How much money can you save with loft insulation? For a gas-heated home in Great Britain with an empty loft, fitting 270mm of mineral wool insulation saves around £360 a year in a detached house, £190 a year in a semi-detached house, £140 a year in a mid-terrace house and £350 a year in a detached bungalow. Those are the Energy Saving Trust estimates at July 2026 fuel prices, and they make loft insulation one of the fastest-paying home improvements there is. An empty loft typically pays for itself in about three to five years, then keeps saving money for around 40 years, which is how long the insulation lasts.

The catch is that the saving depends almost entirely on what is already up there. If your loft already has 120mm of insulation, topping it up to 270mm saves only £13 to £35 a year, and the payback stretches into decades. So the honest answer to how much money you can save with loft insulation is that it depends on your starting point, your house type and your heating fuel. This guide works through the figures house by house, shows the payback maths, and explains when the job is a bargain and when it is not worth doing for the money alone.

How much money can you save with loft insulation?

The Energy Saving Trust publishes the clearest figures available, and they are based on a gas-heated home in Great Britain with a professional installation at unsubsidised prices. The table below shows the yearly saving from insulating a completely empty loft up to the recommended 270mm of mineral wool, at fuel prices as of July 2026.

Detached houses and bungalows save the most because they have the largest roof area relative to the rest of the house. A mid-terrace house shares walls with its neighbours, so less heat escapes through the roof in the first place, and the saving is smaller. Even so, £140 a year for a job that costs around £650 is a strong return.

The reason the numbers are this large is that an uninsulated home loses around 25% of its heat through the roof, according to the Energy Saving Trust. Heat rises, and without insulation the loft is effectively a hole in the top of the house. Fitting insulation closes most of that hole in a single day, with no change to how you live in the house.

Two warnings belong with these figures. First, they are estimates, not a promise. Your actual saving depends on your house size, how warm you keep it, and what fuel prices do next. Second, they assume a gas-heated home. If your home is heated by oil or electricity, each unit of heat costs more, so the cash saving from stopping that heat escaping is usually larger. If your home is heated by a heat pump, the saving is smaller in cash terms because the heat itself costs less to produce, but the insulation still cuts the amount of electricity the heat pump uses.

What if your loft already has some insulation?

This is where most people get caught out. Loft insulation has diminishing returns: the first 100mm does most of the work, and each extra layer adds less. If your loft already has around 120mm of insulation, topping it up to 270mm saves far less than starting from nothing.

A top-up that saves £17 a year and costs £600 takes about 35 years to pay for itself on energy savings alone. The insulation lasts around 40 years, so it does eventually pay back, but only just. That does not make topping up a bad idea. It makes it a comfort and carbon decision rather than a money decision. A fully insulated loft keeps bedrooms warmer and steadier, and it cuts carbon emissions even when the cash saving is small. But if your only question is how much money you can save with loft insulation, and you already have 120mm up there, the honest answer is not much.

The practical rule is simple. Measure what you have before you spend anything. If you have nothing, or only a thin layer under 100mm, the job pays for itself in a few years. If you already have 120mm or more, get a quote, do the division yourself, and decide whether comfort and carbon matter enough to justify it.

What does loft insulation cost, and how fast does it pay for itself?

Professional installation of 270mm of mineral wool in an empty loft costs around £650 for a mid-terrace house, £750 for a semi-detached house, £1,100 for a detached house and £1,200 for a detached bungalow, according to the Energy Saving Trust at July 2026 prices. Those are unsubsidised prices, meaning no grant has been deducted, and they include materials and labour.

Payback is the cost divided by the yearly saving. For an empty loft that works out at about three years for a detached house, four years for a semi, four to five years for a mid-terrace, and three to four years for a bungalow. Few home improvements pay back that quickly. A new boiler takes far longer, and double glazing can take decades.

