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London & South-East England

Internal Wall Insulation Installers in London

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.

Get a free quoteCall 020 3411 1408
PAS 2030:2023 certifiedTrustMark 2259022Own trained team, no subcontractors9.87/10 on Checkatrade

What internal wall insulation costs with us

£3,828 to £9,701

The middle half of 108 priced internal wall insulation quotes. Median £5,550.

Typical rate £130 to £140 per m² for the internal wall insulation itself.

Full price breakdown and real jobs

From our quote book of 454 priced quotes. 0% VAT on insulation until 31 March 2027.

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.
  • PAS 2030:2023 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 PAS 2030:2023 and TrustMark certified IWI installers with our own in-house team — no subcontractors — 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. We work across the whole of London: recent internal wall jobs range from Kilburn, Watford and Potters Bar in the north to Teddington, Carshalton and Hounslow in the south and west.

A typical IWI build-up runs, from the cold side to the warm side: the existing solid wall, an insulation layer (boards or an insulated stud system), an air and vapour control layer, and a plasterboard or plaster finish. Total thickness is usually 65 to 95mm; breathable wood-fibre build-ups can be thicker.

On paper the thermal effect matches external insulation. A 9-inch solid brick wall at about 2.1 W/m²K drops to around 0.30 W/m²K with 65 to 95mm of IWI. The rooms feel warmer and the condensation on cold walls stops.

The difference, and the reason IWI is the harder measure to get right, is that you insulate from the warm side. The masonry behind stays cold all winter. Any warm, humid room air that gets past the vapour control layer condenses on that cold wall and is trapped. Moisture control is what separates a good IWI job from a failed one.

Internal Wall Insulation cost in London

Prices from our own quote book and finished jobs in London and the South-East, not national averages. Every quote is free, fixed and itemised after a survey.

Job typeCost
Single roomGood way to start and spread cost£1,800 – £4,000
Typical 3-bed house (full)All external walls treated£8,000 – £15,000
Breathable wood-fibre systemPremium for heritage build-ups+15–25%
Per m², system rateBoard or studs, finish and labour£100 – £140 / m²
Per m², finished room all-inTwo measured single-room jobs incl. making good£213 – £216 / m²

What changes the price

  • How much of the house. Most of our IWI jobs treat a few rooms rather than the whole house, which is why the median job is well below a full-house price.
  • Empty or lived-in rooms. Empty rooms are quicker to work in than rooms we have to work around. See insulating while you live there.
  • Services. Sockets, switches, radiators and pipes all move forward to the new wall face. Lots of surface cabling adds days.
  • Finishing. Skirtings, architraves and cornice reinstatement are real joinery and plastering, covered in why good IWI is a finishing trade.
  • The system. Breathable wood-fibre build-ups sit at the top of the range.

Insulation is zero-rated for VAT until 31 March 2027 (see 0% VAT on insulation). We work on privately funded jobs; for what grant help exists, read our insulation grants guide.

Every figure on this page comes from our quote book. The full dataset, with each finished job listed, is in what insulation really costs in London.

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.

WhenAreaWorkSizePrice
June 2026East Dulwich (SE22)Internal wall insulation13 m²£2,700£216/m²
April 2026Crystal Palace (SE19)Internal wall insulation14 m²£2,980£213/m²
May 2025Watford (WD19)Internal wall insulation—£5,120
April 2025Shepherd's Bush (W12)Internal wall insulation—£5,300
January 2025Kilburn (NW6)Internal wall insulation—£3,540
January 2025Potters Bar (EN6)Internal wall insulation—£5,420
January 2025Carshalton (SM5)Internal wall insulation—£3,070
November 2024Leyton (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 internal wall insulation work

Real jobs completed by our own team across London and the South-East.

