The short answer
Insulating a solid brick wall externally costs roughly £90–£150 per square metre fitted in the UK, so a single elevation might be £3,000–£6,000 and a whole solid-walled house £10,000–£20,000. Solid brick walls — common in homes built before about 1920 — have no cavity, so they lose heat far faster than modern cavity walls, with an uninsulated U-value around 2.0 W/m²K. An external system of insulation board and render can bring that down to roughly 0.30 W/m²K or better, depending on thickness. The fitted rate covers boards, render, mesh and labour; scaffolding, prep and the render finish move it. These are typical ranges, not fixed quotes.
Solid brick walls are the classic case for external insulation because they have no cavity to fill. Here is the cost and the performance you can expect.
Solid brick at a glance
- Per square metre fitted~£90–£150 / m²
- Single elevation£3,000–£6,000
- Whole house£10,000–£20,000
- Uninsulated U-value~2.0 W/m²K
- After EWI~0.30 W/m²K or better
Why solid brick walls are the prime candidate
Homes built before roughly 1920 typically have solid walls — a single thickness of brick (often 9 inches / 215mm) or stone with no gap inside. Because there is no cavity, you cannot use the cheaper cavity-fill insulation that suits post-war houses; the only practical options are insulating from the outside (EWI) or the inside (IWI). Solid walls lose heat quickly, with an uninsulated U-value around 2.0 W/m²K, so they are where external insulation delivers the biggest improvement.
| Measure | Typical rate | U-value effect |
|---|---|---|
| Solid wall, uninsulated | — | ~2.0 W/m²K |
| External insulation (EWI) | £90–£150 / m² | down to ~0.30 W/m²K |
| Internal insulation (IWI) | £60–£110 / m² | similar U-value, loses floor space |
| Single elevation (EWI) | £3,000–£6,000 | depends on area |
Indicative UK figures for guidance, 2026. Sources: Energy Saving Trust solid wall insulation guidance.
External versus internal on a solid wall
EWI and internal wall insulation reach a similar U-value, but they differ in cost and disruption. External insulation wraps the outside, so it does not reduce room sizes, keeps the wall's thermal mass on the warm side, and re-weatherproofs the building — but it costs more and changes the external appearance. Internal insulation is cheaper per square metre but eats into floor space, needs rooms cleared and decoration redone, and has to be detailed carefully to avoid trapping moisture. For most solid-walled homes that can change their exterior, EWI is the preferred route despite the higher price.
What moves the price on a brick wall
The cost drivers are the same as any EWI job but a few are sharper on old brick. The condition of the wall matters: spalled, soft or previously painted brick may need cleaning, repair or a key coat before boards go on. Thickness of insulation affects both performance and detailing — a thicker board reaches a lower U-value but needs more allowance at reveals and eaves. The render finish (basic versus silicone, textured or brick-effect) and scaffolding on a two-storey house add to the total. Planning can also be a factor: in a conservation area or on a listed building, external changes may need consent, and a brick-effect or like-for-like finish may be required.
Grant-funded work under ECO4 or the Great British Insulation Scheme must meet PAS 2030/2035 and be done by a TrustMark-registered installer. And qualifying EWI in Great Britain attracts 0% VAT on installed energy-saving materials under the relief running to 31 March 2027.
Is it worth insulating solid brick externally?
For a cold, hard-to-heat solid brick home, EWI is one of the most effective fabric upgrades available. Cutting the wall U-value from around 2.0 to roughly 0.30 W/m²K sharply reduces heat loss through what is usually the largest surface of the building, removes cold internal wall surfaces where condensation and mould form, and improves the EPC rating. It also re-weatherproofs ageing brickwork in the same operation.
The honest counterweights are the upfront cost, the change to the building's character, and the need to choose a build-up suited to an old, breathable wall so moisture is not trapped. On a heritage or listed property, consent and finish requirements can complicate matters. Where the wall is solid stone rather than brick, breathability and detailing matter even more. A survey by someone experienced with traditional construction will confirm the right system and a real cost; the figures here are typical ranges to set expectations.
The choice of insulation thickness on a solid brick wall is a balance between performance, cost and detailing, and it is worth understanding before you accept a quote. A thicker board reaches a lower U-value and saves more energy, but it adds material cost, projects further from the wall, and demands more allowance at window reveals, the eaves and the damp-proof course. As a rough guide, common EWI thicknesses on solid walls fall in the 90–120mm range, which typically brings the wall comfortably below 0.30 W/m²K; going thicker yields diminishing returns for the extra cost and detailing. On a brick wall with shallow reveals, very thick insulation can leave windows looking recessed unless the reveals are carefully handled. A good installer will recommend a thickness that meets the target U-value (and any grant requirement) while keeping the proportions of the building sensible — and will explain the trade-off rather than simply quoting the thickest, most expensive option.
Costs beyond the wall: detailing on old brick
On a solid brick property, a good part of the price — and the long-term success of the job — lives in the detailing, not the bare wall area. Older brick houses tend to have features that take skilled time to insulate around: decorative brick bands, string courses, arched window heads, projecting cills and ornate door surrounds. Wrapping these cleanly, or recreating their lines in render, is slower than running insulation across a plain modern wall, which is one reason period homes can sit at the upper end of the per-square-metre range. The damp-proof course needs to be respected so the insulation stops above it and the wall can still shed ground moisture, and any airbricks serving underfloor ventilation must be kept clear with proportioned sleeves through the new system.
These details are not optional extras — getting them wrong on a breathable old wall is exactly what leads to trapped moisture, damp patches and render failure later. That is why an installer experienced specifically with traditional and pre-1920s construction is worth more than the lowest quote on a solid brick home. When you read a quote for solid brick, look for evidence that the installer has thought about the damp-proof course, airbricks, reveals and any decorative brick features, and has specified a build-up that lets the wall breathe. A price that simply states a board, a render and a rate, with no mention of how the old wall's quirks will be handled, may be cheaper on paper but riskier on a heritage brick property.
Frequently asked questions
How much does it cost to insulate a solid brick wall externally?
Roughly £90–£150 per square metre fitted. A single elevation might be £3,000–£6,000 and a whole solid-walled house £10,000–£20,000, depending on wall area, system and prep.
What U-value does external insulation reach on a solid brick wall?
An uninsulated solid brick wall has a U-value around 2.0 W/m²K. An external insulation and render system can bring that down to roughly 0.30 W/m²K or better, depending on the insulation thickness used.
Should an old solid brick wall use a breathable insulation system?
Often yes. Older solid brick and stone walls usually need to dry outwards, so a vapour-open system such as mineral wool with a breathable render is frequently preferred to avoid trapping moisture. The build-up should be specified for the wall type.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property. They are guidance, not a quotation.