Internal Wall Insulation Cost UK (2026)
Last updated 5 October 2026 · Prices based on the Ofgem price cap (October 2026 – December 2026)
Insulated plasterboard or a stud wall filled with insulation is fixed to the inside of external walls. It's cheaper than external insulation and doesn't change the look of the house, but skirting, sockets and radiators must be refitted.
Internal wall insulation cost payback calculator
At £9,000 net cost and £380 saved a year, it pays for itself in about 23.7 years.
- Net cost
- £9,000
- Payback
- 23.7 yrs
- 10-year saving
- £-5,200
Simple payback = (cost − grant) ÷ annual saving, at today's price cap (26.32p electricity, 7.97p gas). Ignores future price changes.
Internal wall insulation cost by property type
| Property type | Typical cost | Annual saving | Payback |
|---|---|---|---|
| Flat | £3,500–£6,000 | £150–£250 | 20–25 yrs |
| Mid-terrace | £6,000–£9,000 | £250–£330 | 22–28 yrs |
| Semi-detached | £8,000–£11,000 | £330–£430 | 22–27 yrs |
| Detached | £11,000–£14,000 | £450–£520 | 24–28 yrs |
What affects the cost
Method
Insulated plasterboard is quicker; stud walls allow thicker insulation.
Refitting
Moving radiators, sockets and skirting adds cost.
Room count
Can be done one room at a time.
Moisture
Breathable systems may be needed in older homes.
How to reduce the cost
- Do it room by room during redecoration
- Use vapour control to avoid condensation
- Insulate window reveals to prevent cold bridges
- Get a moisture risk assessment for older walls
Frequently asked questions
How much room do I lose?
Typically 60–100mm per insulated wall.
Internal or external — which is better?
External is more effective and keeps space; internal is cheaper and can be phased.
Can I do it myself?
Competent DIYers can fit insulated plasterboard, but detailing around windows is critical.
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.