COST GUIDES
How much does retrofit insulation cost in 2026?
Updated 07/26
How much does retrofit insulation cost? Find prices for cavity wall, solid wall, loft, and floor insulation, plus which government grants you could claim.
Fast Facts
Cavity wall insulation (semi-detached house): £2,500-£3,000
Spray foam roof insulation (semi-detached house): £3,000-£4,000
Solid floor insulation (semi-detached house): £2,000-£4,000
According to the Energy Saving Trust, in an uninsulated home, about 33% of heat loss is through the walls, and around 25% escapes through the roof.
If your heating is on full blast during the winter but your home still feels cold, it might be time to upgrade your insulation. Retrofitting insulation can:
Save money on your heating costs
Improve your home comfort
Make your home more environmentally friendly
Here, you'll find all you need to know about average retrofit insulation costs across the walls, roof, and floor, including the potential cost savings of installation and the additional costs to be aware of.
You may also be able to reduce the cost through a government grant scheme: we cover the main options below. If you're managing a larger project, it's worth looking into retrofit coordinator cost too, as a coordinator can oversee the whole programme of work.
How much does retrofit insulation cost?
| Item | Cost range (for a semi-detached house) |
|---|---|
| Retrofit cavity wall insulation | £2,500-£3,000 |
| Retrofit solid wall (internal) insulation | £8,000-£10,000 |
| Retrofit external wall insulation | £10,000-£12,500 |
| Retrofit loft insulation - rolls | £600-£1,000 |
| Retrofit roof insulation - spray foam | £3,000-£4,000 |
| Retrofit floor insulation – suspended | £1,500-£3,000 |
| Retrofit floor insulation – solid floor | £2,000-£4,000 |
| Last updated: July 2026 Our costs are ballpark averages - get a local tradesperson to quote now | |
The cost ranges in the table provide a guide as to what you can expect to pay for retrofit insulation (low–high) in a semi-detached house.
Costs will vary depending on several factors. Contact certified insulation installers covering your local area to get a quote for your property.
Eligible homeowners may be able to get insulation funded through government schemes. See our grants section below.
Retrofit wall insulation cost
Wall insulation helps retain heat in winter and keeps homes cooler in summer.
The method of insulation you choose depends on whether you have cavity walls or solid walls.
How much does cavity wall insulation cost?
Cavity walls (common in homes built between 1920 up to around the mid-80s) can be insulated by injecting insulating material into the space between the bricks, i.e. 'the cavity'.
Cost: Cavity wall insulation costs between £2,500-£3,000 for a small, semi-detached house
Savings: The Energy Saving Trust estimates annual savings of around £240 with cavity wall insulation installed (in a semi-detached home)
Pros: Cavity wall insulation is cost-effective and can be installed relatively quickly
Cons: Not suitable for all homes; a surveyor can inspect your walls to be sure
If you're eligible for ECO4, cavity wall insulation is one of the measures that can be funded at no cost to you. See the grants section below for details.
For a dedicated breakdown, see our cavity wall insulation cost guide. If you've had cavity wall insulation before and it's failed, check our guide to cavity wall insulation removal cost.
How much does solid wall insulation cost? (internal and external)
Solid walls (more common in older homes) can be insulated either internally or externally.
Cost: Internal wall insulation costs between £8,000-£10,000; External wall insulation costs between £10,000-£12,500
Savings: The Energy Saving Trust estimates annual savings of around £320 with solid wall insulation installed (in a semi-detached home)
Pros: High potential savings on your energy bills
Cons: High cost. External wall insulation may need planning permission in conservation areas or on listed buildings
Retrofitting wall insulation may require you to upgrade your home's ventilation to prevent damp issues. Always work with a certified installer, who can offer the necessary guidance.
What is internal wall insulation?
Internal wall insulation uses rigid insulation boards fixed to the inner face of your external walls.
It works on both solid brick walls and cavity walls, making it one of the most flexible options for older homes.
The trade-off is a small reduction in room size, as the boards take up space on the internal face of the wall.
If you're considering it, get an EPC assessment first. See our guide to how much an EPC costs to understand where your home currently sits.
Find an EPC assessor near me
Find an EPC assessor near you in the UK with Checkatrade. Compare quotes, read reviews, and book checked tradespeople to arrange an Energy Performance Certificate for selling, renting, or improving your property’s energy efficiency.
Retrofit loft insulation cost
Loft insulation is arguably the easiest kind to fit retrospectively, especially if you insulate at the joists.
How much does loft insulation cost?
Loft insulation cost (joists): Expect to pay between £600-£1,000 (providing you have easy access to your loft)
Roof insulation cost (rafters): Costs normally sit between £3,000-£4,000 (spray foam insulation sits at the higher end of this price scale)
Savings: The Energy Saving Trust estimates annual savings of around £230 with loft insulation installed (in a semi-detached home)
Pros: Quick to install and significant heat retention; good in irregular or hard-to-reach areas
Cons: Spray foam insulation can cause ventilation issues and damp if not installed correctly, which can impact mortgage eligibility
Loft insulation is one of the most affordable options to retrofit. It's also the type most likely to qualify for grant funding.
