London & South-East England
Internal Wall Insulation (IWI)
Internal wall insulation upgrades solid walls from the inside, using insulated boards or a breathable system fitted against the external walls room by room. It is the go-to solution where the outside of the building can't be touched — listed buildings, homes in conservation areas, and flats where you only own part of the façade.
Is IWI right for your home?
- Listed buildings and conservation-area homes where EWI isn't permitted
- Flats and maisonettes where you don't control the whole façade
- Solid-wall period homes where the brick frontage must be preserved
- Homeowners insulating a few rooms at a time rather than the whole house
- Properties needing breathable, moisture-open build-ups
Internal Wall Insulation: key facts
- Best for listed buildings, conservation-area homes and flats where the exterior can't change.
- Typical cost £100–£140/m² — a single room from £1,800, a full 3-bed £8,000–£15,000.
- Build-ups add 50–100mm per external wall — a small floor-area trade-off.
- Breathable wood-fibre and SWIP systems protect older, vapour-open walls from moisture.
- Can be phased one room at a time, and you don't need to move out.
- PAS2030-19 certified, TrustMark registered, written system guarantee.
What is internal wall insulation?
Across areas like Richmond, Chiswick, Wandsworth and Tunbridge Wells, much of the period housing stock falls under conservation restrictions, which makes IWI the practical choice. The key decision is the system: rigid insulated plasterboard maximises thermal performance, while breathable wood-fibre and SWIP systems protect older, vapour-open construction from moisture problems.
We are PAS2030-19 and TrustMark certified, and we specialise in heritage-sensitive installs that respect period fabric — managing reveals, skirtings, sockets and cornicing properly rather than just battening boards to a wall.
Internal Wall Insulation cost guide
Indicative 2026 pricing for London & the South-East, based on hundreds of real quotes and 500+ completed installations — not generic industry averages. Every quote is free, fixed and itemised, with no hidden extras.
| Job type | Indicative cost |
|---|---|
| Single room | £1,800 – £4,000 |
| Typical 3-bed house (full) | £8,000 – £15,000 |
| Breathable wood-fibre system | +15–25% |
| Per m² (board + finish + labour) | £100 – £140 / m² |
What real jobs actually cost
Anonymised prices from recent jobs our own team won and installed across London and the South-East. Every home differs — your fixed, itemised quote follows a free survey.
| When | Area | Work | Size | Price |
|---|---|---|---|---|
| June 2026 | East Dulwich (SE22) | Internal wall insulation | 13 m² | £2,700£216/m² |
| April 2026 | Crystal Palace (SE19) | Internal wall insulation | 14 m² | £2,980£213/m² |
| May 2025 | Watford (WD19) | Internal wall insulation | — | £5,120 |
| April 2025 | Shepherd's Bush (W12) | Internal wall insulation | — | £5,300 |
| January 2025 | Kilburn (NW6) | Internal wall insulation | — | £3,540 |
| January 2025 | Potters Bar (EN6) | Internal wall insulation | — | £5,420 |
| January 2025 | Carshalton (SM5) | Internal wall insulation | — | £3,070 |
| November 2024 | Leyton (E10) | Internal wall insulation | — | £3,900 |
Prices are real totals paid for the specific scope of each job (access, condition and finishes vary) — use them as honest reference points, not like-for-like quotes. Full cost guide
Recent IWI work
Real jobs completed by our own team across London and the South-East.
Internal Wall Insulation using SWIP IWI
SWIP IWI mid install in Croydon
Internal Wall Insulation
Internal wall Insulation in progress
Systems & materials we install
How IWI installation works
Free survey
We assess wall construction and moisture risk, measure each room, and recommend a rigid or breathable system to suit the building.
Specification & quote
A fixed written quote within 24 hours covering board type, finishes, electrical and joinery adjustments.
Installation
Rooms cleared and protected, boards fixed with correct vapour control, then taped, skimmed and made good ready for decoration.
Sign-off & guarantee
Final inspection, TrustMark lodgement and a written system guarantee.
Free survey & fixed quote
Book a free, no-obligation survey and we'll send a clear, fixed written quote within 24 hours — PAS2030-19 certified and TrustMark registered, with all work installed by our own trained team.
Get a free quoteInternal Wall Insulation FAQs
How much does internal wall insulation cost?
How much room will I lose?
Is IWI safe for old, solid walls?
Can I do it one room at a time?
Do I need to move out?
Areas we cover
We install internal wall insulation across London and the South-East. See all areas we cover →
Other insulation services
Deciding between the two? Compare external vs internal wall insulation →
Related guides
In-depth, independent guidance to help you decide.
Last reviewed June 2026 by Stay Warm Insulation.
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