Insulation & Energy Calculators

Insulation is one of the most important aspects of UK building design, driven by Approved Document L of the Building Regulations, which sets minimum thermal performance standards for new buildings and extensions. With the UK government's commitment to net zero carbon emissions by 2050, insulation requirements have become increasingly stringent. The 2021 update to Part L introduced significantly lower U-value targets, meaning more insulation is needed in walls, floors, and roofs than ever before.

The U-value measures how effectively a building element (wall, floor, or roof) prevents heat from escaping, expressed in watts per square metre per degree Kelvin (W/m²K). Lower U-values mean better insulation. Current UK Building Regulations require maximum U-values of 0.26 W/m²K for walls, 0.18 W/m²K for roofs, and 0.18 W/m²K for floors in new buildings. Our U-value calculator helps you determine the U-value of your proposed construction, and the insulation thickness calculator works backwards from a target U-value to tell you how thick your insulation needs to be.

Common insulation materials in the UK include mineral wool (Knauf, Isover, Rockwool), rigid foam boards (Celotex, Kingspan, Recticel), and blown insulation for cavities (EPS beads, mineral wool). Mineral wool rolls are the standard choice for loft insulation, with the current recommendation being 270mm total thickness (typically 100mm between joists plus 170mm over the top). Our loft insulation calculator works out how many rolls you need based on your loft area and existing insulation depth.

Cavity wall insulation is one of the most cost-effective energy efficiency improvements for UK homes built between the 1930s and 1990s. Approximately 8 million UK homes have unfilled cavity walls, costing their owners hundreds of pounds per year in wasted heating energy. Cavity wall insulation is installed by specialist companies (registered under the PAS 2030 quality standard) and typically costs £500–£1,500 depending on house size and wall area.

Energy Performance Certificates (EPCs) are mandatory when selling or renting a UK property, rating the home from A (most efficient) to G (least efficient). The average UK home is rated D, and the government has proposed minimum EPC requirements for rental properties. Improving insulation, upgrading the boiler, adding double glazing, and installing renewable energy systems all contribute to a better EPC rating. Our calculators help you understand the thermal performance of your property and plan insulation upgrades that comply with current UK Building Regulations.