Home Insulation: The Complete UK Guide

Bottom line

For nearly every UK home, insulation is the highest-ROI energy upgrade you can make.

Two jobs are worth doing on payback alone. Insulating a bare loft costs about £750 on a semi and saves about £190 a year, so roughly four years. Cavity wall is around £2,200 on a semi and saves about £200 a year on EST's own published figures, so about eleven years. Worth knowing that EST's prose claims five years or less while its own cost and savings tables give eleven, and we've gone with the tables. Topping up a loft that already has 120mm is a different story: £600 to save £17 a year, so do that one for comfort and heat pump readiness. ECO4 may cover work in full if you qualify and it closes on 31 December 2026, so check the grants before you pay anything. The hard case is solid-wall homes: the Trust puts internal at around £12,000 and external at around £15,000 for a semi, against roughly £280 a year saved, so on payback alone it never really stacks up without a grant. Do it for comfort and for a house that holds heat, not for the maths. Exposed coastal walls and listed buildings need extra care too.