Definition: Loft insulation is one of the cheapest effective energy upgrades: insulating an empty loft to the recommended 270mm of mineral wool costs about £750 and saves about £140 (mid-terrace) to £360 (detached) a year, while topping up from 120mm costs about £600 and saves only about £17 to £35 (Energy Saving Trust, July 2026 fuel prices).
The 270mm rule
Many older homes have 100mm or less. Topping up is a half-day DIY-able job, though professional installation ensures even coverage and ventilation gaps at the eaves.
Watch-outs
Don’t compress insulation under boarding — use raised loft legs. Insulate the loft hatch and keep water tanks lagged, as an insulated loft gets colder.
Estimate your numbers: try the free savings calculator or browse all upgrade guides.
See what home insulation cost in your town
Prices for 160 towns, with the grant position for your nation.