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Internal Wall Insulation

Insulate solid walls from the inside. Usually cheaper than external insulation, but rooms lose a little space and need redecorating

Around £12,000 for a 3-bed semi Save around £140-£500/year Check TrustMark registration
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What is Internal Wall Insulation?

Internal Wall Insulation (IWI) involves fitting rigid insulation boards, an insulated stud wall or insulating plaster to the inside of solid external walls. It suits homes where external insulation isn't possible or wanted, for example because of planning restrictions or appearance.

About a third of the heat lost from an uninsulated home escapes through the walls. The Energy Saving Trust estimates solid wall insulation saves around £140-£500 a year depending on your home (July 2026 prices). IWI is generally cheaper than external insulation and leaves the outside unchanged, but it slightly reduces room sizes, and skirting boards, door frames and fittings have to be removed and refitted.

Key Benefits

Funding May Help

ECO4 (until 31 December 2026) or your council may fully or partly fund it for eligible homes

Lower Bills

Around £280/year for a semi-detached house (Energy Saving Trust)

No Exterior Change

Leaves outer walls unchanged. Listed buildings still need advice and permission first

Room by Room

Can be planned around redecorating, one room at a time

Warmer Home

Less heat lost through cold solid walls, with fewer draughts

Lower Cost

Generally cheaper than external wall insulation (Energy Saving Trust)

Internal Wall Insulation Costs

Around £12,000
Typical cost for a 3-bed semi, whole house including redecoration

Funding May Help With the Cost

ECO4 ends on 31 December 2026 and work must be finished by then. It is not a grant: work may be fully or partly funded, and you may be asked to contribute. In England, councils also run the Warm Homes: Local Grant (EPC D-G, household income usually £36,000 or less). The Great British Insulation Scheme closed on 31 March 2026.

UK Energy Partnership is run by Harber Glaves Trading Ltd. We are not a government body and cannot decide who gets funding. Check eligibility with the official scheme: ECO4 or Warm Homes: Local Grant.

£140-£500/year
Typical bill savings, flat to detached house (around £280 for a semi)

Typical costs, last reviewed September 2026. Source: Energy Saving Trust, July 2026 prices (unsubsidised, gas-heated home).

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Ready for Internal Wall Insulation?

Sending an enquiry is free. Better Home Hub, which runs this site, introduces installers who may be able to help. Check they are TrustMark registered before you agree to work.

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