External Wall Insulation Cost UK (2026)
Last updated 5 October 2026 · Prices based on the Ofgem price cap (October 2026 – December 2026)
For solid-walled homes (mostly built before 1920), insulation boards are fixed to the outside walls and finished with render or brick slips. It avoids losing indoor space but usually needs scaffolding and may need planning permission.
External wall insulation cost payback calculator
At £14,000 net cost and £450 saved a year, it pays for itself in about 31.1 years.
- Net cost
- £14,000
- Payback
- 31.1 yrs
- 10-year saving
- £-9,500
Simple payback = (cost − grant) ÷ annual saving, at today's price cap (26.32p electricity, 7.97p gas). Ignores future price changes.
External wall insulation cost by property type
| Property type | Typical cost | Annual saving | Payback |
|---|---|---|---|
| Mid-terrace | £8,000–£12,000 | £250–£350 | 25–35 yrs |
| Semi-detached | £12,000–£16,000 | £380–£480 | 28–35 yrs |
| Detached | £16,000–£22,000 | £500–£620 | 30–35 yrs |
| Bungalow | £10,000–£14,000 | £350–£450 | 28–32 yrs |
What affects the cost
Wall area
Priced per m² of wall.
Finish
Render is cheapest; brick slips cost more.
Scaffolding
Usually £1,000–£3,000.
Planning
Conservation areas often require permission.
Detailing
Moving pipes, extending window sills and eaves add cost.
How to reduce the cost
- Combine with planned re-rendering to share scaffolding costs
- Check planning rules with your council first
- Ask for a PAS 2035 retrofit assessment
- Look for ECO4 funding if eligible
Frequently asked questions
Is external wall insulation worth it?
In solid-wall homes it substantially cuts heat loss and improves comfort, though financial payback is long.
Do I need planning permission?
Often not, but you may in conservation areas or if it changes the appearance significantly.
How long does it last?
A well-installed system lasts 30+ years.
Sources and methodology
Energy prices come from the Ofgem price cap for Direct Debit customers (GB average). Installation costs are typical UK ranges from installer quotes and industry guidance, rounded. Savings use today's rates and do not predict future prices.