Cavity wall insulation grants

What cavity wall insulation is, and why it is one of the most-funded measures

Most UK homes built between roughly the 1920s and the 1990s have two layers of masonry with a gap, or cavity, between them. Insulating that gap slows the heat leaving your home through the walls. It is a quick job on a suitable property, usually completed in a few hours by injecting insulation through small holes drilled into the mortar, and at around £2,700 unsubsidised (Energy Saving Trust, 2026) it sits between cheap loft insulation and expensive solid wall work in both cost and complexity.

Because the saving-per-pound is strong on the right property, cavity wall insulation is funded across almost every current UK insulation scheme. The catch, and the honest headline of this page, is a single word: suitability. No scheme will fund a cavity fill until a survey confirms your walls actually have an unfilled cavity in good condition. That survey gates everything, and it is the reason two neighbouring houses can get very different answers.

The suitability survey: the gate that decides everything

Before any grant-funded cavity fill goes ahead, an installer carries out a suitability survey, often using a borescope to look inside the cavity. They are checking several things:

• Is there actually a cavity, and is it empty? Some walls are solid, and some cavities were filled years ago.
• Is the cavity wide enough and clear of debris or rubble?
• Is the wall in good condition and reasonably dry? Damp-prone walls, or homes in very exposed, wind-driven-rain locations, can be judged unsuitable because filling the cavity could bridge moisture across to the inner wall.
• Is the external render or pointing sound? Cracks let water in, which insulation can then hold against the inner leaf.

If the survey says no, that is not the installer being difficult, it is the survey protecting you from a fill that could cause damp. In that case, look at other measures instead: our loft insulation grants and underfloor insulation grants pages cover the usual alternatives, and homes with no usable cavity are, by definition, solid-wall properties, covered on our solid wall insulation grants page.

Failed or incorrect fills: removal and replacement

A significant number of older cavity fills have failed, slumped, or were installed in properties that were never suitable. Signs include cold patches, damp appearing on inside walls, and rising heating bills despite "insulated" walls. The remedy is cavity wall insulation extraction, cleaning out the old material, remedying any damp cause, then re-insulating only if the wall is now suitable.

This is where the schemes differ. In Northern Ireland, the Affordable Warmth Scheme can fund the removal and replacement of failed or incorrect cavity wall insulation, not just first-time fills. Elsewhere, funding for extraction is patchier and usually depends on the specific scheme and assessor, so treat replacement as something to raise explicitly with the installer and the scheme channel rather than assume. If your original fill was grant-funded and has failed, also read the quality section below, because free audits exist for some defective installs.

Which grants fund cavity wall insulation, by nation

Insulation grants are run separately in each UK nation, and mixing them up is the fastest way to be misled. Never assume a scheme from one nation applies to another. Here is where cavity wall insulation sits across the current schemes.

England: ECO4 and Warm Homes: Local Grant

ECO4 (the Energy Company Obligation, phase 4) is open and was extended to 31 December 2026. It is delivered by obligated energy suppliers, not by applying to Ofgem, and it takes a whole-house, fabric-first approach, so cavity fill is often bundled with other measures. You qualify either through a means-tested benefit or, if you are on a low income but not on benefits, through the ECO4 Flex route where your council refers you. Owner-occupiers need an EPC of D-G; private and social tenants need E-G. Full detail is on our ECO4 grant page.

The Warm Homes: Local Grant is delivered by your local council in England and runs to around 31 March 2028. It funds wall, loft and underfloor insulation among other measures. To qualify your home needs an EPC of D-G, plus one of: a household income usually at or below £36,000 a year; a qualifying means-tested benefit; or an eligible low-income postcode. Because it is council-by-council, availability genuinely varies by area.

Note that the Great British Insulation Scheme (GBIS) closed on 31 March 2026 and has no successor. If you see a site presenting GBIS as open, or promising a "new free cavity grant from April 2026", that is out of date or invented. Our ECO4 vs GBIS comparison explains the difference honestly.

Scotland: Home Energy Scotland

In Scotland the single gateway is Home Energy Scotland on 0808 808 2282. The Home Energy Scotland Grant and Loan has no benefits test but you must own and live in the home, and the measure must be recommended in an EPC or home energy report. Cavity wall insulation is capped at £2,000 under the combined per-measure caps, which broadly matches the typical cost of the job. Warmer Homes Scotland is effectively free for eligible older or vulnerable households, and Area Based Schemes are targeted by councils rather than self-applied.

Wales and Northern Ireland

Wales runs Warm Homes Nest, a Welsh Government fuel-poverty scheme covering insulation and heating; confirm current eligibility and any caps at nest.gov.wales before relying on a figure. Northern Ireland does not operate ECO4 or GBIS. Instead, the Affordable Warmth Scheme supports households with gross income under £23,000, with grants up to £7,500 (or £10,000 where solid-wall insulation is needed), and, as noted above, it can fund failed-fill removal and replacement.

What if you do not qualify for a grant?

Plenty of households fall outside the benefit and income gates. Two things still work in your favour. First, in Great Britain, installing qualifying insulation has been at 0% VAT under the Energy-Saving Materials relief, so a self-funded cavity fill is cheaper than the headline rate suggests, though you should confirm the current rate and any end date against HMRC VAT Notice 708/6, and note Northern Ireland treatment can differ. Second, the not-on-benefits routes are real: ECO4 Flex, the Warm Homes: Local Grant income and postcode routes, and the Home Energy Scotland Grant all reach households who are not claiming benefits. Our insulation grants if you are not on benefits page maps these out, and private renters should read insulation grants for private tenants, since you will usually need your landlord's permission.

Quality, standards and avoiding scams

Grant-funded work must be done to proper standards. Insist on a TrustMark-registered installer working to PAS 2035 (retrofit) and PAS 2030 (installation). A compliant job starts with a retrofit assessment and a Retrofit Coordinator, not a salesperson quoting a single measure on the doorstep. If an installer skips the assessment, treat it as a red flag.

The classic scam funnel is the "free insulation grant" cold call, text or doorstep visit. Real schemes are applied for through gov.uk, Home Energy Scotland, your council, or an accredited installer, never through an unsolicited caller. Never pay upfront and never let work start before you have written grant approval. Our insulation grant scams and is it really free pages go into detail, and you can verify any installer against the scheme channel and at trustmark.org.uk.

How to check your eligibility and apply

The honest first step is to check your EPC, because nearly every scheme is gated on a poor rating, typically D-G. Then work out which nation's schemes apply and whether you meet the benefit, income or postcode route. Our free eligibility checker walks you through this, and the grants and funding hub lists every current scheme. When you are ready, our how to apply guide explains the steps, and the cost page sets out typical prices so you can judge any quote. If you would like us to point you towards the right route, use our enquiry form or the contact page. Homeinsulationgrants.uk is an independent guide, it installs nothing and runs no grant, and applying to the real schemes through official channels is always free.

Authoritative sources

Check the official guidance before you commit:

• ECO4 on gov.uk
• Warm Homes: Local Grant on gov.uk
• Energy Saving Trust: cavity wall insulation