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.

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PAS2030-19 CertifiedTrustMark ApprovedOwn trained team

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

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. Eligible households can have the work funded under ECO4 or the Great British Insulation Scheme.

Internal Wall Insulation cost guide

Indicative 2026 pricing for London & the South-East. Every quote is free, fixed and itemised — grants can reduce or remove these figures for eligible households.

Job type	Indicative cost	Notes
Single room	£1,500 – £3,500	Good way to start and spread cost
Typical 3-bed house (full)	£8,000 – £15,000	All external walls treated
Breathable wood-fibre system	+15–25%	Premium for heritage build-ups
Per m² (board + finish + labour)	£50 – £90 / m²	Useful for rough estimates

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

SWIP (Stay Warm Insulation Plus) internal system

Insulated plasterboard (Kingspan Kooltherm K118)

Breathable wood-fibre boards for period properties

Vapour-control and airtightness membranes

Mineral-wool studwork build-ups where depth allows

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, plus any grant eligibility.

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.

Grants for internal wall insulation

We're TrustMark-registered for ECO4 and the Great British Insulation Scheme. If your household qualifies, this work can be fully or partly funded — we handle the application end-to-end.

Check my eligibility

Internal Wall Insulation FAQs

How much does internal wall insulation cost?

A single room is typically £1,500–£3,500; a full 3-bed house £8,000–£15,000, or roughly £50–£90 per m². Breathable wood-fibre systems for period homes add 15–25%. ECO4/GBIS grants can cover eligible households.

How much room will I lose?

Build-ups are usually 50–100mm per wall depending on the system and the performance target — so a small reduction in floor area on external walls only. We design around windows, radiators and sockets to keep the loss minimal and tidy.

Is IWI safe for old, solid walls?

Yes, when the system matches the wall. Older breathable construction needs a vapour-open build-up (wood fibre) and careful detailing to avoid trapping moisture — which is why specification and PAS2030 certification matter more here than with any other measure.

Can I do it one room at a time?

Absolutely — IWI is the easiest measure to phase. Many clients start with the coldest north-facing rooms and extend over time.

Do I need to move out?

No. We work room by room so the house stays liveable throughout, protecting floors and furniture and containing dust to the active rooms.

Areas we cover

We install internal wall insulation across London and the South-East. See all areas we cover →

Wimbledon Kingston upon Thames Hounslow Ruislip

Other insulation services

External Wall Insulation Loft & Roof Insulation Floor Insulation

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