How Much Does Home Insulation Cost in the UK?

Home insulation costs anywhere from around £300 for a simple loft top-up to £22,000 or more for a full external wall wrap on a detached house. Most single-measure jobs fall well short of that upper figure, and which end you land on depends almost entirely on what you're insulating and how the house was built. This guide breaks down loft, cavity wall, solid wall, and underfloor insulation costs one by one, with the typical saving and payback for each, so you can work out which is actually worth doing.

Quick cost summary

Here is how the main insulation types compare on cost, typical saving, and payback time, drawn from Energy Saving Trust, Which?, and Checkatrade data (sources given in each section below).

Insulation is also one of the cheapest ways to shift your EPC rating, which matters if you're selling, remortgaging, or renting the property out.

Loft insulation cost

Loft insulation is the cheapest, fastest-paying-back measure on this list, which is why it's usually the first job recommended for any home. There are two different jobs hiding under one name, and the price depends on which one you need.

Topping up existing insulation

If your loft already has insulation but it's thin (old properties often have 50-100mm rather than the recommended 270mm), topping it up costs £300 to £600 for a whole loft on most house sizes. The saving is smaller than a full install since you're adding to what's already there, but payback is still under two years, the fastest of any home improvement on this list. Expect roughly £125-£220 a year off bills in a smaller home or flat, rising to £350 or more for a larger detached house, on Energy Saving Trust-derived estimates.

Full install where there's none currently

If there's no insulation at all, a full install to 270mm costs £400 to £1,200 for a whole loft: around £200-£500 for a flat or one-bed, up to £900-£1,800 for a four-bed detached house. Savings run higher too, typically £220-£355 a year for a terrace or semi and up to £355-£580 a year for a detached house. Payback is around 2 to 2.5 years.

Loft insulation is genuinely DIY-friendly if you can access the joists comfortably; a competent DIYer can lay mineral wool rolls in a weekend for materials cost alone. A converted loft or room-in-the-roof is a different, more involved job, costing roughly £1,100-£2,250 for a typical ~50m² conversion. We'd flag that figure as lower confidence than the numbers above, since it comes from a trade-pricing aggregator rather than Energy Saving Trust, Which?, or Checkatrade directly.

Cavity wall insulation cost

Houses built after around 1920 typically have cavity walls: two skins of brick or block with a gap between them, which can be filled with insulation through small drilled holes from outside without disturbing anything indoors. It's one of the best value measures available, second only to loft insulation on payback.

These are Checkatrade's typical figures per house type, so treat them as a midpoint rather than a quote: real prices move with wall area, access, and whether old failed cavity fill has to be cleared out first. Even so, payback lands under 5 years for every house type, which is quick for a measure that sounds disruptive but usually isn't: it's done from outside in a day.

Not every cavity is suitable. Walls exposed to driving rain, cavities under 50mm wide, and some non-standard construction types need a survey first to confirm the fill won't cause damp. A reputable installer always surveys before quoting.

Solid wall insulation cost: internal

Houses built before around 1920, and some later system-built properties, typically have solid walls with no cavity to fill. Internal insulation (dry-lining) is usually the cheaper of the two solid-wall options, though "cheaper" is relative: expect £5,000 to £15,000 for a whole house, with the Energy Saving Trust citing a typical figure of around £12,000 for a 3-bed semi.

The work involves fixing insulated plasterboard or a stud-and-insulation system to the inside face of every external wall, then re-skimming and redecorating. Every room loses a little floor space and needs sockets refitted, and you'll need a plasterer once the boards are up. It's disruptive enough that most people do it room by room or fold it into other renovation work.

Savings scale with house size: around £180 a year for a flat, up to roughly £540-£660 for a semi and £930 for a detached house. At full retail cost with no grant support, payback is commonly 10 years or more, a much longer horizon than loft or cavity work.

Solid wall insulation cost: external

External wall insulation wraps the outside of the house in an insulated render system instead, leaving the inside untouched. It costs more, typically £8,000 to £22,000 for a whole house, with the Energy Saving Trust's typical figure around £18,000 for a 3-bed semi; smaller mid-terrace jobs can start from around £6,000, larger detached houses run to £20,000 or more.

Because it changes the appearance of the house and thickens the walls, it's a bigger structural job than internal dry-lining, and it's worth involving a builder early to check guttering, pipework, and boundary distances. Properties in conservation areas or with listed status may also need planning permission, which internal work doesn't.

Savings are the same order as internal insulation, roughly £180-£930 a year depending on size. Payback at full retail price is long, often 15 to 20 years or more without grant support, which is why this measure is one of the ones most commonly targeted by government funding rather than done at full cost.

Underfloor insulation cost

Ground floor insulation is the least talked-about measure but can noticeably improve comfort in older houses with suspended timber floors that let cold air circulate underneath.

For a suspended timber floor, insulation is fitted between the joists from below or by lifting boards from above, costing £1,500 to £3,000 for a whole ground floor, with the top of the range covering jobs where floorboards need lifting and relaying. A solid concrete floor usually needs insulation laid on top as a new floating floor build-up instead, typically £2,000 to £4,000.

Unlike the measures above, we could not find a reliable, consistently published saving or payback figure for underfloor insulation from Energy Saving Trust, Which?, or Checkatrade. Floor heat loss is real but smaller than wall or roof heat loss in most houses, so treat this as a comfort upgrade first and a bill-saving measure second.

Which insulation is worth doing first

If you can only do one thing this year, do the loft. A top-up pays back in under two years, a full install in around 2 to 2.5 years, faster than anything else here, and the job itself is quick and low-disruption.

