Loft insulation is the single most cost-effective energy efficiency upgrade in most UK homes — but only if installed at the right depth. Here's the maths, the savings, and the current government grants.
Up to 25% of a home's heat escapes through an uninsulated roof. Loft insulation is typically the cheapest and most impactful energy upgrade available — payback periods of under 2 years are common. Here's everything you need to calculate your specific case.
The current Building Regulations recommendation for loft insulation is 270mm (about 10.5 inches). Most UK homes built before the 1990s have either no insulation or the old standard of 100mm — both cases leave significant heat loss on the table.
Note the diminishing returns above 100mm — the biggest gains come from the first 100mm. Going from 100mm to 270mm adds significant value but less dramatically than the first layer.
Mineral wool rolls (glasswool or rockwool) are the standard product. They're typically sold in rolls covering 5–8 m² at a standard 100mm depth.
These figures from the Energy Saving Trust assume average gas heating and typical UK weather. Payback on DIY installation (materials ~£300–500) is typically 1–2 years. Professional installation of an empty loft typically costs £300–600.
UK homeowners may qualify for free or heavily subsidised loft insulation through the government's Great British Insulation Scheme (GBIS). Eligibility is based on EPC rating and household income. Homes with EPC D–G and household income under £36,000 qualify for full free installation. Check the gov.uk website for current eligibility — grants change frequently.