Internal Wall Insulation Grants UK: ECO4 IWI vs External Wall Options

Internal wall insulation grants are not a single government pot: some UK households in solid-wall homes may get support for internal wall insulation (IWI) through ECO4, Help to Heat, or related routes when the property and household qualify and a survey supports the measure. IWI is not automatic free insulation for every solid-wall home. Apply Free Boiler is run by Reliant Energy Solutions Ltd, an ECO4 installer — not government, Ofgem, a council or a supplier.

Short answer: can you get internal wall insulation grants?

Some UK households in solid-wall homes may get support for internal wall insulation (IWI) through ECO4, Help to Heat, or related routes when the property and household qualify and a survey supports the measure. IWI is not automatic free insulation; age or “solid wall” alone is not enough.

• Start with our grants directory and a soft eligibility check — not assumptions about a free install. Our insulation grants guide covers loft, cavity, solid-wall and floor measures together.
• ECO4 runs to 31 December 2026; funding and local capacity may tighten sooner.

For how the scheme works, see our ECO4 scheme guide.

Can I get my walls insulated for free?

Possibly, but not automatically. If you qualify under ECO4 (a listed benefit or a council ECO4 Flex referral), the home meets the EPC rule and a survey supports the measure, internal wall insulation may be funded at little or no cost. Ofgem says energy suppliers decide the level of funding and may ask you to contribute.

Per GOV.UK , owners need an EPC band of D to G, and private tenants need E to G plus the owner’s permission. Run the free ECO4 eligibility check to see which route may fit, and read the Ofgem ECO FAQs for contribution rules.

What internal wall insulation (IWI) is — and when solid walls need it

Internal wall insulation adds insulation to the inside face of external walls. It is common for solid-wall homes (no cavity) where external cladding is impractical — for example because of planning, appearance, access, or the trade-offs your household and surveyor discuss. We do not quote install costs or grant amounts here.

Solid wall means external walls built without a cavity that can be filled. Cavity wall construction has a gap between inner and outer leaves — that gap is usually treated with cavity fill, not IWI. A survey confirms wall type; do not guess from age alone.

Searchers also use solid wall insulation grant language. That umbrella can mean IWI or external wall insulation (EWI). This page stays IWI-primary; if external cladding is the better fit, see external wall insulation grants.

IWI vs external wall vs cavity: which grant path fits

1. Cavity walls → cavity-fill path. See cavity wall insulation grants (do not assume IWI).
2. Solid walls — external preferred → EWI. See external wall insulation grants.
3. Solid walls — internal preferred or practical → IWI focus on this page, subject to survey and scheme rules.

Apply Free Boiler does not decide which measure you get. Scheme rules, the property survey, and an appropriately registered installer pathway decide whether IWI, EWI, cavity fill, loft insulation, or another measure is supported.

ECO4 routes for internal wall insulation

ECO4 (Energy Company Obligation) is the Great Britain scheme under which obligated energy suppliers fund eligible energy-efficiency measures after assessment. For many private households, Help to Heat qualifying benefits are the main route — verify the live list on GOV.UK Energy Company Obligation ; we do not reproduce a full benefits table here.

If you are not on Help to Heat benefits, LA Flex (ECO4 Flex) may be available where your council publishes a Statement of Intent — criteria vary. See LA Flex and Statement of Intent and Warm Homes Local Grant vs ECO4 for alternate pathfinding.

SERP results often mix Great British Insulation Scheme (GBIS) with ECO4. GOV.UK says GBIS installations had to be complete by 31 March 2026, when that scheme ended. For disambiguation see Great British Insulation Scheme guide. GBIS is not Apply Free Boiler's primary product path; ECO4 and Help to Heat framing is usually the better fit for IWI under the obligation scheme.

ECO4 is scheduled to run to 31 December 2026. Context: what the ECO4 deadline means. Primary source: Ofgem ECO .

How much does it cost to insulate internal walls?

It depends on the wall area, the condition of the walls, the finishes and the installer’s quote, so there is no single figure. If ECO4 funds the work you may pay nothing or a contribution; Ofgem says suppliers decide the level of funding.

We do not quote install costs here. If you are paying privately, get written, itemised quotes from more than one installer after a survey. The Energy Saving Trust solid wall insulation guide gives typical costs.

Can I get a grant for underfloor insulation?

Possibly. Ofgem lists underfloor insulation among the measures ECO4 can fund, so eligible households may get it supported where a survey supports it. It is not a separate scheme or a cash grant, and the same eligibility rules apply.

Our insulation grants guide covers floor insulation alongside loft, cavity and solid-wall measures, and the free eligibility check shows which route may fit. Funding and the measure are never guaranteed.

What a survey usually checks for IWI

A property survey under ECO4 or related routes is what turns “maybe eligible” into a supported measure. Typical checks include:

• Wall type — solid vs cavity, and existing insulation.
• Room layout and space impact (IWI reduces internal room size slightly).
• Ventilation and moisture risk at a high level — professional install matters; this is not DIY advice.
• EPC and wider property suitability under live scheme rules.

Funding and installation proceed only if you are eligible under scheme rules, the survey supports IWI (or another measure), and work is delivered through TrustMark / scheme-appropriate installers. We do not promise “free IWI for all solid-wall homes” or invent bill savings figures.

Is it worth getting internal wall insulation?

It can be in a solid-wall home, particularly where external insulation is impractical, because it reduces heat loss through the walls. Weigh the points below, and ask the survey about damp and ventilation before you agree. We do not quote bill savings.

• The work happens inside the rooms, so expect disruption and a small loss of room space.
• Installer quality matters. GOV.UK says there are quality issues with some solid wall insulation fitted under ECO since April 2022, and its guidance on poor quality wall insulation says internal wall insulation showed fewer issues than external.
• If external cladding is the better fit for your home, compare external wall insulation grants too.

How Apply Free Boiler helps (we are not the government or installer)

Apply Free Boiler is run by Reliant Energy Solutions Ltd, an ECO4 installer, working on ECO4 and related pathways — including insulation measures where they apply. We check eligibility and paperwork and, where a route looks viable, our team surveys, installs and submits the work under ECO4 and is paid by the energy supplier, not by you. We are not the government, not Ofgem, not a council and not an energy supplier.

Eligibility is not a guarantee of free IWI or any specific measure. Cold-call pressure is a red flag — see is the free boiler grant a scam?

Related wall insulation grants (EWI, cavity and loft)

This page covers internal wall insulation. Use these guides for other measures:

• Insulation grants overview
• External wall insulation grants
• Cavity wall insulation grants
• Loft insulation grants

Pensioners comparing loft support: loft insulation grant for pensioners.

Deeper EWI reading (when external is the better solid-wall route): external wall insulation grant guide.

Internal wall insulation grant FAQs