External & Solid Wall Insulation Grant 2026

What Is Solid Wall Insulation?

Solid wall insulation adds a layer of insulating material to walls that have no cavity — the single-skin brick, stone, or concrete walls found in around 30% of UK homes. Most properties built before the 1920s have solid walls, and without insulation they lose twice as much heat as cavity walls. That makes solid wall insulation one of the most impactful energy efficiency improvements you can make.

There are two methods: internal wall insulation (fitted inside) and external wall insulation (fitted outside). Both are covered by the ECO4 grant scheme and by the Warm Homes: Local Grant, which means qualifying households can have either type installed at no cost.

Why Solid Walls Matter

If your home was built before the 1920s, it almost certainly has solid walls. Many homes built up to the 1930s and even some post-war properties also have them. You can check by measuring the width of an external wall at a window or door opening — solid walls are typically 23cm (9 inches) or less, while cavity walls are usually wider. The brickwork tells you too: a solid wall shows shorter header bricks at intervals, where a cavity wall shows a uniform stretcher bond.

The problem with solid walls is simple: they have no air gap to slow heat transfer. A solid brick wall conducts heat roughly twice as fast as a cavity wall, meaning your boiler works harder and your bills are higher. In older stone-built homes, heat loss can be even greater. It is also why solid-walled homes cluster at the bottom of the EPC bands — and why they are exactly the properties the grant schemes are aimed at.

External wall insulation grants

External wall insulation (EWI) fixes rigid insulation boards to the outside of your walls and covers them with a protective render or cladding system. The result is a fresh, weather-resistant exterior finish and a warmer home inside. It is the option grant schemes prefer where the property allows it, because it works better per pound spent.

• Expanded polystyrene (EPS) — the most common choice, lightweight and cost-effective
• Mineral wool boards — fire-resistant and breathable, good for older buildings
• Phenolic or PIR boards — thinner for the same insulation value, but more expensive

External insulation is more effective overall because it wraps the entire building envelope, eliminates cold bridges at floor and ceiling junctions, and protects the existing brickwork from weathering. It does not reduce room sizes and causes minimal disruption inside. The trade-offs are that it changes the exterior appearance, it needs eaves, sills and downpipes altering to suit the new wall thickness, and it costs more than internal insulation.

Installation Process — External

1. Scaffolding erected — scaffolding is put up around the property
2. Wall preparation — existing render or loose material is removed, walls are cleaned
3. Insulation boards fixed — rigid boards are mechanically fixed and adhesive-bonded to the walls
4. Reinforcement mesh — a fibreglass mesh is embedded in a base coat over the insulation
5. Render or cladding applied — a coloured render or decorative cladding is applied as the final finish
6. Details finished — window sills, reveals, and roof edges are sealed and trimmed
7. Scaffolding removed — final inspection and scaffolding comes down

EWI is only worth doing to a whole elevation, and ideally a whole building. Insulating one wall and leaving the rest bare moves the cold spot rather than removing it, which is why grant-funded EWI is normally specified as a whole-house job.

Internal wall insulation grants

Internal wall insulation (IWI) adds insulation to the inside face of your external walls. It is the route used where EWI is impossible — a listed building, a conservation area, a terrace where the neighbours are not doing the same, or a household that simply cannot accept the change in appearance. There are two main approaches:

• Insulation boards — rigid insulation panels (typically PIR or phenolic foam) bonded directly to the wall with adhesive and mechanical fixings. This is the thinner option, losing only around 50mm of room depth.
• Stud wall with insulation — a timber or metal frame is built against the wall and filled with mineral wool or rigid insulation, then covered with plasterboard. This is more versatile for uneven walls but takes up more space (around 80-100mm).

Internal insulation is generally cheaper and does not require planning permission, making it suitable for terraced houses, flats, listed buildings, and properties where the external appearance cannot be altered. The drawbacks are losing a small amount of floor space in each room, repositioning radiators, light switches and sockets, and the risk of cold bridging at party walls, floor joists and window reveals if the detailing is rushed. Moisture management matters more with IWI than with EWI, because the masonry behind the insulation stays cold.

