Cavity wall insulation cost, savings and payback

Typical UK cost of filling an unfilled cavity wall, the heating saving it can deliver, and how to check whether your walls qualify.

Most homes built after the 1920s have two masonry leaves with a gap, or cavity, between them. Injecting insulation into that gap reduces heat lost through the walls.

It is only suitable where the cavity is unfilled, wide enough and in good condition; an installer surveys the wall first.

Across the 9538 energy certificates in our dataset, 23.2% are recorded as having no wall insulation. This is an indicative figure from the certificates we hold, not a national statistic.

Typical UK cost

Item	Typical cost	Notes
Cavity wall insulation (typical semi-detached)	£1,000–£3,000	Varies with wall area and access; larger detached homes cost more.

Cost ranges are indicative and attributed to Energy Saving Trust: Insulation. Prices vary by property, region and installer – always get quotes and check the official source.

Typical saving

The Energy Saving Trust estimates cavity wall insulation can save roughly £100 to £400 a year on heating depending on the property type.

Saving figures are indicative and attributed to Energy Saving Trust: Insulation. Check the official source.

Payback

Payback is commonly within a few years for a home with unfilled cavities, though it depends on property size and how it is heated.

What affects the price

Whether the cavity is already filled (an EPC or a borescope survey shows this).
Wall area, property type and number of exposed walls.
The condition of the wall and exposure to driving rain.

Grants and funding: ECO4 and the Great British Insulation Scheme

Some households can have insulation part- or fully funded through the Energy Company Obligation (ECO4) or the Great British Insulation Scheme. Eligibility depends on income, benefits, council tax band and the home's EPC rating. See our eligibility guide and the official gov.uk pages.

Eligibility guide

Sources

This page is general information, not advice, a valuation or a survey. Figures are indicative ranges from the named public sources; check the official source before making a decision.

Related guides

See the picture in a real area

Every area page shows the local energy-band distribution and what the register estimates insulation could save.

All areas by leakiness