Group B · Cavity and internal walls
Narrow and hard-to-treat cavities
Specialist bead or wool systems for narrow, stone-faced, exposed or high-rise cavities.
Priced after survey
Narrow and hard-to-treat cavities
Every job like this is different, so we measure first and give you a fixed written quote. The price depends on:
- The area and access
- What's there now and its condition
- The system and finish you choose
No obligation — your survey confirms what suits and what it costs.
- Best for
- Exposed sites, coastal, blocks
- Guarantee or standard
- System approval for exposure zone
- Time on site
- Cavity fill is usually done in a day for a typical house.
- Typical price
- Priced after survey
What it is
What is narrow and hard-to-treat cavities?
Specialist bead or wool systems for narrow, stone-faced, exposed or high-rise cavities.
Best for: Exposed sites, coastal, blocks.
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 narrow and hard-to-treat cavities suitable for?
Is my home suitable?
Pick your property type for a straight answer on narrow and hard-to-treat cavities.
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
Specialist bead or wool systems for narrow, stone-faced, exposed or high-rise cavities.
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 narrow and hard-to-treat cavities cost?
Priced after survey
Jobs like this vary too much for a fair online price, so we measure first and give you a fixed written quote — with no obligation.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
Cavity fill is usually done in a day for a typical house. Extraction and internal wall insulation take longer and are confirmed at survey.
Disruption
Cavity work is done from outside through small drilled holes, which are filled and colour-matched afterwards. Internal wall insulation means clearing the rooms being done.
Planning and building control
The system must be approved for the wall type, the building height and the exposure zone where the home stands.
Guarantee and standard
System approval for exposure zone. 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
Narrow and hard-to-treat cavities: your questions answered
What makes a cavity hard to treat?
Narrow cavities, stone-faced or random stone walls, homes on exposed or coastal sites, and high-rise blocks. Standard fills aren't always approved for these.
Which systems do you use for hard-to-treat cavities?
Specialist bonded bead or wool systems approved for the wall type and the exposure zone.
Can high-rise cavities be filled?
Sometimes, with a system approved for the height and exposure and in line with fire safety rules. Blocks are assessed through a block survey first.
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.
Internal wall insulation (IWI)
Insulated plasterboard or stud systems fitted inside solid walls where the outside must not change.
Begin your project
Ready to talk about narrow and hard-to-treat cavities?
Tell us about your home and we'll arrange a survey, then a fixed written quote — no obligation.