Installation Process — Internal

1. Survey and assessment — an installer surveys your walls, checks for damp, and measures up
2. Preparation — furniture is moved away from walls, carpets may be lifted at edges
3. Damp treatment — any existing damp issues are resolved before insulation goes on
4. Insulation fitting — boards are bonded/fixed to walls, or stud frame is built and filled
5. Plasterboard and finishing — new plasterboard is fitted and skimmed for a smooth finish
6. Reinstatement — sockets, switches, radiators, and skirting boards are repositioned

Planning permission and permitted development for external wall insulation

Cladding a house — which is what EWI is, in planning terms — is normally permitted development and does not need a planning application, provided the new materials are of a similar appearance to those used in the construction of the house. That condition is the catch: a smooth coloured render over a brick terrace is not always accepted as “similar appearance”.

Planning permission is required if your home is in a conservation area, a National Park, an Area of Outstanding Natural Beauty or the Broads. Listed buildings need listed building consent for significant works, internal or external, wherever they are. Those rules are set out by the Planning Portal, and your local planning authority can add requirements of its own, so check with your council before committing to an external system.

Separately from planning, all solid wall insulation must meet building regulations, and grant-funded work must be installed by a TrustMark-registered contractor working to the PAS 2035 retrofit standard with a retrofit coordinator overseeing the design. If planning rules out EWI, internal insulation is the fallback and is funded on the same terms.

Solid wall insulation grants: who qualifies

Three routes are live in 2026. You need to clear one, not all three.

ECO4 — to 31 December 2026

The Energy Company Obligation (ECO4) is administered by Ofgem and delivered by energy suppliers. It was extended once and now closes on 31 December 2026, with no carry-over and no ECO5 to follow. It funds both internal and external solid wall insulation for qualifying households, covering materials, labour and the associated making-good. You may qualify if someone in the home receives one of the qualifying benefits:

• Universal Credit
• Pension Credit (Guarantee Credit or Savings Credit)
• Income Support
• Income-based Jobseeker's Allowance (JSA)
• Income-related Employment and Support Allowance (ESA)
• Housing Benefit
• Child Benefit, within the scheme's household income thresholds
• PIP, DLA or Attendance Allowance do not qualify on their own — a means-tested benefit in the household or an LA Flex route is also needed

Child Tax Credit and Working Tax Credit were on this list for years and you will still see them quoted elsewhere. Tax credits ended on 5 April 2025 and claimants were moved to Universal Credit or Pension Credit, so it is the replacement benefit you now claim on.

Your home must also have an EPC rating of D or below and have solid walls. Most pre-1920s properties meet both criteria. Check your eligibility now, or read our guide to EPC ratings and ECO4.

Warm Homes: Local Grant — England, to March 2028

The Warm Homes: Local Grant is a £500m programme delivered by councils and the installers they appoint. It funds measures in full and does not require a benefit claim: one of three routes must apply — gross household income under £36,000, someone in the home on one of six listed benefits, or a postcode among the most income-deprived in England. The home must be EPC D to G and owner-occupied or privately rented with the landlord's consent (F and G rentals need a registered MEES exemption). Social housing is not eligible; park homes are. Not every council joined, so availability is postcode by postcode.

LA Flex — no benefits needed

LA Flex lets your council declare you eligible for ECO4 on its own criteria — usually low income or vulnerability to cold — without any benefit claim. It sits inside ECO4, so it ends when ECO4 does.

Scotland and Wales

ECO4 applies across Great Britain, so Scottish and Welsh households on qualifying benefits can be funded through it. The Warm Homes: Local Grant is England only. Scotland's route is Warmer Homes Scotland via Home Energy Scotland; Wales has the Warm Homes Nest scheme. Solid wall work is common in both, because so much of the pre-1919 stock is there.

Why the £16,600 Warm Homes cap matters for solid walls

The Warm Homes: Local Grant has two spend caps: £16,600 for energy-performance measures (insulation, doors, windows, ventilation) and a separate £16,600 for low-carbon heating. The important detail is that the cap is averaged across a council's project, not applied rigidly to every house. One property can go over if others come in under.