After that, if your house has cavity walls, do that next: under 5 years payback across every house type, done from outside in a day. Between a loft top-up and cavity fill, most homes can meaningfully cut their heating bill for well under £2,500 combined.

Solid wall insulation is a different calculation. At full retail price, payback stretches to 10-20+ years, so it rarely makes sense as a standalone project purely for the energy saving. It tends to get done because the house needs re-rendering anyway, it's bundled into a larger renovation, or it's funded through one of the grant schemes below. Underfloor insulation sits lowest priority simply because there isn't a reliable figure to rank it against; it's sensible to do opportunistically, for example while floorboards are already up for other work.

Whatever you insulate, do it before upgrading the heating system. A new boiler sized for a leaky house is oversized once that house is insulated, and a heat pump performs far better, and can often be sized smaller and cheaper, in a well-insulated home.

Grants and funding for insulation

Funding in this space changes often, so check current eligibility directly rather than relying on anything you read a year or two ago. Here's the position as things stand.

ECO4 is still running. It requires large energy suppliers to fund insulation and heating measures for low-income and vulnerable households, with eligibility usually through qualifying benefits or a local authority's flexible eligibility route, and typically requires an EPC rating of D to G. It was due to close at the end of March 2026, but the government confirmed a nine-month extension, so it now runs to the end of December 2026.

The Great British Insulation Scheme (GBIS), which ran alongside ECO4, has closed. Its end date was fixed for 31 March 2026 and the government confirmed it wouldn't be extended or reissued, so any older articles pointing to GBIS as a live route to free insulation are now out of date.

In its place sits the Warm Homes Plan, a new umbrella programme covering several billion pounds of funding over five years to upgrade an estimated 5 million homes by 2030. The scheme most homeowners will interact with under that umbrella is the Warm Homes: Local Grant, administered through local councils in England: household income up to £36,000 (or an equivalent low-income route), a privately owned or rented home, and an EPC rating of D to G gets you up to £15,000 for insulation, draught-proofing, glazing or solar, plus up to a further £15,000 for low-carbon heating such as a heat pump, at no cost to the occupant.

Scotland and Wales run their own separate devolved schemes, not covered by the figures above; check your national government's energy efficiency programme directly rather than assuming the English rules apply.

Improving insulation is also one of the quickest ways to move your property up an EPC band. See our EPC improvement cost guide for how insulation compares with other rating improvements.

How to not get ripped off

Insulation is exactly the kind of job where a very cheap quote should make you more cautious, not less. Poorly fitted cavity wall insulation in particular can trap damp rather than solve it, and a botched job can be far more expensive to put right than it was to install.

• Check for TrustMark registration. The government-endorsed quality scheme, and a requirement for any installer delivering work under ECO4 or the Warm Homes: Local Grant.
• Ask about PAS 2035. The government standard for how retrofit insulation projects should be assessed, designed, and installed, including a proper survey before work starts. Any grant-funded work must follow it.
• A fair quote includes a proper survey. For cavity or solid wall insulation especially, a surveyor should check construction, exposure, and condition before quoting a firm price. Be wary of a fixed price given over the phone without anyone seeing the property.
• Get more than one quote. Prices for the same job on the same house type vary hugely between installers, as the tables above show.
• The cheapest quote often isn't the best deal. A low quote can mean thinner insulation than specified or corners cut on preparation. Reputable installers offer a minimum 25-year guarantee on cavity wall insulation, often backed by an industry body like CIGA.
• Get it in writing. The quote should specify the exact material and thickness being installed, not just "insulation", plus the guarantee terms and who's providing them.

If you're planning solid wall or underfloor work alongside other renovation, it's often worth pricing it as part of a wider job with a builder rather than as a standalone insulation contract. Builders in Manchester and Leeds, for example, regularly quote solid wall insulation as part of larger refurbishment projects rather than as a separate trade.

Frequently asked questions

Is loft insulation still worth doing if I already have some?

Almost always, if what's there is thinner than the recommended 270mm. Topping it up costs £300-£600 with payback in under two years, one of the best value jobs available on any house.

How do I know if my walls are cavity or solid?

Check the brickwork pattern. Cavity walls usually show bricks laid lengthways (stretcher bond); solid walls, common before around 1920, mix lengthways and end-on bricks because the wall is a single thickness. A surveyor can confirm if you're unsure.

Can I get free insulation right now?

Potentially, through ECO4 (running until the end of December 2026) if you receive qualifying benefits or meet a flexible eligibility route, or through the Warm Homes: Local Grant if your household income is under £36,000 and your EPC rating is D to G. The Great British Insulation Scheme has closed.

How long does cavity wall insulation last?

Properly installed, it's expected to last the lifetime of the building. Reputable installers back it with a minimum 25-year guarantee, often insurance-backed through a body like CIGA so it still stands if the original installer stops trading.

Will insulating my walls cause damp?

Correctly installed insulation, matched to a suitable wall through a proper survey, shouldn't. Problems arise when cavity insulation goes into unsuitable walls or is fitted poorly, which is exactly why the pre-installation survey matters.

Do I need planning permission for external wall insulation?

Often not, as it's usually covered under permitted development rights, but conservation areas, listed buildings, and some flats may need permission because it changes the building's external appearance. Check with your local planning authority first.

How much could I realistically save by insulating everything?

It depends on your starting point and house size, but a loft top-up combined with cavity wall insulation (where applicable) is where most of the realistic saving sits, given the fast payback on both. Solid wall and underfloor work add further savings but at a much longer payback.

Should I insulate before or after getting a new boiler or heat pump?

Insulate first where you can. A heat pump works most efficiently, and can often be sized smaller and cheaper, in a well-insulated home, and the same logic applies to right-sizing a replacement boiler.