Home Insulation: The Complete UK Guide
Cavity wall, loft, solid wall, and floor insulation guides: costs, grants, and DIY options for UK homes.
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If you only do one thing before a heat pump or solar install, insulate first. It's the highest-ROI energy upgrade most UK homes can make: less heat lost out of the walls and roof means a smaller heat pump, lower running costs, and a warmer house from day one.
Around 25 million UK homes could be better insulated, and ECO4 or the Great British Insulation Scheme will fund up to 100% of the work for eligible households. Even if you pay full price, loft and cavity wall insulation typically pay back inside 3-5 years.
Bottom line
For nearly every UK home, insulation is the highest-ROI energy upgrade you can make.
Loft insulation pays back in 2-4 years, cavity wall in 3-5, and ECO4 or GBIS may cover both in full if you qualify, so check the grants before you pay anything. The hard case is solid-wall homes: external or internal insulation costs £8,000-18,000 fitted and rarely pays back inside a decade without a grant. Exposed coastal walls and listed buildings need extra care too.
Insulation measures at a glance
Typical UK figures for 2026. Highlighted row is the "start here" pick for most homes.
| Measure | Cost | Annual saving | Payback |
|---|---|---|---|
| Loft top-up (to 270mm) | £400-800 | £150-250 | 2-4 yrs |
| Cavity wall fill | £450-1,500 | £150-300 | 3-5 yrs |
| Draught proofing | £100-300 | £30-60 | 2-5 yrs |
| Solid wall (internal) | £8,000-15,000 | £300-500 | 20-25 yrs |
| Solid wall (external) | £10,000-18,000 | £300-500 | 25-30 yrs |
Understand
Work out which measures pay back fastest for your home
Insulation is a portfolio choice rather than a single big install. Start by costing the options for your house and running the calculator to see which ones pay back fastest, with grants factored in.
GuideWhat insulation costs in 2026 (and what it saves)
The full price-and-payback table for every measure: loft, cavity, solid wall, floor, draught proofing. Sorted by cost-per-pound-of-saving so you know where to start.
Read guideInsulation savings calculator
Compare 6 insulation measures side-by-side for your house. Costs, annual savings, payback, ECO4 / GBIS eligibility and the right order to do them in.
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Plan
The two big paid measures
If you can do nothing else, do these two. Cavity wall and loft insulation are the highest-impact paid jobs, both often grant-funded, and both with payback well inside a decade even at full price.
GuideCavity wall insulation: the 3-year payback measure
Most homes built between the 1930s and 1990s have unfilled cavities. £450-1,500 to fill, £150-300 a year saved, often free under ECO4 or GBIS. The main exception is exposed coastal walls.
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GuideLoft insulation: top up to 270mm
Most UK lofts have 100mm of old fibreglass. Topping to the recommended 270mm costs £400-800, saves £150-250 a year, and is a straightforward DIY job if you can move the boards.
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DIY quick wins (and what's worth buying)
A weekend of draught proofing and pipe lagging will often save more than a smart thermostat. Here are the products we'd actually buy, the ones we wouldn't, and how to know which is which.
GuideBest loft insulation materials
Mineral wool vs sheep's wool vs PIR boards: which to use where, what thickness you actually need, and the brands worth buying. With realistic prices and DIY notes.
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GuideBest draught proofing products
The single highest-ROI weekend job in the house. £100-300 of brushes, strips, foam and chimney balloons can knock £30-60 a year off your bill and pay back inside a year.
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