Home Insulation Costs UK 2026: Room-by-Room Breakdown

Home Insulation Costs UK 2026: Room-by-Room Breakdown

Insulating your home is one of the highest-return investments you can make as a UK homeowner. Heating accounts for roughly 60% of the average energy bill, and a poorly insulated house leaks that heat — through the roof, walls, floors, and gaps around windows and doors. The question is not whether to insulate, but where to start.

This guide breaks down the cost of every major insulation measure, the savings you can realistically expect, and the free funding options available through government schemes in 2026.

Insulation Costs at a Glance

Insulation Type	Typical Cost	Annual Saving	Payback Period	Best For
Cavity wall insulation	£450 – £1,500	£200 – £400	2 – 4 years	Homes built 1920s – 1990s
Loft insulation (DIY)	£300 – £600	£200 – £350	1 – 2 years	All house types with loft access
Loft insulation (professional)	£400 – £1,000	£200 – £350	2 – 4 years	All house types with loft access
Solid wall (internal)	£4,000 – £14,000	£300 – £500	10 – 30 years	Pre-1920s solid-brick homes
Solid wall (external)	£8,000 – £22,000	£300 – £500	20 – 40 years	Pre-1920s solid-brick homes
Floor insulation	£500 – £1,200	£50 – £150	5 – 15 years	Suspended timber floors, ground floor
Draught proofing	£100 – £300	£50 – £100	2 – 4 years	All homes, especially older properties

Savings figures are based on Energy Saving Trust estimates for a gas-heated semi-detached home in England. Results vary depending on property size, current energy tariff, and existing insulation levels.

Cavity Wall Insulation

What Does It Cost?

Cavity wall insulation typically costs between £450 and £1,500, depending on the size of your property. A terraced house may cost £450–£700, a semi-detached £600–£1,000, and a detached house £900–£1,500. Installation takes a single day: a contractor drills small holes in the external brickwork, injects insulation material, and fills the holes.

How Much Does It Save?

The Energy Saving Trust estimates that cavity wall insulation saves a semi-detached household around £200–£400 per year on heating bills. The payback period is typically 2 to 4 years, making it one of the best financial returns in home improvement.

Is It Right for Your Home?

Cavity walls exist in most UK homes built between approximately 1920 and the 1990s. If your house was built after around 1990, it likely already has insulation. If it was built before 1920, it almost certainly has solid walls — a different and more expensive problem. A surveyor or energy assessor can confirm with a quick visual inspection or by checking your EPC.

Cavity wall insulation is not always suitable. It should be avoided if your walls are in a very exposed, wind-driven rain location, if the cavity is too narrow (under 50mm), if there is existing damp, or if the cavity has significant debris or ties in poor condition. A proper pre-installation survey is essential.

Free Grants Available

Under the Great British Insulation Scheme (GBIS), households in council tax bands A–D in England may qualify for fully funded cavity wall insulation. ECO4 funding is available for households receiving certain means-tested benefits. Read our full cavity wall insulation guide for detailed eligibility information.

Loft Insulation

What Does It Cost?

Loft insulation is the single best-value insulation measure for most UK homes. If you are willing to do it yourself, mineral wool rolls cost £300–£600 in materials for a typical semi-detached house. Professional installation, including labour and materials, runs £400–£1,000.

Building regulations now require a minimum of 270mm of loft insulation. Many older UK homes have 100mm or less, meaning there is significant room for improvement even in properties that were insulated decades ago.

How Much Does It Save?

A well-insulated loft can save £200–£350 per year on energy bills. The payback period for a professional install is typically 2–4 years; for DIY it can be under 2 years. No other single measure offers a faster return.

Read our full loft insulation guide for a step-by-step DIY walkthrough and grant eligibility details.

Solid Wall Insulation

What Does It Cost?

Solid wall insulation is the most expensive measure on this list, and that is because it is physically complex. Rather than filling an existing cavity, you are adding an entirely new layer of insulation to the inside or outside of a solid brick wall.

Internal solid wall insulation costs £4,000–£14,000 for a whole house. This involves attaching insulated plasterboard to the interior face of external walls, reducing room size slightly. It can be done one room at a time, which makes it more manageable.

External solid wall insulation costs £8,000–£22,000. Insulation boards are fixed to the exterior of the building and then rendered or clad. This does not affect interior space and can dramatically improve the look of an older property, but it does require planning permission in conservation areas and can face additional complications in flats or terraced rows.

How Much Does It Save?

Both methods save a similar amount — roughly £300–£500 per year on a semi-detached property. The payback period, however, is long: 10–30 years for internal, and 20–40 years for external, without grant funding. This is why solid wall insulation almost always needs to be backed by ECO4 or GBIS funding to make financial sense for most homeowners.

When Is It Worth Doing?

