Loft Insulation Savings Calculator

About this calculator

A material's U-value measures how much heat passes through it — expressed in watts per square meter per degree Kelvin (W/m²K) — so a lower U-value means better insulation. Upgrading loft insulation lowers the roof's U-value, and the annual heating energy saved is calculated as the loft area multiplied by the difference between the old and new U-values, multiplied by the average temperature difference between inside and outside over the heating season, converted into energy cost using the local energy price.

Homeowners run this calculation before spending money on loft insulation upgrades because the return on investment varies enormously depending on the starting U-value — going from poor, aging insulation (a high U-value) to modern standards saves dramatically more energy per pound spent than topping up insulation that already meets current building-code minimums, where the diminishing returns mean payback periods stretch out much longer.

This calculator takes your loft area, current and new U-values, and local energy price, and returns your estimated annual heating cost savings from the insulation upgrade.