If you are paying for insulation yourself, insulating an empty loft and draught proofing pay back fastest, in around four years each. Cavity wall insulation comes next at around a decade, while floor and solid wall insulation take several decades to repay their cost from bill savings alone.
Every cost and saving below comes from the Energy Saving Trust (EST), for a gas-heated home in Great Britain, based on fuel prices as of July 2026. We have only divided the typical installation cost by the typical yearly saving to get a simple payback: the number of years of savings it takes to cover the cost. It ignores future price changes, grants and the 0% VAT on installed energy-saving materials, so treat it as a way to compare measures, not a promise.
What is the ranking?
For a typical semi-detached house, the order from quickest to slowest payback is:
- Loft insulation, 0mm to 270mm: around £750 to install, saving around £190 a year — about 4 years.
- Draught proofing windows, doors and floors: around £250 professionally, saving around £55 a year — about 4½ years (less if you do it yourself).
- Cavity wall insulation: around £2,200, saving around £200 a year — about 11 years.
- Loft top-up, 120mm to 270mm: around £600, saving around £17 a year — about 35 years.
- Suspended timber floor insulation: around £2,200, saving around £55 a year — about 40 years.
- Internal wall insulation (solid walls): around £12,000, saving around £280 a year — about 43 years.
- External wall insulation (solid walls): around £15,000, saving around £280 a year — about 54 years.
The headline is simple: if your loft is empty or your home is draughty, start there. You can try your own house type in our savings calculator, which uses the same EST figures.
Does the ranking change with house type?
Not much. The EST publishes loft and cavity wall figures for several house types, and the order stays the same.
Loft insulation, 0mm to 270mm
- Detached house: around £1,100, saving around £360 a year — about 3 years
- Detached bungalow: around £1,200, saving around £350 a year — about 3½ years
- Semi-detached house: around £750, saving around £190 a year — about 4 years
- Mid-terrace house: around £650, saving around £140 a year — about 4½ years
Cavity wall insulation
- Mid-floor flat: around £950, saving around £110 a year — about 8½ years
- Mid-terrace house: around £1,100, saving around £110 a year — about 10 years
- Detached house: around £3,900, saving around £380 a year — about 10 years
- Detached bungalow: around £1,700, saving around £160 a year — about 10½ years
- Semi-detached house: around £2,200, saving around £200 a year — about 11 years
The EST’s cavity wall page also says the insulation is likely to pay back in five years or less. Its own current cost and saving figures work out nearer 9–11 years, so we have used the figures. Bigger homes save more each year but cost more to insulate, which is why payback is similar across house types.
For solid walls and floors, the EST gives savings by house type but a cost only for a typical semi-detached house (walls) or a typical suspended floor, so we have not split those out. Detached homes save more — around £500 a year from solid wall insulation and around £85 a year from floor insulation — which shortens payback, but it stays in decades.
Why does loft insulation pay back so quickly?
Because it is cheap to fit and the roof is a big source of heat loss: the EST says an uninsulated home loses around 25% of its heat through the roof. Mineral wool is laid between and then across the joists, with little disruption to the rooms below. The EST recommends 270mm of mineral wool; other materials reach the same performance at different depths. Before you book it, it is worth knowing the options — see this guide to loft insulation materials and how each is fitted — and our own complete guide to loft insulation.
A top-up is a different story. Going from 120mm to 270mm saves only around £13–£35 a year, depending on the house, because most of the benefit came from the first 120mm.
Is cavity wall insulation still worth it at around 10 years?
For most suitable homes, yes — it is one of the larger yearly savings available, and the EST says the work should come with a 25-year guarantee from the Cavity Insulation Guarantee Agency (CIGA) or an independent insurance-backed guarantee. The bigger question is whether your walls are suitable. The EST says cavity wall insulation might not be right if your home is exposed to extreme weather or flooding, is in poor condition, or has a cavity narrower than 50mm, and that brickwork, pointing, roofs and gutters should be repaired first or the insulation could trap damp or fail.
An installer should assess this before filling the walls. If you want to understand what goes wrong when the wrong wall is filled, this explains the problems that can follow cavity wall insulation. Our cavity wall insulation page covers costs and grants.
Why do floor and solid wall insulation take so long?
They are bigger building jobs. The EST bases its solid wall costs on a contractor insulating the whole house in one go and, for internal insulation, fully redecorating afterwards. Suspended floors mean lifting and relaying floorboards; the EST puts a typical suspended floor job at £1,400–£2,500 depending on house type, and says solid floors cost considerably more.
That does not make them a bad idea. The EST points out you can cut costs by timing the work: fit internal insulation when you were going to redecorate anyway, or external insulation when scaffolding is already up for a new roof or windows. The EST also lists reducing draughts as a benefit of floor insulation. If you are lifting floors anyway, read how underfloor insulation goes into suspended timber floors, and keep the air bricks clear: the EST says they ventilate the space under the floor and stop the boards rotting.
Do grants change the ranking?
They can. A grant that covers most of the cost turns even a slow-payback measure into an easy decision. What is available depends on where you live, your income and your home’s energy rating. Our grants guide lists the current schemes in England, Scotland, Wales and Northern Ireland, with official links.
Frequently asked questions
Which insulation pays for itself fastest?
Insulating an empty loft to 270mm: about 4 years for a semi-detached house on EST figures. Draught proofing is close behind at about 4½ years.
How long does cavity wall insulation take to pay back?
About 9 to 11 years depending on house type, dividing the EST’s typical cost by its yearly saving.
Is solid wall insulation worth it?
On bill savings alone it takes roughly 40 to 55 years to repay. It makes more sense with grant funding, when combined with other building work, or if comfort and condensation on cold walls are the main reasons.
Can I add the savings together?
Not exactly. Each EST saving assumes the measure is done on its own. Once one measure has cut your heat loss, the next saves a bit less.
Sources: Energy Saving Trust guides to roof and loft insulation (updated 8 May 2026), cavity wall insulation (updated 8 May 2026), solid wall insulation (updated 18 June 2026), floor insulation (updated 19 May 2026) and draught proofing (updated 20 May 2026). Savings are for gas-heated homes in Great Britain at fuel prices as of July 2026; costs are typical unsubsidised professional prices. Payback figures are our own division of those numbers, rounded. The 0% VAT rate on installed energy-saving materials runs until 31 March 2027 (HMRC VAT Notice 708/6). Checked 2 October 2026.