Types of Insulation and Costs in Wales 2026
Cavity wall insulation is the most common upgrade for Welsh homes built after the 1920s. Most 1930sā1990s properties have an unfilled cavity that can be filled in a day.
| Insulation type | Typical cost (Wales, 2026) |
|---|---|
| Cavity wall insulation (semi-detached) | Ā£400āĀ£900 |
| Cavity wall insulation (detached) | Ā£600āĀ£1,400 |
| Loft insulation (semi-detached, 270mm) | Ā£300āĀ£600 |
| Loft insulation (detached, 270mm) | Ā£400āĀ£800 |
| External wall insulation (EWI, per sq m) | Ā£80āĀ£150 |
| Internal wall insulation (IWI, per sq m) | Ā£40āĀ£90 |
| Underfloor insulation (suspended floor) | Ā£400āĀ£1,200 |
External wall insulation (EWI) is the main option for solid-wall Welsh properties ā Victorian and Edwardian terraces, older stone cottages. EWI is more expensive than cavity fill but provides both insulation and weatherproofing. A typical 3-bed terrace in South Wales can cost Ā£8,000āĀ£20,000 for full EWI.
Loft insulation at 270mm (the recommended minimum) reduces heat loss through the roof significantly. Wales's climate makes this one of the most cost-effective retrofits available.
Warm Homes Grants for Insulation
The Welsh Government Warm Homes Programme is the primary route for grant-funded insulation in Wales. Eligible households can receive:
- Cavity wall and loft insulation at no cost
- EWI with significant grant contribution
- Combined packages (insulation + heat pump + solar) for qualifying properties
ECO4 (UK-wide energy company obligation) also funds insulation for households on qualifying benefits ā energy suppliers deliver this, so approach them directly or via an approved broker.
For private landlords in Wales, the Minimum Energy Efficiency Standards (MEES) require EPC ratings of E or above ā upgrading insulation is often the most cost-effective way to improve EPC ratings for lower-rated properties.