DIY changes the maths further. A roll of mineral wool for a typical loft costs a few hundred pounds in materials, so a confident DIYer can cut the payback to under two years. But DIY is only sensible if the loft is accessible, the joists are sound, and you understand the two classic mistakes: compressing the insulation, which destroys its performance, and blocking ventilation or covering downlights and cables, which creates damp and fire risks. If any of that sounds unfamiliar, pay a professional. The saving from a badly fitted job can be a fraction of the figures above.

One cost that catches people out is loft boarding. If you use the loft for storage, you need raised boarding that sits above the insulation rather than squashing it down. That adds cost, and it is worth pricing in before you commit. Squashing 270mm of insulation down to 100mm under boards throws away most of the saving you just paid for.

What changes the number?

The tables above are averages, and your home will differ. Five things move the saving up or down.

Your heating fuel. The figures assume gas. Oil and direct electric heating cost more per unit of heat, so the same insulation saves more cash in those homes. Heat pump homes save less cash but use less electricity, which matters if you are on a time-of-use tariff.

Your house size. A large detached house with a big roof saves more than a small one. The tables use typical sizes, so a very large loft or a very small one will shift the numbers.

How warm you keep the house. Insulation saves the heat you would otherwise lose, so a household that keeps the thermostat at 21 degrees saves more in cash terms than one that keeps it at 18 degrees. Turning the thermostat down still saves money overall, but it shrinks the insulation saving at the same time, because there is less heat to lose.

How much insulation is already there. This is the biggest factor of all, as the top-up table shows. Going from nothing to 270mm is worth ten times more per year than going from 120mm to 270mm.

Whether you can get it funded. Grants and zero-rate VAT change the payback completely. If the installation costs you nothing, every pound saved is pure gain from day one. The next section covers what is still available.

How to check how much insulation you already have

Before you get quotes, spend five minutes in the loft with a tape measure. The recommended depth for mineral wool is 270mm, which is about a foot. Measure the depth in two or three places, because older installations are often patchy, thin near the eaves and thicker in the middle.

If you find nothing at all, you are in the big-saving group. If you find 100mm or less, you are still in the fast-payback group. If you find 120mm or more, you are in the top-up group, and the money case is weak even though the comfort case still holds.

A few safety notes. Walk only on the joists or on boards, never on the ceiling plaster between joists. Wear gloves, a mask and eye protection, because mineral wool irritates skin and lungs. Do not cover recessed downlights or electrical cables with insulation unless they are rated for it. Leave ventilation paths at the eaves clear, because a sealed loft grows condensation and mould. And if your home was built before 2000 and the material up there looks unusual, grey and fibrous, or damaged, do not disturb it. Get a professional survey first, because some older insulation contains asbestos.

Grants and VAT that change the maths

Two things can cut the cost of loft insulation to little or nothing. The first is a grant, and the second is zero-rate VAT.

On grants, the picture has narrowed in 2026. The Great British Insulation Scheme closed on 31 March 2026, and ECO4, the main energy-company obligation scheme, closes on 31 December 2026. The route that remains open is the Warm Homes: Local Grant, which opened in April 2026 for homeowners in England in homes rated EPC D to G with a household income at or below £36,000 or on qualifying benefits. Councils are writing to eligible households in batches, so a letter about free insulation may already be on its way. Our guide to the Warm Homes Local Grant explains the thresholds in full.

On VAT, the installation of energy-saving materials, including loft insulation, is currently zero rated until 31 March 2027, after which the rate returns to 5%. Budget 2026, delivered on 28 October 2026, confirmed that end date, so there is no extension to wait for. The zero rate applies to the supply and installation together when an installer does the work, and there is no income test or application. On a £750 semi-detached installation the difference between 0% and 5% VAT is about £37, which is small, but on a larger job combining insulation with other measures it adds up.

