Loft & Cavity Wall Insulation Payback Calculator
Estimate the installation cost, annual savings and payback period for loft insulation, cavity wall insulation, or both, based on your property and current insulation levels.
Used to scale the typical cost and saving figures below. We don’t adjust separately for detached, semi-detached, terraced or flat — there isn’t a reliable published adjustment for that, so property size is the only scaling factor.
The benchmark savings below are published for a gas-heated home. For other fuels we apply a rough adjustment based on relative unit price, not a separately published Energy Saving Trust figure — treat the gas figure as the more reliable one.
Pre-filled with a typical combined estimate for your selections — overwrite it with a real installer quote for accuracy.
Enter a valid amount (0 or more).
Cumulative Savings Over Time
Installation Cost Breakdown
Estimated Annual Saving by Measure
20-Year Financial Projection
Loft & Cavity Wall Insulation Payback Calculator UK 2026
Our Loft & Cavity Wall Insulation Payback Calculator helps you work out whether topping up your loft insulation, filling your cavity walls, or doing both, is likely to pay for itself — and roughly how long that will take. Enter your property size, current insulation status and heating fuel to get an estimate of installation cost, annual savings, and payback period, based on published Energy Saving Trust benchmark figures.
How Much Does Insulation Cost in the UK in 2026?
Costs vary by property size, existing insulation levels and installer, so always get more than one quote. As a general guide:
| Measure | Typical Installed Cost | Typical Annual Saving |
|---|---|---|
| Loft insulation (topping up to 270mm) | around GBP600 | around GBP17 |
| Loft insulation (installing from none) | around GBP750 | around GBP190 |
| Cavity wall insulation | around GBP2,200 | around GBP200 |
Figures are Energy Saving Trust benchmark estimates for a typical gas-heated, medium-sized (3-bed) semi-detached home in Great Britain, scaled here by property size. Note the large gap between installing loft insulation from scratch and simply topping up an already-part-insulated loft — most of the saving is captured by the first layer, so a top-up alone often has a much longer payback.
How to Use This Calculator
- Choose the measure you’re considering — loft insulation, cavity wall insulation, or both.
- Select your property size — this scales the typical cost and saving figures.
- Tell us your current insulation status — loft depth and whether your walls are cavity or solid.
- Select your heating fuel — the benchmark savings are for gas; other fuels get a rough adjustment.
- Review the suggested installation cost, then replace it with a real installer quote if you have one.
- Click Calculate Payback to see your results.
Are There Still Grants for Insulation in 2026?
The funding picture changed significantly during 2026:
- Great British Insulation Scheme (GBIS): closed to new applications on 31 January 2026, with the scheme ending entirely on 31 March 2026. Ignore any site still promoting it as open.
- ECO4: extended to 31 December 2026. Aimed at households receiving a qualifying benefit (such as Universal Credit, Pension Credit or Child Tax Credit) in a property with an EPC rating of D or below.
- Warm Homes: Local Grant: delivered by local councils in England until March 2028, for households with an income of roughly £36,000 or below, or who qualify via a council tax band or postcode-based route.
Most homeowners will not qualify for a funded route and should budget for the self-funded cost. If you think you might qualify for ECO4 or the Warm Homes: Local Grant, select that option in the calculator for a note pointing you to where to check — the tool does not assume a fixed grant amount, since funding levels vary by supplier, council and property.
Loft vs Cavity Wall Insulation: Which Pays Back Faster?
Which pays back faster depends heavily on your starting point, not just which measure you pick. Installing loft insulation from scratch is usually the fastest payback of any of these measures. Topping up a loft that already has some insulation is cheap, but the saving is small enough that payback can stretch well beyond the loft’s own lifespan. Cavity wall insulation sits in between: a bigger outlay, but a solid, predictable annual saving.
| Factor | Loft: None → 270mm | Loft: Top-up → 270mm | Cavity Wall Insulation |
|---|---|---|---|
| Typical installed cost | ~GBP750 | ~GBP600 | ~GBP2,200 |
| Typical annual saving | ~GBP190 | ~GBP17 | ~GBP200 |
| Typical payback (self-funded) | ~4 years | ~35 years | ~11 years |
| Installation time | Half a day | Half a day | A few hours to a day |
| Guarantee | Manufacturer-backed, 25 years typical | Manufacturer-backed, 25 years typical | CIGA 25-year guarantee |
Figures are Energy Saving Trust benchmarks for a medium-sized, gas-heated semi-detached home in Great Britain, before scaling for property size. The gap between the “none” and “top-up” loft columns is the single most important thing to check before spending money on a top-up alone.
How Do I Know If My Walls Have a Cavity?
