Rates and data last verified 10 July 2026 by the ExpertSure editorial team. Sources are listed in the methodology below the calculator.
Insulation is the rare home improvement where the cheapest measures pay back fastest. Loft insulation can return its cost in under three years in a detached house, while cavity wall insulation typically saves hundreds of pounds every year. This calculator compares installed costs against Energy Saving Trust savings estimates for your house type, using July 2026 fuel prices.
- Loft insulation costs around £900 and saves up to £360 a year - an uninsulated detached loft pays back in about 2.5 years
- Cavity wall insulation runs about £2,700 installed - saving £110 to £380 a year depending on house type
- Solid wall insulation is the big-ticket option - £12,000 internal or £18,000 external on a 3-bed semi, saving up to £500 a year
- You pay 0% VAT until March 2027 - insulation qualifies as an energy-saving material, cutting a fifth off pre-relief prices
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How to Use This Calculator
Choose the insulation measure you are considering and your house type. The calculator shows the typical installed cost, your estimated annual saving, the simple payback period, and the 20-year net benefit. Savings figures come from the Energy Saving Trust’s estimates for a gas-heated home at July 2026 prices.
Which Insulation Saves the Most Money?
Per pound spent, loft insulation wins: filling an uninsulated loft to 270mm costs around £900 and saves £140 to £360 a year depending on house type. Cavity wall insulation is next at roughly £2,700 with savings of £110 to £380 a year. Solid wall insulation saves the most in absolute terms – up to £500 a year – but the £12,000 to £18,000 install cost pushes payback beyond 25 years without grant support. Our home insulation cost guide covers every measure in detail.
One caution on the widely-quoted “£20 a year” loft figure: that applies only to topping up an already-insulated loft from 120mm to 270mm. Going from nothing to 270mm saves seven to eighteen times more. See our dedicated loft insulation cost guide and cavity wall insulation guide for the full breakdowns.
Can You Get a Grant for Insulation in 2026?
Two live routes exist. ECO4 runs until 31 December 2026 for households on means-tested benefits in EPC band D to G homes. The Warm Homes: Local Grant, delivered by English councils until March 2028, covers up to £15,000 of efficiency measures for households earning under roughly £36,000. The Great British Insulation Scheme closed to applications in January 2026, so ignore any site still promoting it. Eligibility details and application routes are in our insulation grants guide, and our external wall insulation guide covers the measure grants most often fund.
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