Cavity wall insulation across Gwynedd
We cover 4 towns in Gwynedd: Bangor, Caernarfon, Holyhead and Porthmadog.
Every elevation is judged on its own exposure. Parts of Gwynedd 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 Gwynedd 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. A suitable wall in Gwynedd is usually filled in a single day from outside, with drill holes made good to match the pointing.
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.
Is my wall suitable for cavity wall insulation?
Most homes built from the 1920s onwards have cavity walls, but having a cavity is not the same as being suitable. The Energy Saving Trust's rule of thumb is a cavity of at least 50mm, clear of rubble, behind masonry in good condition, on a wall that is not exposed to severe driving rain or flood risk.
That is what our survey checks: wall construction and thickness, cavity width and cleanliness (with a borescope where needed), the state of bricks, pointing, gutters and downpipes, any existing damp, and the exposure of each elevation. If a wall should not be filled, you will be told so in writing, with the reason.
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 Gwynedd
| 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.
From enquiry to finish in Gwynedd:
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.