Find an expert to retrofit insulation
Retrofit floor insulation cost
Floor insulation helps to reduce draughts and retain warmth. If you're tired of feeling icy cold floors beneath your feet in the winter, this one's for you.
The method of insulation you choose depends on whether you have suspended timber floors (cavity floors) or solid, concrete floors.
How much does suspended timber floor insulation cost?
If you have suspended floors, you might experience cold air rising between your floorboards.
To prevent this, the floorboards can be removed, and the space beneath them can be filled with insulating materials.
Cost: Suspended floor insulation tends to cost between £1,500-£3,000 per ground floor
Savings: The Energy Saving Trust estimates annual savings of around £55 with insulation installed under the floorboards on the ground floor (in a semi-detached home)
Additional costs: If the price doesn't include the removal and replacement of the floorboards, you'll need a carpenter to handle this for you. Carpenters tend to charge between £30-£45 per hour
There are several insulating materials, each with its pros and cons. Whichever type you select, choose installation by a checked installer to avoid issues with damp. Good sub-floor ventilation is also worth budgeting for, as it prevents moisture build-up beneath the boards.
Contact a certified insulation installer covering your local area for guidance on the optimal solution for your home.
How much does solid floor insulation cost?
Lots of new homes are built with solid floor bases made from concrete or screed. However, you can still add insulation if you want to make your floor feel warmer underfoot.
Cost: You can expect to pay between £2,000-£4,000 for solid floor insulation
Additional costs: Adding floor insulation to a concrete or screed floor will increase the total floor depth. You may need to budget for adjustments to doorways and thresholds, plus new skirting boards. Expect to pay between £30-£45 per hour for this type of work
Floor insulation must be installed in accordance with current building regulations.
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Can I get help paying for retrofit insulation?
Several government schemes can reduce or cover the cost of retrofit insulation for eligible households.
ECO4 (Energy Company Obligation 4)
ECO4 is a government scheme that requires energy suppliers to fund energy efficiency improvements (including insulation) for low-income and vulnerable households.
If you receive certain benefits or have a low EPC rating, you may qualify. Contact your energy supplier or check via the gov.uk eligibility checker.
The Warm Homes Local Grant
This scheme targets owner-occupiers and private renters in England with an EPC rating of D or below and a household income under £36,000.
It can fund wall, loft, and floor insulation, among other improvements.
Local councils administer the grants: check with your local authority.
Our guide to current green home improvement grants offers the full picture.
Key takeaways
The cost of retrofitting insulation will vary based on the method and materials you choose and the size of your home
Retrofitting insulation can significantly reduce energy bills
Ventilation upgrades may be necessary to prevent damp
Retrofitting insulation could require some superficial work, e.g. to skirting, doors, and thresholds
Government grants may cover part or all of the cost if you're eligible
Remember that small fixes like draught proofing can also help to improve your home's efficiency
Finding insulation installers near you
Finding insulation installers is easy with Checkatrade.
We check, verify and approve all of our members. All of the tradespeople in our directory meet our high quality standards.
Compare quotes from insulation installers we've checked and reviewed. Simply search your postcode to get started.
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Retrofit insulation cost checklist
FAQs
Two of the most affordable types of insulation to retrofit are loft insulation and cavity wall insulation. Loft insulation at joists typically costs £600–£1,000 for a standard semi-detached and can be installed in a day.
Energy efficient homes are more attractive to potential buyers and therefore can help to increase property value. According to the Government's Department of Energy and Climate Change (DECC), making energy-saving improvements to your home increases the value by 14% on average — and up to 38% in some parts of England.
Yes. Government schemes such as ECO4 and the Warm Homes Local Grant offer financial help to eligible homes. Each scheme has different eligibility criteria.
For most homes, yes. Insulation reduces heat loss, which cuts energy bills. The Energy Saving Trust estimates cavity wall insulation saves around £240 a year; loft insulation saves around £230. Even with installation costs, payback periods are typically 2–5 years. Homes with better EPC ratings also tend to sell faster and at higher prices.
Internal wall insulation doesn't usually need planning permission. External wall insulation may need it if your home is in a conservation area, is a listed building, or if the new cladding changes the appearance of the property significantly. Always check with your local planning authority before starting work.
Lifespan varies by type. Cavity wall insulation typically lasts 25 years or more. Loft insulation (mineral wool) can last 40+ years if kept dry. Floor insulation lifespan depends on the material used — rigid boards under solid floors can last the lifetime of the building. Always use a certified installer to ensure the job is done correctly.
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