Cavity insulation for new builds and extensions across Hertfordshire
We cover 17 towns in Hertfordshire, including Watford, Hemel Hempstead, Stevenage, St Albans, Welwyn Garden City and more.
Local weather affects which walls can be filled. Much of Hertfordshire sits in the more sheltered driving-rain zones of the UK, which widens the choice of fill. Exposed elevations, coastal sites and high ground still get checked wall by wall.
Where a Hertfordshire property has an extension or a conservatory, we check how the old and new walls meet, because that junction is often missed. A suitable wall in Hertfordshire is usually filled in a single day from outside, with drill holes made good to match the pointing.
Building Regulations in England
Filling an existing cavity wall is notifiable building work in England. Either a building notice goes to building control before the work, or the installer self-certifies it through a government-approved competent person scheme such as CIGA's CWISC scheme. The insulation used must also be suitable for the wall it goes into, which is why the survey checks construction, condition and exposure first.
Funding in England
- ECO4, the energy-supplier scheme, has been extended to 31 December 2026 and government has said there will be no successor supplier obligation.
- The Great British Insulation Scheme closed as planned on 31 March 2026.
- Warm Homes: Local Grant supports low-income households in England through councils, and the January 2026 Warm Homes Plan sets out fully funded upgrades for low-income homes, with more detail still being published.
Sources: Planning Portal: cavity wall insulation and building regulations; CIGA: CWISC competent person scheme; GOV.UK: extending the ECO4 end date, government response; GOV.UK: Warm Homes Plan.
Extensions that join an older house
Where an extension meets an existing cavity wall, the junction is a weak point. We can borescope and fill the existing wall at the same time so the old and new walls perform together.
What is included
- Batts or boards to the specified U-value
- Clean-cavity working
- Trays, closers and stop ends as drawn
- Coordination with your bricklayers
- Photo record for building control
Cavity insulation for new builds and extensions prices in Hertfordshire
| Cavity insulation for new builds and extensions guide prices | Guide price |
|---|---|
| Full-fill batts supplied and fitted, per m² | £9–£16 |
| Partial-fill boards supplied and fitted, per m² | £14–£26 |
Prices are shown before any VAT; the VAT treatment for new-build work is confirmed on your quote. Guide ranges only: the fixed price is confirmed in writing before any work starts, and anything that could not be seen at survey is agreed with you first.
From enquiry to finish in Hertfordshire:
Send your details
A minute online, or call the free number.
We check the walls
Construction, cavity width, debris, damp and wind-driven rain exposure.
You decide
Plain-English result and a fixed price, with no pressure to book.
Job done properly
Holes made good, paperwork handed over, guarantee details confirmed.