UK Standard

Building Regs — Part L — Conservation of Fuel & Power

The Building Regulations — Approved Document L (Conservation of fuel and power)

In short: Approved Document L sets UK building energy efficiency limits, including fabric U-value targets and 270mm loft insulation standards.

What Building Regs — Part L covers

Part L drives the insulation depths and U-values that the loft, floor and wall insulation calculators work to (for example the recommended ~270mm of loft insulation).

It works alongside heat-loss sizing: a better-insulated fabric under Part L reduces the radiator output required under the CIBSE method.

Apply this standard

Calculators that use Building Regs — Part L

Loft Insulation Calculator
Rolls needed to reach the recommended 270mm depth to current Building Regs.
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Floor Insulation Calculator
PIR boards or mineral wool for suspended or solid ground floors.
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Wall Insulation Calculator
Insulated plasterboard or stud-and-slab quantities for internal wall lining.
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Radiator BTU Calculator
Room heat loss using the CIBSE method with radiator sizing and ASHP correction factor.
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Official source: GOV.UK — Approved Document L. Figures on this page are a plain-English summary for estimating purposes — always refer to the published standard for compliance.