Last updated: 11 September 2026
Complete guide to cavity wall, loft, solid wall and floor insulation: how each one works, what it costs, what it saves, and which government scheme pays for it if you qualify.
This page is the explainer: what each type of insulation actually is, what it costs and what it saves. If what you want is funding, start with our insulation grants hub, which sets out every scheme open in 2026 and who qualifies for each.
Prevents heat rising through roof. Easiest to install DIY. Recommended depth 270mm.
Fills gap in walls built 1930s-1980s. Professional installation only. Quick 1-day job.
Internal or external insulation for pre-1930s homes. Higher cost but excellent results.
Suspended floors & solid floors. Prevents heat loss through ground. Often overlooked.
Loft insulation is the most cost-effective home improvement you can make. Heat rises, and without adequate loft insulation, up to 25% of your home's heat can escape through the roof.
Current building regulations recommend 270mm depth of mineral wool insulation. Many homes have insufficient insulation:
DIY loft insulation costs £200-400 for materials vs £400-600 professionally installed. DIY is feasible if you have easy loft access and no electrical complications. Professional installation is recommended for complex lofts or if claiming government grants.
Cavity wall insulation fills the gap between the inner and outer walls of your home with insulating material, preventing heat loss through the walls.
Houses built between the 1930s and 1980s typically have cavity walls. Here's how to check:
Professional cavity wall insulation takes just 1-2 days:
Many homes had cavity wall insulation installed in the 1980s-2000s. Check for small filled holes in the mortar or contact your local authority for records. If you're unsure, an installer can check with a borescope camera.
Cavity wall insulation should last 25+ years and typically pays for itself within 2-5 years through reduced heating bills. Find out if cavity wall insulation is free for your property.
Solid wall insulation is for homes built before the 1930s that don't have cavity walls. It's more expensive than cavity insulation but can provide excellent energy savings.
External wall insulation may need planning permission, especially for listed buildings or conservation areas. It can also affect boundary distances. Check with your local planning authority before proceeding.
Solid wall insulation is a significant investment but can transform the comfort and energy efficiency of older homes, often saving £400+ per year.
| Insulation Type | Professional Cost | DIY Cost | Annual Saving | Payback Period |
|---|---|---|---|---|
| Loft Insulation (270mm) | £400 - £600 | £200 - £400 | £590/year | 1-2 years |
| Cavity Wall Insulation | £900 - £1,500 | Professional only | £395/year | 2-4 years |
| Internal Solid Wall | £5,000 - £8,000 | £2,000 - £3,000 | £445/year | 5-10 years |
| External Solid Wall | £8,000 - £15,000 | Not recommended | £445/year | 8-15 years |
| Floor Insulation | £800 - £1,500 | £300 - £600 | £70/year | 4-8 years |
Savings figures are based on a typical 3-bedroom semi-detached house. Actual savings depend on your home size, current heating costs, and existing insulation levels.
If you're eligible for fully funded insulation under ECO4 or the Warm Homes: Local Grant, it's worth taking, because the payback is immediate. Check your eligibility with Great British Energy to see which grants you qualify for.
Good insulation is essential if you're considering a heat pump. Heat pumps work most efficiently in well-insulated homes. Many heat pump installers require certain insulation standards before installation. Learn more about heat pump costs and whether they're worth the investment.
Knowing which type of insulation your home needs is half the job. The other half is working out who pays for it, and that depends on the measure as much as on your circumstances — the eligibility rules, the funding caps and the survey requirements all differ by measure.
In short: ECO4 runs to 31 December 2026 for households on qualifying benefits in EPC D to G homes. The Warm Homes: Local Grant runs to March 2028 in England and qualifies households on gross income under £36,000, on one of six listed benefits, or on a postcode in the most income-deprived fifth of the country. LA Flex lets a council qualify a household without benefits for as long as ECO4 lasts. The Great British Insulation Scheme closed to new applications on 31 March 2026. In Scotland the route is Warmer Homes Scotland through Home Energy Scotland; in Wales it is the Welsh Government's Nest scheme.
Top-ups and full installs between and over the joists.
Cavity wall insulation grantBead or mineral wool blown into the gap in walls built from the 1930s on.
Solid wall insulation grantInternal or external systems for pre-1930s homes with no cavity.
Underfloor insulation grantInsulation between the joists of a suspended timber floor.
Room-in-roof insulation grantFor converted lofts, where ordinary loft insulation does not apply.
Park home insulation grantPark and mobile homes have their own route and qualify for Warm Homes.
Funded work has to be carried out by a TrustMark-registered installer working to the PAS 2035:2023 standard, and for the main schemes the home has to be rated EPC D to G, so a property already rated EPC C or above falls outside them. Nobody is guaranteed funding, and you should never be asked for a deposit for grant-funded work. The full picture, scheme by scheme, is on our free insulation grants hub; if you would rather be told the answer, the eligibility checker covers every route above in one pass.
Common questions about insulation types, costs, installation and government schemes.
See if you qualify for free insulation under ECO4 or LA Flex. Enter your postcode to start.