Insulation Savings Calculator

What Insulation Saves, Measured

DESNZ's National Energy Efficiency Data-Framework (NEED) compares the gas use of homes in England and Wales that had a measure installed mid-May 2023 to mid-May 2024 with similar homes that didn't. The median first-year savings across all homes:

DESNZ says there's generally no sign of systematic differences in savings between types of home, so the calculator applies these percentages to your house type's median gas use rather than using its by-type figures, which swing with small samples. The spread is wide: for each measure the lower quartile is a rise, so in at least a quarter of homes gas use went up against the comparison group. DESNZ gives two reasons the figure can understate the effect: some comparison homes may have had work done that isn't recorded, and households may heat a warmer home to a higher temperature (comfort taking). The loft figure covers every loft job, top-ups included; the Energy Saving Trust puts a top-up from 120mm at about £17 a year. These are England and Wales figures; DESNZ's Scottish tables don't cover insulation.

The Cheap Wins

• Hot water cylinder jacket: about £30; an 80mm jacket over a cylinder with 25mm of foam saves about £45 a year (Energy Saving Trust). Pays back inside a year.
• Draught proofing: about £250 to have windows and doors done professionally; the Energy Saving Trust puts the saving from windows, floors and doors at about £55 a year. Doing it yourself is cheaper.
• An unused chimney: a cap from about £150, saving about £45 a year (Energy Saving Trust).

The Big Measures

• Cavity wall insulation: £2,200 for a typical home (Energy Saving Trust), about £101 a year for a median semi, so about 22 years.
• Loft insulation: £600 to top up or £750 for a bare loft (Energy Saving Trust, Great Britain). Our view: a bare loft is where the money is; a top-up mostly buys comfort.
• Solid wall insulation: £12,000 internal to £15,000 external for a semi, saving about £146 a year: about 82 years at the internal price, so it needs a grant to make sense on money alone.
• Floor insulation (suspended timber): £1,400 to £2,500, about £55 a year, so about 35 years at the middle of the range.
• A-rated double glazing replacing single: about £4,800 for a semi, about £85 a year: about 56 years. On money alone it doesn't add up.

These are Great Britain figures. In Northern Ireland the Energy Saving Trust's costs are different (cavity fill around £1,000, a bare loft £1,100) and Ofgem's price cap doesn't apply.

Grants That Can Cover the Cost

• ECO4 (England, Scotland and Wales, until 31 December 2026): through energy suppliers for households on certain benefits, with homes rated D to G if you own them, E to G if you rent privately (with the owner's permission), and social housing rated E to G.
• Warm Homes: Local Grant (England): homes rated D to G with a household income usually of £36,000 or less, where your council has funding.
• Scotland: Home Energy Scotland grants for homeowners of up to £1,500 for loft, cavity or underfloor insulation and up to £7,500 for solid walls, within up to 75% of the cost, with an optional interest-free loan.
• Wales: Nest offers free improvements to eligible households.
• Northern Ireland: NISEP gives free insulation for household incomes under £33,000 (single) or £40,000 (couple), and 40% off up to £650 a measure at any income; Affordable Warmth helps households under £23,000.

See England, Scotland, Wales and Northern Ireland for the details.

The Order We'd Do It In

Our view: do the cheap wins first, because they pay back quickly. Then fill empty cavities and insulate a bare loft, which do the most per pound of the bigger jobs, especially if a grant covers them. Leave glazing and solid walls until there's a grant, or a reason beyond the bill. If a heat pump is coming, do the insulation before the heat loss survey, so the heat pump is sized for the house you'll have; our EPC calculator shows what each measure does to the rating.