Internal Wall Insulation using SWIP IWI

Internal Wall Insulation using SWIP IWI

SWIP IWI mid install in Croydon

Internal Wall Insulation

Internal Wall Insulation

Internal wall Insulation in progress

Is internal wall insulation 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

Choose IWI when:

  • You cannot change the outside: conservation areas, listed buildings, a terrace with a brick front that must stay, or a flat where you do not control the elevation.
  • You want to insulate room by room, starting with the coldest rooms and spreading the cost.
  • You are renovating inside anyway, so the disruption is already happening.
  • The outside is in good condition and you do not want scaffold and render.

IWI is the wrong call when:

  • The wall is actively damp. Fix penetrating or rising damp first, then insulate.
  • You cannot lose room space. 65 to 95mm off each external wall adds up in small rooms.
  • The room has fine cornicing, mouldings or panelling you want to keep. They have to come off and seldom go back the same.
  • You want a quick job. IWI means stripping rooms to the brick, moving furniture and redecorating.

Weighing up inside against outside? Read external vs internal wall insulation, and for older houses insulating a period or listed home.

Internal Wall Insulation systems and materials

The four routes installers actually use, in the order we most often recommend them:

SystemBuild-upBest forCost band
SWIP thermally broken stud system65 to 95mmMost solid-wall homes; engineered for them££
PIR insulated plasterboard52.5 to 92.5mmQuick installs, simple rooms£
Wood fibre with lime plaster80 to 160mmListed and very old houses£££
Mineral wool batten system100 to 150mmUneven walls, or where services run in the wall££

SWIP is what we install on most solid-wall homes, as a manufacturer-approved installer. Its composite EcoStuds insulate instead of cold-bridging like timber or metal studs, with water-repellent mineral wool between them and a taped vapour control membrane on the warm side. The build-up is BBA certified as one tested system and carries a 25-year system guarantee. See our SWIP internal wall insulation guide.

PIR insulated plasterboard is the lower-cost option with a thinner build-up; the vapour detail at junctions is less forgiving. Wood fibre with lime plaster keeps the whole wall vapour-open, so moisture that gets in can dry out again: essential on many pre-1850 and listed homes (see breathable wall insulation). Batten systems suit walls too uneven to bond to. The three board types are compared in PIR vs wood fibre vs insulated plasterboard.

Products we install

SWIP IWI System

Thermally broken stud IWI system

A BBA-certified internal wall insulation system built on thermally broken composite studs with mineral wool infill and a sealed vapour control layer, backed by a 25-year system guarantee. We install it as a manufacturer-approved installer.

0.30 – 0.43 W/m²K · 65 – 95 mmSWIP

PIR Insulated Boards

Polyisocyanurate foam

High-performance rigid PIR boards that achieve excellent U-values in a slimmer profile than mineral wool alternatives — useful where internal space is at a premium.

0.18 – 0.35 W/m²K · 50 – 100 mmCelotex

PIR Insulated Plasterboard

PIR + plasterboard laminate

All-in-one insulation and plasterboard for ceilings and dot-and-dab wall applications. Single-fix solution minimising on-site steps.

0.30 – 0.55 W/m²K · 52.5 – 92.5 mmKingspan

The mistakes that make internal wall insulation fail

Failed IWI jobs almost always show one of these five faults.

1. Gaps in the vapour control

Gaps at sockets, junctions and pipes let warm humid air reach the cold wall behind the insulation. Within two or three winters mould can grow where nobody sees it. See airtightness and vapour membranes.

2. Window reveals left bare

Reveals are thermal weak points. If they are not insulated with at least 25 to 30mm of board, they stay cold and condensation forms round the frame. We insulate reveals as part of the system; see window reveals and sills.

3. Boarding over a damp wall

A wall that has been damp for a century seals its moisture in when closed-cell board goes over it. We damp-test walls before we specify, and treat the cause or choose a breathable system when the readings say so.

4. The floor junction

On a suspended timber floor, cold air from the void can rise behind the new wall. Insulating the floor at the same time closes that route; see floor insulation.

5. No ventilation plan

IWI makes rooms more airtight. Without working extract fans in kitchens and bathrooms, humidity builds up. A ventilation check belongs in every IWI specification; see ventilation after insulating.

