Group B · Cavity and internal walls
Internal wall insulation (IWI)
Insulated plasterboard or stud systems fitted inside solid walls where the outside must not change.
Price by property type
Internal wall insulation (whole home)
- Mid-terrace£7,000–£14,000
- Semi / end-terrace£10,000–£20,000
- Detached£15,000–£30,000
- Bungalow£9,000–£18,000
- Flat / block£5,000–£10,000
Before grants · updated 11 October 2026 · a survey confirms the final figure.
- Best for
- Solid walls where the outside must not change
- Guarantee or standard
- PAS 2035; condensation risk analysis
- Time on site
- Typically a few days per room, including making good ready for decoration.
- Typical price
- From £5,000
What it is
What is internal wall insulation?
Insulated plasterboard or stud systems fitted inside solid walls where the outside must not change.
Best for: Solid walls where the outside must not change.
Build-up
Internal wall insulation
- 1Plaster skim
- 2Insulated plasterboard, or stud with mineral wool
- 3Vapour control, detailed at floors and reveals
- 4Existing solid wall
Who it suits
Which homes is internal wall insulation suitable for?
Is my home suitable?
Pick your property type for a straight answer on internal wall insulation.
Guidance only — every home is different, and a survey confirms what suits yours.
Houses
- Detached house
- Semi-detached house
- End-of-terrace
- Mid-terrace
- Townhouse
- Mews house and cottage
- Detached bungalow
- Semi and terraced bungalow
- Chalet and dormer bungalow
- Period home
- 1930s home
- Post-war and ex-council house
- Non-traditional / system-built
- Listed building or conservation area
- Farmhouse, barn conversion or rural home
- New build or self-build
Flats and blocks of flats
Commercial and public buildings
Usually suitable Depends — a survey confirms
Not usually suitable for 1 property type
- Park and mobile home — Park and mobile homes need specialist systems, which we arrange through a partner rather than standard measures.
Materials and brands
What we use
Insulated plasterboard (PIR or phenolic-backed), timber or metal stud with mineral wool, or breathable wood-fibre and lime systems for solid walls.
Insulation brands we work with
- Knauf Insulation (Earthwool, Supafil blown)
- Rockwool
- Superglass
- Isover
- Kingspan
- Celotex
- Recticel
- Xtratherm
- Steico wood-fibre
- YBS and Actis multifoil
The exact system and brand for your home are confirmed in your written quote.
Heat, bills and EPC
What it does for your heat loss, bills and EPC
An empty cavity lets heat pass straight through the wall. Filling it lowers the wall's U-value considerably, so rooms hold their heat for longer and the heating runs less — often one of the best-value measures on an EPC for homes with unfilled cavities. Solid walls lose even more heat; lining them inside gives a similar improvement, room by room.
See the EPC points and savings for your home in the EPC plannerU-value before and after, typical heat and bill saving, and EPC points — worked out for your property.Price
How much does internal wall insulation cost?
Prices change with your property type. Pick your column — the quote builder then refines it for your home.
| Measure | Mid-terrace | Semi / end-terrace | Detached | Bungalow | Flat / block |
|---|---|---|---|---|---|
| Internal wall insulation (whole home) | £7,000–£14,000 | £10,000–£20,000 | £15,000–£30,000 | £9,000–£18,000 | £5,000–£10,000 |
Indicative ranges for London and the South East, supplied and installed, including VAT, before grants. Updated 11 October 2026. A survey confirms your final price.
0% VAT on energy-saving materials
Insulation, solar panels, batteries and heat pumps installed in homes in Great Britain are zero-rated for VAT until 31 March 2027. Windows and doors are not included.What to expect
Time on site, disruption and approvals
Time on site
Typically a few days per room, including making good ready for decoration.
Disruption
High in the rooms being done: they're cleared, and radiators, sockets and skirtings are moved and refitted. Rooms lose a little floor space.
Planning and building control
No planning permission, as the outside doesn't change. Building Regulations apply, listed buildings need consent, and a condensation risk analysis comes first. Funded jobs follow PAS 2035.
Guarantee and standard
PAS 2035; condensation risk analysis. The guarantee and certification for your job are confirmed in writing in your quote.
60-second grant check
Could a grant help pay for it?
Grant eligibility checker
About 60 seconds · plain results: likely, possibly or not eligible
Before we start
What type of property is it?
Questions
Internal wall insulation (IWI): your questions answered
How much does internal wall insulation cost?
Typical installed prices in London and the South East, including VAT and before any grant: £7,000–£14,000 for a mid-terrace; £10,000–£20,000 for a semi-detached or end-of-terrace house; £15,000–£30,000 for a detached house; £9,000–£18,000 for a bungalow; £5,000–£10,000 for a flat. Prices updated 11 October 2026. A survey confirms your final figure.
What is internal wall insulation?
Insulation fixed to the inside of external walls — insulated plasterboard, or a timber or metal stud wall filled with mineral wool — then plastered. It's the usual route for solid walls where the outside must not change.
How much room space will I lose with internal wall insulation?
Some, because the walls get thicker. The amount depends on the system — slim PIR or phenolic-backed boards lose least. We show the options for each room at survey.
Why do you need a condensation risk analysis?
Insulating inside makes the old wall colder, which can move where moisture condenses. We check each wall build-up first, and detail the floors, ceilings and reveals carefully.
Do I have to insulate every room at once?
No. Many people do one room or one elevation at a time, often when redecorating. We plan the junctions so later rooms join up.
Group B
More in cavity and internal walls
Cavity wall insulation
A borescope survey, then blown mineral wool or bonded bead injected into empty cavity walls.
Cavity wall extraction and refill
Failed, wet or slumped cavity insulation removed, wall ties checked, then refilled.
Cavity wall tie replacement
Replacing corroded wall ties, often found during cavity extraction.
Cavity survey only
Borescope and thermal imaging to show whether a wall is empty, part-filled or failed.
Party wall cavity insulation
Filling cavity party walls to stop hidden 'party wall bypass' heat loss.
Narrow and hard-to-treat cavities
Specialist bead or wool systems for narrow, stone-faced, exposed or high-rise cavities.
Begin your project
Price internal wall insulation in two minutes
See a price range for your property type, with grants and 0% VAT applied where they fit. A survey always confirms the final figure.