Group B · Cavity and internal walls
Cavity wall extraction and refill
Failed, wet or slumped cavity insulation removed, wall ties checked, then refilled.
Price by property type
Cavity extraction and refill
- Mid-terrace£2,500–£4,500
- Semi / end-terrace£3,500–£7,500
- Detached£6,000–£11,000
- Bungalow£3,000–£6,000
- Flat / blockBlock survey
Before grants · updated 11 October 2026 · a survey confirms the final figure.
- Best for
- Damp or cold patches after an old fill
- Guarantee or standard
- CIGA claim process; new guarantee
- Time on site
- Typically a few days for a semi, depending on how much material comes out.
- Typical price
- From £2,500
What it is
What is cavity wall extraction and refill?
Failed, wet or slumped cavity insulation removed, wall ties checked, then refilled.
Best for: Damp or cold patches after an old fill.
Build-up
Filled cavity wall
- 1Plaster
- 2Inner leaf
- 3Cavity filled with blown mineral wool or bonded bead
- 4Outer leaf of brick
Who it suits
Which homes is cavity wall extraction and refill suitable for?
Is my home suitable?
Pick your property type for a straight answer on cavity wall extraction and refill.
Guidance only — every home is different, and a survey confirms what suits yours.
Houses
Flats and blocks of flats
Commercial and public buildings
Usually suitable Depends — a survey confirms
Not usually suitable for 9 property types
- Mews house and cottage — Homes of this type usually have solid walls with no cavity to fill. Internal or external wall insulation is the route.
- Period home — Homes of this type usually have solid walls with no cavity to fill. Internal or external wall insulation is the route.
- Non-traditional / system-built — Most system-built homes (concrete panels, no-fines concrete, steel or timber frame) have no conventional cavity to fill. EWI is often the only route.
- Listed building or conservation area — Homes of this type usually have solid walls with no cavity to fill. Internal or external wall insulation is the route.
- Farmhouse, barn conversion or rural home — Homes of this type usually have solid walls with no cavity to fill. Internal or external wall insulation is the route.
- New build or self-build — New homes are built with insulated cavities, so there's nothing to fill.
- Park and mobile home — Park and mobile homes need specialist systems, which we arrange through a partner rather than standard measures.
- Converted flat — Homes of this type usually have solid walls with no cavity to fill. Internal or external wall insulation is the route.
- Mansion block — Homes of this type usually have solid walls with no cavity to fill. Internal or external wall insulation is the route.
Materials and brands
What we use
Remove failed, wet or slumped cavity insulation and debris, check wall ties, then refill with a suitable system.
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 cavity wall extraction and refill 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 |
|---|---|---|---|---|---|
| Cavity extraction and refill | £2,500–£4,500 | £3,500–£7,500 | £6,000–£11,000 | £3,000–£6,000 | Block survey |
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 for a semi, depending on how much material comes out.
Disruption
Done from outside: bricks are removed at intervals, the old fill vacuumed out, then the cavity refilled and the brickwork made good.
Planning and building control
Cavity wall insulation must comply with Building Regulations and is certified through a competent person scheme or building control. Internal wall insulation doesn't need planning, but listed buildings need consent.
Guarantee and standard
CIGA claim process; new guarantee. 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
Cavity wall extraction and refill: your questions answered
How much does cavity wall extraction and refill cost?
Typical installed prices in London and the South East, including VAT and before any grant: £2,500–£4,500 for a mid-terrace; £3,500–£7,500 for a semi-detached or end-of-terrace house; £6,000–£11,000 for a detached house; £3,000–£6,000 for a bungalow; Block survey for blocks of flats. Prices updated 11 October 2026. A survey confirms your final figure.
What are the signs of failed cavity wall insulation?
Damp patches or cold spots on inside walls that appeared after a cavity fill, mould behind furniture on outside walls, or a borescope showing wet, slumped or missing insulation.
How is cavity wall insulation removed?
Bricks are taken out at intervals and the old fill and debris are extracted with industrial vacuum equipment. We then check the wall ties and refill with a suitable system.
Will my original guarantee cover extraction?
It may. If the original installer registered a guarantee, a claim can be made through that process. We'll help you check what's in place.
Should the cavity be refilled after extraction?
Usually yes, once the cause of the failure is fixed and the cavity is clean, with a system suited to the wall's exposure. Occasionally the survey shows another approach is better.
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 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.
Internal wall insulation (IWI)
Insulated plasterboard or stud systems fitted inside solid walls where the outside must not change.
Begin your project
Price cavity wall extraction and refill 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.