. Better Home Hub, which runs this site, introduces installers who may be able to help. Check they are TrustMark registered before you agree to work.

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