Cavity wall insulation across South Glamorgan
We cover 3 towns in South Glamorgan: Cardiff, Barry and Penarth.
Before any material is chosen, exposure is checked. Parts of South Glamorgan face some of the heaviest wind-driven rain in the UK, especially exposed coastal and upland sites. Here the survey is stricter: some walls suit only certain certified systems, and some should not be filled at all.
Most South Glamorgan houses built from the 1920s onwards have cavity walls, but the survey still checks each one: cavity width, debris, the condition of the brickwork and how exposed each wall is. South Glamorgan properties with rendered or painted walls get a closer look at the outer finish, because cracked render can let rain behind it.
Building Regulations in Wales
In Wales, filling an existing cavity is also notifiable building work under the Building Regulations as they apply in Wales. A registered installer normally self-certifies it through a competent person scheme; otherwise a building notice goes to your council's building control before work starts. Welsh rules can differ from England's, so the notification route is confirmed in writing on your quote.
Funding in Wales
- Warm Homes Nest offers free improvements, including insulation, to eligible low-income owner-occupiers and private renters; eligibility was widened to some households without means-tested benefits.
- Green Homes Wales has been piloting advice and interest-free loans for households above the Nest and ECO4 income thresholds.
- ECO4 runs until 31 December 2026 across Great Britain, including Wales.
Sources: Welsh Government: building work competent person schemes; CIGA: CWISC competent person scheme; Welsh Government: issues arising from cavity wall insulation installations; Welsh Government: warmer and more energy efficient homes (July 2026); GOV.UK: extending the ECO4 end date, government response.
Which material goes in?
Usually blown mineral wool or bonded polystyrene beads, both third-party certified for cavity fill. The survey picks the system that suits your cavity width, wall condition and exposure zone, not whichever is cheapest on the day. Old-style urea-formaldehyde foam is not used.
What is included
- Suitability survey with photos and a written result
- Borescope check where the cavity is in doubt
- Certified mineral wool or bonded bead system
- Drilling, filling and colour-matched making good
- Cavity barriers at party walls
- Building regulations route for your nation, confirmed in writing
- Guarantee and installer named on your quote
Cavity wall insulation prices in South Glamorgan
| Cavity wall insulation guide prices | Guide price |
|---|---|
| Detached house | £2,295–£3,795 |
| Semi-detached house | £1,495–£2,495 |
| End-terrace house | £1,295–£2,195 |
| Detached bungalow | £1,295–£2,195 |
| Semi-detached bungalow | £895–£1,595 |
| Mid-terrace house | £795–£1,395 |
No VAT is charged on installing insulation in homes until 31 March 2027 (then 5%). 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.
What happens next for a South Glamorgan property:
Get in touch
Online, by phone or WhatsApp, whichever suits you.
Survey visit
The surveyor checks each wall and looks into the cavity where needed.
Your result in writing
What we found, what it means, and a fixed price if work is needed.
Booked work
Carried out by the installer named on your quote, with their scheme registrations.