Cavity Wall Insulation Grant

Free cavity wall insulation — what it is and why it pays

A cavity wall is two separate leaves of masonry — usually brick outside and brick or block inside — with a gap of roughly 50mm to 100mm between them. The gap was originally there to stop rain crossing from the outer leaf to the inner leaf. It also lets air circulate, which carries heat straight out of the building.

Cavity wall insulation fills that gap with a material that traps still air. Three fills are common:

• Blown mineral wool — loose fibres blown in under pressure. The most widely used full-fill material.
• Polystyrene beads — small beads carried in a binder that sets lightly, so the fill stays put and water is less able to track across. Often specified for more exposed walls.
• Urea-formaldehyde foam — injected as a foam that cures in the cavity. Older, less common in new grant work.

Whichever material is used, the aim is the same: stop the convective loop inside the wall. The Energy Saving Trust puts the resulting saving at up to £380 a year for a detached house.

How much does cavity wall insulation save?

Energy Saving Trust figures for a typical gas-heated home in Great Britain (fuel prices as of July 2026):

• Detached house: up to £380/year
• Semi-detached: up to £200/year
• Mid-terrace: up to £110/year
• Detached bungalow: up to £160/year

These savings add up to thousands over the life of the insulation, which lasts 25+ years with no maintenance. The saving is larger the more exposed wall your home has, which is why a detached house gains more than three times what a mid-terrace does.

What if you are not eligible for a grant? Paying privately, cavity wall insulation typically costs £1,500–£3,000 depending on property size and access (the Energy Saving Trust's typical figure is about £2,200) — and with savings of up to £380 a year, the Energy Saving Trust says it usually pays for itself in five years or less. It is also one of the few measures where a paid install is genuinely affordable, unlike solid wall work.

Does my home have cavity walls?

Most homes built between 1920 and 1990 have cavity walls. Before the 1920s, walls were generally solid — if that is your house, you want solid wall insulation instead. Three quick checks:

• Brick pattern. If every visible brick is the same length (a stretcher bond), the wall is almost certainly a cavity wall. If shorter bricks appear at regular intervals — header bricks, laid end-on to tie the wall together — it is probably solid.
• Wall thickness. Measure at a window or door reveal. A cavity wall is normally 270mm or more; a solid brick wall is around 230mm.
• Your EPC. The certificate states the wall type and whether it records the cavity as filled or unfilled. You can look yours up on the government's EPC register.

Homes built from the mid-1990s onwards were usually insulated at the point of construction, so there is nothing to fill. Grants are aimed at unfilled cavities — typically 1920s to early-1990s housing that was never done, or was done badly.

Is my home suitable for cavity wall insulation?

A survey is required either way. Before any grant work goes ahead, an installer inspects the wall — usually with a borescope through a small hole — to confirm the cavity is clear, dry and wide enough to fill. Homes with damp problems, very exposed weather-facing walls, or cavities that are too narrow or already partly filled may not be suitable. The survey exists to catch this before installation, and it is normal for a proportion of surveyed homes to be turned down.

Exposure to wind-driven rain

The main reason a technically sound cavity gets refused is exposure. Surveyors assess the wall against BS 8208, the British Standard for judging whether an existing cavity wall can be filled, which maps the UK by exposure to wind-driven rain. On a severely exposed wall — coastal, high ground, or a west-facing elevation with nothing in front of it — a full-fill material can give rain a path across the cavity to the inner leaf. In those locations an installer may specify bonded beads rather than mineral wool, insist the outer leaf is rendered or repointed first, or decline the job.

Damp, defects and when the fill has to come out

Cavity wall insulation does not cause damp in a sound wall. It causes problems where the wall was already defective: cracked render, failed pointing, a bridged or blocked cavity, missing cavity trays above openings, or rubble left in the gap by the original builder. Any of those must be fixed before a fill goes in, and a good surveyor will say so.

Where an older fill has slumped, become saturated or was installed in an unsuitable wall, the remedy is extraction — the fill is physically vacuumed out through drilled holes, the cavity is dried and inspected, and the wall is either left clear or re-filled with a suitable material. Extraction is specialist work, and it is not the same job as a fresh install. If your existing insulation was fitted under a government scheme and has failed, start with the installer's guarantee rather than a new grant application.

The CIGA guarantee

Grant-funded cavity wall insulation is normally covered by a 25-year CIGA guarantee (Cavity Insulation Guarantee Agency), which covers the insulation material and the workmanship. Grant work also has to be carried out by a TrustMark-registered installer working to the PAS 2035 retrofit standard, which is what puts a qualified assessor and a retrofit coordinator between you and a bad install. Keep the guarantee paperwork — it is what you rely on if the fill fails years later.

How cavity wall insulation is installed

1. Small 22mm holes drilled in external mortar joints, usually in a grid pattern across the wall
2. Insulation material (mineral wool, polystyrene beads, or foam) injected into the cavity
3. Airbricks, flues and vents are sleeved or protected so they are not blocked
4. Holes sealed and colour-matched to your mortar
5. Takes 2-3 hours — no internal disruption

Nothing needs to come off the walls inside, no floors are lifted and you do not have to move out. On a grant job the installer also lodges the work with TrustMark and issues the CIGA guarantee, which is what makes it traceable afterwards.

