Part L of the Building Regulations deals with the conservation of fuel and energy, setting minimum energy performance and insulation standards for new buildings, extensions and, in certain cases, renovations. Requirements differ between dwellings and non-dwellings, and standards have been progressively tightened, including for new homes to support nZEB (nearly zero energy building) performance.
Part L of the Second Schedule to the Building Regulations covers the conservation of fuel and energy, and sets minimum requirements for the energy performance of buildings, including levels of thermal insulation, air-tightness, efficiency of heating and hot water systems, and, more recently, the contribution of renewable energy technologies. Separate Technical Guidance Documents exist for dwellings and for buildings other than dwellings, reflecting their different typical construction and use patterns.
For new dwellings, Part L requirements have been progressively strengthened over successive revisions, most notably to support the nearly zero energy building (nZEB) standard, which requires very high levels of energy performance and a significant proportion of energy demand met from renewable sources. Extensions and material alterations to existing dwellings are also subject to Part L requirements, though the specific standard applied and the extent of works required can depend on the nature and scale of the project, and reasonable provision is generally expected rather than requiring a full nZEB upgrade of the entire existing dwelling in every case.
Compliance with Part L for new dwellings is normally demonstrated through a Building Energy Rating (BER) assessment carried out by a registered BER assessor, alongside the design and construction details submitted as part of the building control process. Because the technical calculation methods and specific thresholds are detailed and can change, current requirements should be checked against the latest Technical Guidance Document L and confirmed with a competent designer.