Homes built after around 1920 in the UK usually have cavity walls — two layers of brick or block with a gap between them. Solid walls, common in older properties, are a single continuous layer, often visibly thinner (around 22cm) compared to cavity walls (around 27cm or more). If in doubt, a surveyor or insulation installer can confirm your wall type, and can also check the cavity is clear of debris and suitable for insulation before any work starts.
How Thick Should Loft Insulation Be?
UK guidance recommends a minimum of 270mm of mineral wool (or the equivalent in other materials) for loft insulation. Many older homes have only 100–120mm, which was the standard a couple of decades ago. Topping up from 100mm to 270mm delivers a smaller saving than installing insulation where there was previously none, but is usually inexpensive and quick to arrange.
Does Insulation Affect My EPC Rating?
Yes. Loft and cavity wall insulation are among the cheapest ways to improve your Energy Performance Certificate (EPC) band, sometimes by a full band or more. This can matter if you’re selling, letting a property (minimum energy efficiency standards apply to rented homes), or simply want a more accurate record of your home’s efficiency for future grant eligibility.
Can I Install Insulation Myself?
Loft insulation is one of the more DIY-friendly home improvements — laying mineral wool rolls between and over joists is straightforward if your loft is easily accessible and free of damp or structural issues. Cavity wall insulation is a specialist job requiring injection equipment and should always be done by a certified installer, both for safety and so the work is covered by a CIGA, BBA or equivalent guarantee.
Frequently Asked Questions
Is loft or cavity wall insulation better value for money?
It depends heavily on your starting point. Installing loft insulation where there was previously none typically costs around GBP750 and saves around GBP190 a year (Energy Saving Trust benchmark), a payback of roughly four years. Topping up an already part-insulated loft to 270mm costs less overall, around GBP600, but saves much less too – often only around GBP17 a year – because most of the benefit is already being captured by the existing insulation. Cavity wall insulation costs more upfront, around GBP2,200, but can deliver a bigger annual saving, around GBP200, where walls are currently uninsulated. Many households do both together, since installers can often offer a combined price.
How much does loft insulation cost in the UK in 2026?
Cost depends heavily on your starting point. Installing insulation in a loft with none currently typically costs around GBP750 and saves around GBP190 a year, according to Energy Saving Trust benchmarks for a gas-heated semi-detached home. Topping up an already part-insulated loft (around 120-150mm) to the recommended 270mm typically costs around GBP600 but saves only around GBP17 a year, since most of the benefit is already being captured by the existing insulation. DIY materials-only costs can be lower, but professional installation ensures even coverage and avoids leaving cold spots.
How much does cavity wall insulation cost in the UK in 2026?
Cavity wall insulation typically costs around GBP2,200 for a typical semi-detached home and saves around GBP200 a year, according to Energy Saving Trust benchmark figures. Larger detached properties will cost more to insulate and can save more; smaller flats and terraces cost less. Always get a borescope survey first to confirm your cavity is suitable and free of obstructions.
Are there still grants for insulation in 2026?
The Great British Insulation Scheme (GBIS) closed to new applications on 31 January 2026 and ends entirely on 31 March 2026. ECO4 continues until 31 December 2026 for households on qualifying benefits in lower-EPC-band properties. The Warm Homes: Local Grant, delivered by councils, runs until March 2028 for lower-income households. Most homeowners will need to self-fund and should check eligibility directly with an energy supplier or their local council before assuming a grant applies.
How do I know if my walls have a cavity?
Homes built from around 1920 onwards usually have cavity walls, recognisable by their thickness (around 27cm or more) and a stretcher-bond brick pattern (all bricks laid lengthways). Older properties often have solid walls, which are thinner and may show a mix of brick orientations. An installer can confirm this and check the cavity is suitable before quoting.
How thick should loft insulation be?
Current guidance recommends a minimum of 270mm of mineral wool or an equivalent. Many homes still have only 100-150mm from older standards. Topping up to 270mm is usually low-cost and quick, though the saving from a top-up is smaller than installing insulation where there was previously none.
Does insulation affect my EPC rating?
Yes, loft and cavity wall insulation are among the most cost-effective ways to improve an EPC rating, sometimes by a full band. This can be relevant for landlords meeting minimum energy efficiency standards, for anyone planning to sell or remortgage, and for checking eligibility for other grant schemes that use EPC band as a qualifying criterion.
Can I install insulation myself?
Loft insulation is often suitable for a competent DIYer if the loft is easily accessible, though care is needed around electrical cabling, ventilation gaps and any damp issues. Cavity wall insulation requires specialist injection equipment and should be carried out by a certified installer so the work is covered by a recognised guarantee such as CIGA or BBA.