Cavity wall insulation extraction
Extraction is the only real fix for insulation that is wet, slumped or bridging the cavity. Bricks are lifted out along the base of each wall, the fill is loosened with compressed air and drawn out with an industrial vacuum, and a camera confirms the cavity is clear before the bricks go back.
About £20 to £30 per m² of wall, or £1,600 to £2,400 for a semi-detached house
- The brick outer leaf gets wet in rain and dries out again. It was always meant to.
- The fill is continuous and repels water, so nothing wicks across the cavity.
- Wall ties have a drip in the middle, so water runs off them and down.
- The inner wall stays dry and holds its warmth.
- Fill has slumped, leaving an empty band at the top of the wall that runs cold.
- Mortar droppings or debris on a tie make a bridge for water to cross.
- Wet fill at the base holds water against the inner leaf.
- Damp and mould show inside, often low down or around windows.
- In exposed spots, wind-driven rain soaks right through the brick.
- Bricks are lifted out along the base of each wall to open the cavity.
- Compressed air loosens the fill from above and a vacuum draws it out.
- A borescope camera checks the cavity is clear and the ties are sound.
- The wall dries out before it is refilled or left empty.
Extraction is usually right when
- The survey shows wet or saturated fill. Wet insulation does not dry out in a closed cavity. It keeps passing water to the inner wall.
- The fill has slumped or is patchy. Topping up over failed fill rarely works; the old material has to come out so the new can go in evenly.
- The wall should not have been filled. Very exposed elevations, narrow cavities, timber or steel framed houses and some non-traditional construction.
- The cavity has to be clear for other work. Wall tie replacement, a failed cavity tray or a lender’s condition can all need an empty cavity.
Typical extraction prices
| Item | What it covers | Guide price |
|---|---|---|
| Mid-terrace house | About 45 m² of wall, front and back walls only | £900 to £1,350 |
| Semi-detached bungalow | About 50 m², three walls, single storey | £1,000 to £1,500 |
| Semi-detached house | About 80 m², front, back and one side | £1,600 to £2,400 |
| Detached house | About 120 m², all four walls | £2,400 to £3,600 |
| Scaffold, where needed | Tall gables, three storeys, over conservatories | £300 to £800 |
Guide prices before VAT at £20 to £30 per m², from published UK price guides (2024 to 2026) read November 2026. Bonded or foam fills take longer and sit at the top of the range. Work out your own house.
Extraction is priced after a camera survey. Tell us what the walls are doing and we will find a specialist who covers your area.
Get extraction quotesHow the fill actually comes out
There is no single method, because the fill differs. Loose polystyrene beads and blown mineral wool can be drawn out through openings at the base of the wall. Beads that were bonded with adhesive, and foams that have set, have to be broken up first. The basic sequence is the same.
Opening the wall
Bricks are cut out along the bottom of each elevation, above the damp-proof course, at intervals that let the vacuum hose reach the whole cavity. Some specialists also drill or remove bricks higher up to let them work from above. The removed bricks are kept and relaid, so a careful job leaves little trace once the mortar weathers.
Loosening and drawing out
A lance or hose blowing compressed air is worked down the cavity from above to free the fill, which falls to the openings where an industrial vacuum draws it into sacks. Mineral wool that has matted with water is the slowest: it has to be teased loose a section at a time.
Checking the cavity is clear
A borescope is used throughout to find pockets of fill left behind, mortar snots on the ties and rubble at the base. Clearing that debris matters as much as removing the insulation, because it is often what was bridging the cavity in the first place.
Making good and drying out
The bricks are relaid in matching mortar. If the cavity was wet, it needs time to dry before any refill: several weeks in most cases, longer after a wet winter. A good specialist will tell you how long and check moisture readings before refilling.
How long it takes
Published guides put a whole house at one to three days. A mid-terrace with loose beads can be a day; a detached house with bonded beads or foam on every wall takes longer.
VAT
HMRC’s notice on energy-saving materials zero-rates installing insulation in homes until 31 March 2027. It does not cover removing insulation, so expect VAT on the extraction itself unless your contractor shows you otherwise.
Where our information comes from
- GOV.UK (BEIS): Cavity wall insulation, consumer guide to issues arising on installation (October 2019)
- Historic England: Energy efficiency and historic buildings, insulating early cavity walls (HEAG083, April 2016)
- BRE Good Building Guide 44 Part 2: Insulating masonry cavity walls, principal risks and guidance (2001)
- HMRC: VAT on energy-saving materials and heating equipment (VAT Notice 708/6)
Prices are typical ranges from published UK contractor and trade price guides, read November 2026, before VAT. Guidance is summarised in our own words; it is general information, not advice on your particular house.
How the job gets done
The order most extraction jobs follow. Your specialist may combine steps on a small house.
Camera survey
Fill type and condition, which walls, and whether ties or trays need attention.
Bricks out
Openings along the base of each wall, bricks kept to relay.
Loosen and vacuum
Compressed air from above, industrial vacuum below, checked by camera.
Make good
Bricks relaid, debris cleared, the wall left to dry before any refill.
Questions homeowners ask
Can cavity wall insulation be removed?
How much does cavity wall insulation extraction cost?
Is extraction messy?
Do I need to move out?
Does the wall have to be refilled afterwards?
Will my guarantee pay for extraction?
Keep reading
- Removal and refill
Whether to refill, and with what.
- Wall tie replacement
Often found during extraction.
- Removal cost calculator
Your house type, your walls.
Tell us what the walls are doing
Three short steps. Your postcode, the house and what you are seeing are enough to start. The specialist confirms the detail with a borescope survey before any price is fixed.
Costs you nothing. We hold on to what you send until you have agreed to the extraction specialist we suggest.
Got it. What happens now:
- We find an independent extraction specialist working near you who deals with walls like yours, and email or ring to tell you who they are.
- Your details stay here until you agree to that firm.
- Once you agree, they book a camera survey of the cavity and send a written price. We will not add you to any mailing list or ring you to sell anything.