How internal wall insulation installation works

1

Free survey

We assess wall construction and moisture risk, measure each room, and recommend a rigid or breathable system to suit the building.

2

Specification & quote

A fixed written quote within 24 hours covering board type, finishes, electrical and joinery adjustments.

3

Installation

Rooms cleared and protected, boards fixed with correct vapour control, then taped, skimmed and made good ready for decoration.

4

Sign-off & guarantee

Final inspection, TrustMark lodgement and a written system guarantee.

Step by step, room by room

  1. Survey. Damp readings on every wall, services photographed, room order and any furniture moves agreed.
  2. Quote. Itemised: strip-out, system, installation, services, making good and waste.
  3. Strip-out. Skirtings and radiators off, sockets and switches moved onto extension boxes, plaster taken back where needed.
  4. Preparation. Loose brick repointed, surfaces cleaned, high spots taken off.
  5. Insulation. Studs or boards fixed, joints taped, the vapour control layer made continuous.
  6. Reveals and junctions. Window reveals, ceiling edge and floor junction detailed with the vapour layer carried through.
  7. Finish. Plasterboard or skim to a paint-ready surface.
  8. Reinstatement. Skirtings, sockets, switches and radiators refitted.

A typical terrace takes 2 to 3 weeks, room by room, and you can stay in the house. Durations for every measure are in how long insulation takes.

Free survey and a fixed quote

Book a free, no-obligation survey and we'll send a clear, fixed written quote within 24 hours: PAS 2030:2023 certified and TrustMark registered, with all work installed by our own trained team.

Get a free quoteCall 020 3411 1408

Internal Wall Insulation across London

Our team installs internal wall insulation across London and the South-East. These local pages carry area-specific advice and nearby jobs. See every area we cover.

Internal Wall Insulation in CroydonInternal Wall Insulation in GreenwichInternal Wall Insulation in SuttonInternal Wall Insulation in BexleyInternal Wall Insulation in OrpingtonInternal Wall Insulation in WimbledonInternal Wall Insulation in WandsworthInternal Wall Insulation in Kingston upon ThamesInternal Wall Insulation in New MaldenInternal Wall Insulation in CarshaltonInternal Wall Insulation in RichmondInternal Wall Insulation in TwickenhamInternal Wall Insulation in HounslowInternal Wall Insulation in ChiswickInternal Wall Insulation in HendonInternal Wall Insulation in RuislipInternal Wall Insulation in Watford

Internal Wall Insulation FAQs

How much does internal wall insulation cost?
A single room is typically £1,800–£4,000 and a full 3-bed house £8,000–£15,000. Across 108 IWI quotes the median project was £5,550, because most jobs treat a few rooms. The system rate is £100–£140 per m²; small rooms finished with making good came to about £213–£216 per m². Breathable wood-fibre systems sit at the top of the range.
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.
Do you cover north London?
Yes — our IWI installers work across the whole of London. Recent internal wall insulation jobs include Kilburn (NW6), Watford (WD19) and Potters Bar (EN6) in the north, alongside our south and west London heartland.
Are you IWI installers or do you use subcontractors?
We install everything with our own trained, PAS 2030:2023 certified team — never subcontractors. One crew and one point of contact from survey to sign-off, which is how we keep a 9.87/10 Checkatrade rating across 500+ installations.
Can I install internal wall insulation myself?
It is possible, but the vapour control detail is exacting and mistakes stay hidden until mould or damp appears. A manufacturer system guarantee also needs an approved installer.
What if I already have damp?
Do not insulate over it. The cause, often a roof, gutter, ground level or pointing fault, must be found and fixed first. We tell you straight if a wall is not ready.
Can I keep my fireplace?
Yes. Chimney breasts can be insulated around or left as they are; live fireplaces keep their safety clearances. See our guide to insulating around chimney breasts.

Guides on internal wall insulation

Detail on the questions homeowners ask us most.

Other insulation services

External Wall InsulationLoft & Roof InsulationFloor InsulationAll services

Last reviewed September 2026 by Stay Warm Insulation.

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