How much does loft insulation save?
Insulating a loft from nothing to 270 mm saves about £360 a year in a detached house, £190 in a semi-detached house, £140 in a mid-terrace and £350 in a detached bungalow, according to Energy Saving Trust figures published by Which? in October 2026, based on gas heating and July 2026 fuel prices.
| Home | 0 to 270 mm, saving a year | 120 to 270 mm, saving a year |
|---|---|---|
| Detached house | £360 | £35 |
| Semi-detached house | £190 | £17 |
| Mid-terrace house | £140 | £13 |
| Detached bungalow | £350 | £35 |
How long does loft insulation take to pay back?
From bare joists, most houses recover the cost in a few years, and the Energy Saving Trust says loft insulation lasts around 40 years. A top-up from 100 mm or more pays back far more slowly, so it is worth doing for comfort, the EPC or alongside other loft work.
How much heat is lost through an uninsulated roof?
The Energy Saving Trust estimates that an uninsulated home can lose around a quarter of its heat through the roof.
When is loft insulation not worth doing?
- The loft already has 270 mm or more in good condition
- The roof leaks, which needs fixing first
- The loft is used as a room, in which case rafter or room-in-roof insulation is the answer
Related services
Sources: Energy Saving Trust: roof and loft insulation; Which?: loft insulation costs and savings; LABC: building regulation requirements for loft insulation; GOV.UK: extending the ECO4 end date, government response; GOV.UK: VAT on energy-saving materials (notice 708/6); Property Care Association: spray foam guidance.