If you qualify for a grant, the payback question disappears entirely. Free insulation that saves £190 a year is £190 a year from the first bill. If you do not qualify, the zero-rate VAT window gives you a reason to act before the end of March 2027 rather than after it, though the saving from the VAT alone is not a reason to rush a bad quote.

Is loft insulation still the best first step?

For most homes, yes. Loft insulation is usually the cheapest major energy-saving measure, it takes a day to install, it needs no planning permission, and it pays back in three to five years from an empty loft. Cavity wall insulation saves a similar amount per year in many homes but costs more to install. Solid wall insulation saves more in total but costs thousands. Draught proofing is cheaper still, around £25 a year saved for a typical home according to the Energy Saving Trust, but the saving is small because the cost is small.

The one exception is a home that already has a well-insulated loft. Then the best next step is usually elsewhere: cavity wall insulation if the walls are unfilled, draught proofing around windows and doors, or heating controls. Our guide to how thick loft insulation should be explains the depth question in detail, and our regulations guide covers what building control expects when you add or replace insulation.

Loft insulation also does something the money figures miss. It makes the upstairs rooms warmer and less draughty, it evens out temperatures through the house, and it keeps the house cooler in summer by slowing heat coming in through the roof. None of that shows up in the payback table, but it is the part homeowners notice first.

Frequently asked questions

How much money can you save with loft insulation?

For a gas-heated home with an empty loft, the Energy Saving Trust estimates yearly savings of about £360 for a detached house, £190 for a semi-detached house, £140 for a mid-terrace house and £350 for a detached bungalow, at July 2026 fuel prices. If the loft already has 120mm of insulation, topping it up to 270mm saves only £13 to £35 a year.

How long does loft insulation take to pay for itself?

From an empty loft, about three years for a detached house, four years for a semi-detached house, and four to five years for a mid-terrace house, based on Energy Saving Trust installation costs and savings at July 2026 prices. Topping up from 120mm to 270mm takes about 23 to 38 years to pay back on energy savings alone.

Is it worth topping up loft insulation from 120mm to 270mm?

For money alone, usually not. The extra layer saves £13 to £35 a year but costs £500 to £800 to install, so the payback is measured in decades. It is still worth doing for comfort and carbon: a fully insulated loft keeps bedrooms warmer and steadier and cuts emissions, and it also helps if you are aiming for a better EPC rating.

Does loft insulation save money in summer too?

Yes, in a smaller way. Insulation slows heat moving in either direction, so a well-insulated loft keeps the upstairs cooler during hot weather and reduces the need for fans or portable cooling. The big saving is still in winter, when it stops expensive heating escaping through the roof.

Can I get loft insulation free?

Possibly. The Warm Homes: Local Grant covers insulation for eligible homeowners in England in EPC D to G homes with household income at or below £36,000 or on qualifying benefits. ECO4 closes on 31 December 2026 and the Great British Insulation Scheme closed on 31 March 2026, so the Warm Homes grant is the main route left. Check eligibility before paying for anything.

How thick should loft insulation be?

The recommended depth for mineral wool is 270mm, which is about a foot. That is usually laid as 100mm between the joists and 170mm across them. Other materials need different depths to reach the same performance, so follow the manufacturer’s guidance for the product you use.

Related reading

• How Thick Should Loft Insulation Be?
• Is There a Free Grant for Installing Loft Insulation?
• What Are the Loft Insulation Regulations for 2026?
• How to Insulate a 100 Year Old House
• New EPC Ratings 2027 Explained

Sources

• Which? Loft insulation costs and savings (Energy Saving Trust data, July 2026 fuel prices)
• Centre for Sustainable Energy, Loft insulation advice leaflet (Energy Saving Trust figures, updated November 2026)
• Energy Saving Trust, Home insulation
• Federation of Master Builders, How do you insulate a loft?
• HMRC, VAT rates applying to qualifying energy-saving materials
• Retro Haus Energy, Energy grants for homes (ECO4 and Great British Insulation Scheme dates)