Cavity wall insulation grants: who qualifies in 2026

There are three live routes, and they test different things. You only need to clear one of them.

Route 1 — ECO4, if someone in the home claims a qualifying benefit

ECO4 is means-tested through the benefits system. The qualifying benefits include Universal Credit, Pension Credit (Guarantee or Savings Credit), Income Support, income-based Jobseeker's Allowance, income-related Employment and Support Allowance, Housing Benefit and Child Benefit within the scheme's income thresholds. On top of the benefit, the property normally has to be rated EPC D or below (privately rented homes generally need to be EPC E or below). Owner-occupiers and private tenants can both apply; private tenants need the landlord's written consent. Our guide to ECO4 eligibility sets out the full list.

Route 2 — Warm Homes: Local Grant, no benefits needed (England)

The Warm Homes: Local Grant does not require a benefit claim at all. One of three tests must be met: gross household income of £36,000 a year or less; someone in the home receiving one of six listed benefits; or a home in a postcode among the most income-deprived in England. The property has to be EPC D to G, and it must be owner-occupied or privately rented with the landlord's agreement. Privately rented homes rated F or G need a registered MEES exemption. Social housing is not eligible, and park homes are. Councils usually contact an eligible household within 10 working days of a referral.

Route 3 — LA Flex, if your council runs it

LA Flex lets a council declare you eligible for ECO4 on its own published criteria — typically an income ceiling, a health condition made worse by a cold home, or a referral from a health or support service. No benefit claim is needed. The criteria are set locally and change, so the only reliable answer comes from your own council's statement of intent.

Landlords and tenants

Private landlords can have cavity wall insulation funded on a let property under ECO4 and, in England, under the Warm Homes: Local Grant — the tenant's circumstances are what qualify the property, and the landlord must consent in writing. See energy grants for landlords. Park home residents have their own route; see park home insulation grants.

Government grants for cavity wall insulation: which scheme is it now?

If you have searched for a “free cavity wall insulation government scheme” you have probably landed on pages about the Great British Insulation Scheme. That scheme is closed. Here is the honest picture in September 2026, scheme by scheme.

ECO4 — the supplier-funded route, open until 31 December 2026

The Energy Company Obligation is a legal obligation on larger energy suppliers, administered by Ofgem. Its fourth phase, ECO4, was extended once and now closes on 31 December 2026. The extension exists so suppliers can finish existing targets and put right faulty installations — there are no new targets, no carry-over into a later phase and no ECO5. Eligible households are still being installed now, but the window is closing, and cavity wall work has to be surveyed, approved and completed before the deadline.

Warm Homes: Local Grant — the England replacement, to March 2028

The Warm Homes: Local Grant is a £500m programme running from April 2025 to March 2028. It is delivered by councils and the installers they appoint, not on the open market, and it funds measures in full for eligible households in England. Cavity wall insulation is squarely the kind of fabric measure it is designed to pay for, because it is cheap per unit of heat saved. Your home must be rated EPC D to G, and one of three routes must apply: household income of £36,000 a year or less before tax; someone in the home receiving Universal Credit, Pension Credit, Housing Benefit, Income Support, income-based Jobseeker's Allowance or income-related Employment and Support Allowance; or a postcode in the most income-deprived 20% of England.

LA Flex — the council declaration route

LA Flex (formally ECO4 Flex) lets a council declare a household eligible for ECO4 on its own criteria, usually low income or vulnerability to cold, without any benefit claim. It is useful precisely because it catches people the benefit test misses — but it sits inside ECO4, so it ends when ECO4 ends.

Scotland and Wales

ECO4 runs across Great Britain, so a Scottish or Welsh household on qualifying benefits can still get cavity wall insulation through it. The Warm Homes: Local Grant, however, is England only. In Scotland the equivalent is Warmer Homes Scotland, accessed through Home Energy Scotland; in Wales it is the Warm Homes Nest scheme. See our guide to energy grants in Scotland for the Scottish route.

Nobody is guaranteed a grant under any of these schemes. Funding is finite, councils joined the Warm Homes programme at different times, and every route ends with a survey that can rule your walls out.

How to apply for a cavity wall insulation grant

1. Check which route fits. Start with the eligibility checker — it covers ECO4, LA Flex and the Warm Homes: Local Grant in one pass, so you are not applying three times. In England you can also go straight to the government's own checker on GOV.UK.
2. Get your paperwork together. Benefit award letters or proof of household income, and your EPC if you have one. If you are a tenant, ask your landlord for written consent early — it is the single most common thing that stalls an application.
3. Home assessment. A retrofit assessor visits, produces the whole-house assessment that PAS 2035 requires, and confirms what the property needs. Cavity wall insulation is often recommended alongside loft insulation because doing both together is cheaper per household.
4. Wall survey. The borescope check described above. This is where suitability is confirmed or refused.
5. Installation and sign-off. Two to three hours of work, then the guarantee and TrustMark lodgement, and usually a new EPC reflecting the improvement.

Check Current Routes

Check your eligibility in 60 seconds for ECO4, LA Flex, Warm Homes and current supplier-led insulation routes.