Solid wall insulation makes most sense when you are doing other major renovation work (replastering, reroofing, or re-rendering) or when you are planning a heat pump installation. Insulating before fitting a heat pump reduces the system size needed and lowers running costs significantly.

Floor Insulation

What Does It Cost?

Floor insulation typically applies to ground floors with suspended timber construction — common in pre-1960s UK homes. The cost ranges from £500 to £1,200 for a professional installation, which involves accessing the under-floor void (either from below via a crawl space, or by lifting floorboards) and fitting rigid or flexible insulation between and beneath the joists.

Solid concrete ground floors can also be insulated, but this is a much bigger job that involves raising the floor level and is usually only done during full renovation works.

How Much Does It Save?

Floor insulation saves around £50–£150 per year — less than loft or wall measures. Heat rises, which is why roof and wall losses tend to be larger. However, a cold floor is a significant comfort issue in older homes, and floor insulation can make a noticeable difference to how a room feels.

Draught Proofing

What Does It Cost?

Draught proofing is the cheapest measure on this list: £100–£300 for a professional to seal gaps around windows, doors, skirting boards, loft hatches, and pipework. DIY materials can be purchased for under £50. It is also one of the quickest jobs to complete.

How Much Does It Save?

The Energy Saving Trust estimates draught proofing can save £50–£100 per year. The payback period for a professional job is 2–4 years; for DIY it can be under a year. More importantly, it has an immediate impact on comfort — draughts are one of the primary reasons older homes feel cold even when the heating is on. See our best draught proofing products guide for the specific products we recommend, including our dedicated door draught excluder guide.

Note: Draught proofing should not be confused with ventilation. Every home needs some fresh air. Do not seal ventilation bricks, air vents in rooms with gas appliances, or trickle vents in windows without first ensuring there is adequate air circulation. Seek professional advice if in doubt.

Which Insulation Should You Prioritise?

The answer depends on your house type and what you already have. Here is a practical priority order for most UK homeowners:

For Houses Built Between 1920 and 1990 (Cavity Walls)

1. Loft insulation — if you have less than 270mm, top it up first. Fastest payback, easiest to do.
2. Cavity wall insulation — if not already done, a 2–4 year payback makes this essential.
3. Draught proofing — low cost, immediate comfort benefit.
4. Floor insulation — if you have a suspended timber ground floor and draughts underneath.

For Houses Built Before 1920 (Solid Walls)

1. Loft insulation — same as above; always the first step.
2. Draught proofing — older homes typically have more gaps and cracks.
3. Solid wall insulation — only if you can access grant funding or are doing broader renovation works.
4. Floor insulation — especially if you have original suspended floors.

For Houses Built After 1990

These homes should already have cavity wall and loft insulation, though both may need topping up if you have not checked recently. Focus on draught proofing, floor insulation, and checking whether your existing loft insulation meets the 270mm standard.

For all house types, don't overlook cheap wins like pipe insulation in your loft and garage, and thermal curtains if you have single-glazed or draughty windows.

Free Insulation: GBIS and ECO4 in 2026

Two main government schemes fund insulation for eligible homeowners in England:

Great British Insulation Scheme (GBIS)

GBIS is available to homeowners and private renters with an EPC rating of D or below who live in a property in council tax band A–D. Eligible households can receive fully-funded insulation — most commonly loft and cavity wall — at no cost. The scheme runs until March 2026, though extensions are possible.

ECO4

ECO4 (Energy Company Obligation, phase 4) is targeted at lower-income households receiving qualifying benefits, including Universal Credit, Pension Credit, Child Tax Credit, and others. It funds a broader range of measures, including solid wall insulation and heat pumps, not just the cheaper options. ECO4 funding is delivered through energy suppliers and approved installers — check eligibility via the Energy Saving Trust or your energy supplier. If you're also considering a heat pump, the Boiler Upgrade Scheme provides a separate £7,500 grant on top of any insulation funding.

Scotland and Wales

Scotland operates its own Home Energy Scotland scheme, which offers free advice, cashback grants, and interest-free loans for insulation measures. Wales has the Nest scheme, which provides free energy efficiency improvements to eligible households. Both schemes have separate eligibility criteria.

Insulation and Heat Pumps: Why Order Matters

If you are considering a heat pump in the future, the order in which you make improvements matters significantly. Heat pumps are sized based on your home's heat loss — the better your insulation, the smaller and cheaper the heat pump you need, and the lower your running costs will be. Read our guide on whether to insulate before getting a heat pump to understand the full picture before committing to either measure.

Summary

For most UK homeowners, the right order is: loft insulation first, then cavity wall if applicable, then draught proofing, then floors. Use our insulation savings calculator to estimate how much each measure could save you. Solid wall insulation is almost always a grant-dependent decision. If you qualify for GBIS or ECO4, prioritise those applications — the cost of fully-funded insulation is zero, and the savings begin immediately.