Solid Wall Insulation 2026: Grants, Costs & Savings
Solid wall insulation costs £8,000 to £22,000 in 2026. See which grants pay, how much you'll save, and check eligibility in 2 minutes.
Insulation
Loft insulation costs £300 to £600. Cavity wall is £400 to £800. ECO4 can fund both for free. Check what grants apply to your home in 60 seconds.
Grants overview
| Scheme | What you get | Who qualifies | Status | Action |
|---|---|---|---|---|
| ECO4 | Fully funded insulation | Low-income households on qualifying benefits | Ending soonuntil Dec 2026 | Check eligibility |
| Great British Insulation Scheme | Up to £1,500 off (historical) | Was D-G rated homes | ClosedMarch 2026 | Check eligibility |
| Warm Homes Local Grant | Varies by council, often covers insulation | Income <£36,000, EPC D-G, England | Open |
Reviewed against primary sources
£300–£600
Typical loft insulation cost
£400–£800
Cavity wall insulation cost
£7,500–£22,000
Solid wall insulation cost
Most insulation grants require an EPC rating of D or below, so it's the first thing to check before you apply.
ECO4 is the main route to free insulation in England, Scotland and Wales. It's funded by the big six energy suppliers (British Gas, EDF, Octopus Energy, E.ON, Scottish Power and others) who are legally required to improve the energy efficiency of the homes that need it most. If your household receives qualifying benefits, including Universal Credit, Pension Credit, Child Tax Credit or income-related ESA, and your home has an EPC rating of D or below, ECO4 can fund the full cost of loft insulation, cavity wall insulation, or solid wall insulation. Not a contribution. The whole job.
About a third of UK households meet the income criteria, which is a much larger group than most people assume. The catch? ECO4 treats your home as a whole-house project under PAS 2035, so the installer assesses everything and recommends the most effective package of measures. You don't get to cherry-pick. But the result is usually better: you might go in expecting loft insulation and come out with loft plus cavity wall plus new heating controls, all funded. The scheme is open until December 2026 according to GOV.UK, so there is still time, but the process from application to installation typically takes eight to twelve weeks. Don't leave it until November.
The Warm Homes Local Grant is newer and patchier. Delivered through local authorities with funding from the government's Warm Homes Plan, eligibility varies by council. Some areas (Sheffield and Nottingham have been particularly active) offer substantial insulation grants to households earning under £36,000 with an EPC of D or below. Others haven't set up their programmes yet. Check your local council's energy efficiency page, or run through our eligibility checker, which flags local schemes for your postcode.
The Great British Insulation Scheme (GBIS) closed on 31 March 2026. If you applied before then, your application is still being processed. If you didn't, ECO4 and the Warm Homes Local Grant are now your options.
Scotland has its own route through Home Energy Scotland, which offers interest-free loans and grants for insulation measures. If you're north of the border, start there rather than with ECO4. Welsh homeowners can access ECO4 nationally and should also check the Warm Homes Nest scheme run by the Welsh Government.
Two minutes, no phone number, no obligation. We cross-reference every active scheme.
Loft first. Always loft first.
It's the cheapest measure, the fastest to install, and heat rises, so an uninsulated loft is where you're losing the most energy. If your loft has less than 270mm of insulation (and most pre-2000 homes have 100mm or less), topping up is the single best pound-for-pound upgrade available. You'll typically recover the cost within two to three years through lower gas bills.
After loft, cavity wall. It costs more but the savings are comparable, and the installation is quick. Then floor insulation if you have a suspended timber floor. Solid wall insulation comes last because the cost is an order of magnitude higher, and the diminishing returns are real: once your loft and cavity walls are insulated, the marginal benefit of solid wall insulation is smaller per pound spent.
Honestly, this depends on your home. A 1960s cavity-wall semi with no loft insulation has a clear path: loft, walls, done. A pre-1900 solid brick terrace is a completely different project, and you should get a proper retrofit assessment before spending anything. More on that below.
If your home already has 270mm of loft insulation and filled cavity walls, adding more insulation gives diminishing returns. You're better off spending that money on draught-proofing, upgrading your heating controls, or improving your windows.
If your property is about to be demolished or is scheduled for major structural renovation, insulating now doesn't make financial sense. Same applies if you're planning a loft conversion within the next year: standard loft insulation gets ripped out during the build, so you'd be paying twice.
