Definition: Loft insulation is the cheapest effective energy upgrade: topping up to the recommended 270mm of mineral wool costs £300-£600 and saves £150-£250 a year.

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.