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Insulation and draught-proofing — cheapest heat you’ll ever buy

The pecking order of home insulation by payback time, typical UK costs, and the £50 fixes that outperform the £15,000 ones.

Efficiency first, gadgets second

Around a quarter of a typical home’s heat leaves through the roof, a third through the walls, and a steady trickle through gaps, floors and windows. Before pricing up heat pumps or solar panels, shrink the amount of heat the house needs — every kilowatt-hour you don’t lose is one you never pay to generate, at any tariff, forever. Insulation is also the rare home improvement with genuinely calculable returns, and the pecking order below is sorted by payback, not glamour.

The pecking order

1. Draught-proofing — pounds, not thousands. Self-adhesive strips around doors and windows, a letterbox brush, a chimney balloon or damper for unused flues, sealant along skirting gaps: perhaps £50–£250 DIY for the lot, saving £50–£100+ a year in a draughty house, with instant comfort gains. Payback: months. Leave trickle vents and airbricks alone — controlled ventilation is deliberate; draughts are not.

2. Loft insulation — the classic no-brainer. The recommended depth of mineral wool is 270–300mm; many homes have a tired 100mm layer from decades ago. Topping up costs roughly £500–£1,000 installed (much less DIY) and saves in the low hundreds per year in a typical semi. Payback: 2–5 years, then decades of free savings. Insulate and draught-seal the loft hatch too, and don’t squash insulation flat with storage boards — raise them on stilts.

3. Cavity wall insulation. Most homes built after about 1930 have a cavity between brick skins; filling it with blown insulation costs roughly £1,000–£3,000 depending on size and saves £150–£300+ a year. Payback: typically 4–8 years. Get a proper pre-survey — unsuitable walls (exposed to driving rain, faulty damp-proofing) can develop damp problems, and a reputable installer with a CIGA guarantee is worth the extra.

4. Floor, pipes and tank — the small stuff. Insulating a suspended timber ground floor (£100s DIY from below if there’s crawl access), hot-water cylinder jackets (£20, pays back in months), pipe lagging. Individually modest, collectively worthwhile.

5. Solid wall insulation — the expensive one. Pre-1930 solid-walled homes lose the most through walls but cost the most to fix: internal insulation at roughly £8,000–£15,000, external at £10,000–£25,000. Payback: often 15+ years on bills alone, so it usually makes sense when you’re renovating anyway (re-rendering, replastering a room) rather than as a standalone project. Moisture behaviour in old walls matters — use installers experienced with solid-wall homes.

Windows sit awkwardly in the list: going from single to double glazing transforms comfort and noise but at £5,000–£15,000 rarely pays back on energy alone. If existing double glazing is sound, secondary glazing or heavy curtains deliver most of the comfort for a fraction of the cost.

Help with the cost

Support schemes come and go, but currently: ECO4 funds insulation for lower-income households and homes with poor EPC ratings until December 2026 (your energy supplier can check eligibility — ask now, not next spring), and the council-run Warm Homes: Local Grant is its successor in England. Scotland, Wales and Northern Ireland run their own schemes — the grants guide collects them all. Renting? Landlords face rising minimum-efficiency standards and there’s dedicated funding — asking costs nothing. Check gov.uk’s “Improve your home’s energy efficiency” service for what’s live before paying full price.

Two rules for not getting burned

Get three quotes for anything install-priced — this market has a wide cowboy fringe, and prices for identical work vary absurdly. And after any airtightness work, remember ventilation: a sealed home needs its extractor fans, trickle vents and occasional window-opening to avoid condensation and mould. Insulate tight, ventilate right.

The one-line summary

Work down the payback ladder — draught-proofing, loft top-up, cavity walls, then the expensive stuff only alongside renovation — check for grant funding first, and fix the house before buying anything with a compressor or an inverter (then see the heat pump and solar guides).

Last reviewed: August 2026.