Insulation cost & savings estimator
Insulation is usually the cheapest energy upgrade you can buy — and the fastest to pay back. Enter your house type and what you want done for costs, annual savings and payback.
Figures checked October 2026 Estimate
Savings estimated at October 2026 price-cap gas prices (7.97p/kWh) for a gas-heated home starting from little or no insulation. Homes on electric heating save more per unit of heat kept in.
Insulation costs and savings in 2026
Loft insulation is the best-value upgrade in most UK homes: topping up to the recommended 270mm costs an estimated £300–£600 professionally installed (less as a DIY job with rolls from a builders’ merchant) and saves an estimated £110–£340 a year depending on house type — a payback often inside two winters. Cavity wall insulation costs more, an estimated £1,000–£2,700, because it’s a specialist injected job, but it attacks the biggest heat-loss surface in the house and saves an estimated £140–£460 a year.
The savings figures above assume you’re starting from little or no insulation — the classic pre-1990s loft with 50mm of tired insulation, or empty cavities. If your loft already has 150mm+, topping up still helps but the savings roughly halve, which is why the calculator shows a payback range rather than a promise. Detached homes save most in absolute terms (four exposed walls, big roof), flats least (neighbours above, below and beside are doing some of the work).
Before you pay for it yourself
Check the grant checker first: ECO4 (until 31 December 2026) and the Warm Homes: Local Grant (to March 2028) can fund insulation for eligible households, and local energy-advice schemes sometimes subsidise cavity work. Also worth knowing: insulation raises your EPC band — often by a full letter — which matters if you’re selling, remortgaging on a green deal, or a landlord facing the EPC C requirement. See what it does to your band in the EPC estimator.
Insulation questions
How thick should loft insulation be?
The recommended depth is 270mm for mineral wool. Many older lofts have 100mm or less. The jump from 0 to 270mm saves the most; 100mm to 270mm still saves a useful amount.
Can every home have cavity wall insulation?
No. You need cavity walls (mostly post-1930s construction) in reasonable condition, and exposed, driving-rain-prone walls in the west may need extra care. A reputable installer surveys first and will say no if it’s unsuitable — walk away from one who won’t.
Does insulation make the house too hot in summer?
The opposite, generally: loft insulation also slows heat coming in through the roof on hot days. Ventilation still matters — insulation without airflow control can cause condensation, which a good installer designs around.
Ready for real prices?
Calculators give you the ballpark. Get free, no-obligation quotes from MCS-certified UK installers and compare them against these numbers.