Spray foam insulation. Avoid it for roofs unless you've had very specific advice from a surveyor. Spray foam applied directly to the underside of roof tiles can trap moisture, damage timber rafters, and make your home harder to sell or mortgage. Several lenders now refuse properties with spray foam in the roof space. The product has its place in certain wall applications, but the roof-spray trend of 2020-2023 created real problems for homeowners. If an installer suggests spray foam for your loft, get a second opinion.
The other thing worth knowing: if you're going through ECO4 for insulation work, the installation must follow PAS 2035, the government's retrofit standard. That means a qualified retrofit assessor (often from Elmhurst Energy or a similar body) visits your home first and creates a whole-house improvement plan. It's not optional under ECO4, and it's actually a good thing: it prevents installers from doing piecemeal work that creates damp or ventilation problems down the line. If an ECO4 installer wants to skip the assessment, that's a red flag.
Our eligibility checker cross-references your home against every active insulation scheme: ECO4, the Warm Homes Local Grant, and anything available in your postcode area. It takes about two minutes and there's no phone number required, no obligation, no follow-up calls unless you ask for quotes.
You'll need your postcode and a rough idea of your property type. That's it.
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Local coverage
Insulation costs and grant availability vary by region. Enter your postcode and we'll show you which schemes are active in your area and connect you with local installers.
Common questions
Two minutes, a few questions about your home. We cross-reference every active government scheme and show you exactly what you qualify for.
| Check eligibility |
| Home Energy Scotland | Loans + grants for insulation | Scottish homeowners | Open | Check eligibility |
Fully funded insulation
Low-income households on qualifying benefits
Check eligibilityUp to £1,500 off (historical)
Was D-G rated homes
Check eligibilityVaries by council, often covers insulation
Income <£36,000, EPC D-G, England
Check eligibilityNot sure which applies to you? Check all four in 60 seconds
Last reviewed: 16 May 2026 · Next review due: 14 August 2026
£300 to £600. That's what most people pay for loft insulation, and it's the single cheapest upgrade with the biggest impact. Topping up from 100mm to the recommended 270mm of mineral wool (the standard products are Knauf and Supafil) takes a day, sometimes less, and typically saves £150 to £250 a year on heating bills according to the Energy Saving Trust.
Cavity wall insulation runs £400 to £800 for a standard three-bed semi. The installer drills small holes in the outer wall, injects insulating material (usually blown mineral wool or polystyrene beads), then patches the holes. The whole process takes half a day. If your home was built between 1920 and the mid-1990s, it almost certainly has a cavity. Pre-1920 homes are usually solid wall, which is a different conversation entirely.
That different conversation? External wall insulation costs £7,500 to £22,000. Internal wall insulation is cheaper at £5,000 to £15,000, but you lose roughly 100mm of room depth on each treated wall. Both options transform the thermal performance of a solid-walled property, and both are eligible for ECO4 funding if you qualify. For most homeowners, the decision between internal and external comes down to whether you can afford to lose the interior space or change the exterior appearance. Planning permission sometimes applies to external cladding, especially in conservation areas.
Floor insulation is the one people forget. £500 to £1,200 for a suspended timber floor. It's fiddly, the installer works from under the house if there's crawl space, but the draught reduction alone makes it worthwhile in older properties. Solid concrete floors cost more to insulate and the benefit is smaller, so the payback is longer.
Room-in-roof insulation sits at £1,500 to £3,500. If you've converted your loft into a bedroom or office, standard loft insulation doesn't apply. You need insulation between and over the rafters instead, using rigid boards like Kingspan or Celotex. It's more expensive per square metre but essential if you're heating a habitable loft space.
Flat roof insulation costs £40-£80/m² and can cut heat loss by 50%. See which grants cover it and how to get quotes. Check eligibility in 2 minutes.
Loft insulation costs £300-£600 and can cut heating bills by 25%. ECO4 funds it free for eligible homes. We cover types, thickness, grants and DIY options.
Featured guides
The cluster-level guide covering the funding scheme most households qualify for first.
GBIS closed March 2026. Find out which insulation grants are still open, what you qualify for, and how to apply. Free eligibility check in 2 minutes.
By category
Loft, cavity wall, external, internal, floor, spray foam, room-in-roof and flat roof — each with cost, install and grant routes.
INSULATION BY TYPE
Loft, cavity wall, external, internal, floor, spray foam, room-in-roof and flat roof.