The short answer
Cavity wall insulation extraction is normally priced per square metre of external wall, because that is what determines how much drilling and vacuuming the job needs. UK rates sit in a modest per-square-metre range that covers the borescope survey, the drilling pattern, vacuum extraction, verification and making good. The rate is lower per m² on large, easy-access walls and higher on small jobs or where scaffolding is needed, because fixed set-up costs are spread over fewer metres. Damp, slumped or foamed fill pushes the rate up because it is slower to remove than free-flowing EPS bead. To estimate your own job, measure the height and width of each external wall, subtract windows and doors, and multiply the total area by the quoted rate.
Quoting by the square metre is standard across the extraction trade, but the headline rate hides a few variables that explain why a small terrace and a large detached house can have very different per-m² figures.
Extraction per m²
- Pricing basisExternal wall area in m²
- Lower rateLarge, single-storey, easy access
- Higher rateSmall jobs, scaffold, damp fill
- What it coversSurvey, drilling, vacuum, making good
- DIY estimateWall area × quoted rate
Why per-square-metre is the standard unit
Extraction work scales with wall area, not with the number of rooms or floors. A larger wall needs more drill holes, more time under suction and more material removed, so the trade prices by the square metre of treated external wall. This unit also lets a homeowner get the work priced up on a like-for-like basis — two firms quoting different totals can be checked by working back to their per-m² rate.
One nuance: the rate is rarely flat. Most of the cost in a small job is fixed (travelling, setting up the vacuum unit, the survey), so a tiny wall carries a high effective per-m² rate, while a big house spreads those fixed costs and brings the per-m² figure down.
What pushes the per-m² rate up or down
The same square metre of wall can cost very different amounts depending on what is in the cavity and how easy the wall is to reach.
| Factor | Lower per-m² rate | Higher per-m² rate |
|---|---|---|
| Job size | Large total wall area | Small one-wall job |
| Access | Ground floor, open frontage | Upper storeys needing scaffold |
| Fill type | Free-flowing EPS bead | Damp fibre or set UF foam |
| Wall state | Sound, dry brickwork | Crumbling mortar, repointing needed |
| Region | Areas with more competition | Remote or high-cost areas |
Indicative influences on the per-square-metre extraction rate. Fixed set-up costs make small jobs dearer per m².
Estimating your own wall area
You can get a rough feel for the cost before any survey by measuring the walls yourself:
- Measure each external wall — height from damp-proof course to eaves, and width corner to corner.
- Multiply height × width for each wall to get its area in square metres.
- Subtract openings — deduct the area of large windows and doors, which have no cavity to extract.
- Add the walls together for a total treated area.
- Multiply by the quoted per-m² rate for a ballpark figure, remembering small jobs attract a higher rate.
This is only an estimate — the borescope survey may reveal damp or foamed fill that changes the rate — but it stops the headline total feeling arbitrary and lets you sanity-check a quote.
Frequently asked questions
Why do small extraction jobs cost more per square metre?
Because much of the cost is fixed — travel, set-up and the borescope survey happen regardless of wall size. On a small job those fixed costs are spread over fewer square metres, so the effective per-m² rate is higher than on a whole-house extraction.
Does the per-m² rate include making good the holes?
Usually yes. A standard extraction rate covers the survey, drilling, vacuuming, verification and repointing the access holes. Confirm that repointing and waste disposal are included rather than charged separately.
How do I estimate my wall area?
Measure the height and width of each external wall, multiply them for each wall's area, subtract large windows and doors, then add the walls together. Multiplying that total by the quoted per-m² rate gives a rough cost.
Sources & further reading
- Checkatrade — cavity wall insulation removal cost guide
- MyJobQuote — cavity wall insulation removal cost guide
- CIGA — Cavity Insulation Guarantee Agency
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property. They are guidance, not a quotation.