For most measures that cap is irrelevant — loft insulation costs a few hundred pounds. For solid wall insulation it is the whole game. A full external wrap on a three-bedroom semi can absorb most or all of the energy-performance allowance on its own, which is why councils tend to fund EWI selectively: on the worst-performing properties, in street-level schemes where several neighbouring homes are done together, or where internal insulation would not deliver enough improvement.

What this means in practice: if your home is a good candidate, say so early and be prepared to wait for a scheme in your area rather than an individual install. And if you are quoted a “contribution” towards a Warm Homes measure, be careful — the programme is designed to fund measures in full for eligible households.

What it costs and what the grant covers

Paying privately, internal wall insulation runs to roughly £4,000–£13,000 and external wall insulation to £6,000–£15,000, depending on the size of the house, the number of exposed elevations and how much preparation the walls need. Those are the figures a grant is displacing, and they are why solid wall insulation is rarely done on a household's own money.

Where a grant applies, it covers the insulation system itself, the labour, the scaffolding, the render or plasterboard finish and the reinstatement of sills, sockets and radiators. What it does not cover is unrelated repair work — a failing roof, defective gutters, structural cracking or rising damp all have to be put right first, at your cost, before an installer will insulate over them. Ask about that at the survey, not after.

Disruption and how long it takes

External: two to four weeks for a typical semi-detached house, with scaffolding up for most of it. You stay in the house throughout. Work is weather-dependent, so installers prefer spring to autumn, and a wet fortnight can add a week. Inside, the disruption is limited to the days when window reveals are made good.

Internal: one to two weeks per room, and it is genuinely disruptive — rooms are emptied of furniture along the insulated walls, there is plaster dust, and radiators and sockets come off and go back. Most households do it room by room rather than all at once. Redecoration afterwards is on you.

Before either starts there is a retrofit assessment of the whole house under PAS 2035, and after both there is a sign-off and lodgement with TrustMark. Budget several weeks between your first eligibility check and the first day on site.

How Much Can You Save?

Solid wall insulation delivers some of the biggest energy savings of any home improvement. According to the Energy Saving Trust, typical annual savings are:

• Detached house: £375 – £475/year
• Semi-detached house: £255 – £350/year
• Mid-terrace house: £225 – £295/year
• Bungalow: £200 – £280/year

Over a 25-year lifespan (typical for solid wall insulation), that is £5,625 to £11,875 in total savings — and you do not pay for the work if you qualify through ECO4 or the Warm Homes: Local Grant. The comfort difference is usually more noticeable than the bill difference: cold external walls stop radiating, draughts at skirting level drop, and rooms hold heat for hours longer.

GBIS — a Former Route to Free Insulation (Now Closed)

The Great British Insulation Scheme (GBIS) offered a second pathway to free solid wall insulation. If your home was in council tax band energy grants A-D, you could qualify regardless of your income or benefits. The GOV.UK referral service for GBIS closed on 31 March 2026. If you do not qualify for ECO4 (which runs to 31 December 2026), check the LA Flex scheme and the Warm Homes: Local Grant instead — the council-run routes that can qualify you without benefits now that the GBIS referral route has closed. See ECO4 vs GBIS for how the two compared.

How to apply

1. Check the routes in one pass. Use the eligibility checker, which covers ECO4, LA Flex and the Warm Homes: Local Grant. In England you can also apply directly through the government's checker on GOV.UK, and the council must contact you within 10 working days.
2. Gather evidence. Benefit award letters or proof of household income, your EPC, and — if you rent — written landlord consent.
3. Retrofit assessment. An assessor surveys the whole house and a retrofit coordinator designs the package. Solid wall insulation is usually specified alongside loft or room-in-roof insulation and ventilation improvements, because insulating walls alone can trap moisture.
4. Planning check. For EWI, confirm permitted development or apply for permission.
5. Install and sign-off. Work is lodged with TrustMark and a new EPC usually follows.