Energy & carbon

Part L Building Regulations Explained

Part L of the Building Regulations governs energy efficiency in buildings. This guide explains what it covers, how it applies to new and existing buildings, and why it matters for operations.

Diagram summarising Part L building regulations for facilities and estates teams, covering What Part L covers, Part L for existing buildings and FM and Part L, EPCs, and the bigger picture

In short

Part L of the Building Regulations (England) sets requirements for the conservation of fuel and power — covering insulation, heating and cooling efficiency, lighting, controls, and air-tightness. It applies to new buildings and to certain works on existing buildings, with the aim of reducing energy use and carbon emissions.

What Part L covers

Part L sets minimum energy-efficiency standards for the building fabric and services. For new buildings it governs the overall energy and carbon performance, requiring designs to meet target emission and primary energy rates. For existing buildings, it applies when work is carried out — replacing a boiler, re-roofing, installing new lighting, or extending — requiring those elements to meet current efficiency standards. It also drives requirements for controls, metering, and commissioning so that buildings actually perform as designed.

Fabric efficiency — insulation and air-tightness
Heating, cooling, and ventilation system efficiency
Lighting efficiency and controls
Energy metering and sub-metering provisions
Commissioning and as-built information requirements

Part L for existing buildings and FM

For operational FM teams, Part L matters most when plant is replaced or systems are altered. A like-for-like boiler swap, a lighting upgrade, or an AHU replacement must meet the current Part L standards, which can affect specification, controls, and commissioning. Part L also underpins the metering strategy that lets a building monitor and improve its energy performance. Keeping the as-built and commissioning documentation that demonstrates Part L compliance is part of the building's records.

Part L, EPCs, and the bigger picture

Part L sits within a wider framework of building energy regulation, alongside Energy Performance Certificates (EPCs), minimum energy efficiency standards for lettings, and net-zero commitments. Compliance at construction is only the start: realising the intended performance depends on operation, maintenance, and monitoring over the building's life. Good control settings, working metering, and well-maintained plant are what turn Part L's design intent into actual energy savings.

Related maintenance checklists

Energy Meter Checklist·Electricity Sub-Meter Checklist·Commercial Boiler Checklist·Air Handling Unit (AHU) Checklist·All checklists

How this applies by sector

Commercial & managed property FM

Sources

The regulatory positions on this page come from the following primary sources. Where guidance and legislation differ, the legislation governs — always confirm the requirements that apply to your own site and jurisdiction.

Approved Document L: conservation of fuel and power — GOV.UK
Energy Performance Certificates — GOV.UK

Frequently asked questions

Does Part L apply to existing buildings?

Yes, when work is carried out. Part L applies in full to new buildings, and to existing buildings when you carry out relevant work — such as replacing a heating system, upgrading lighting, re-roofing, or extending. Those elements must meet current Part L standards even though the rest of the building is unchanged.

What is the difference between Part L and an EPC?

Part L is the building regulation that sets energy-efficiency requirements at design and construction or when work is done. An EPC (Energy Performance Certificate) rates the energy performance of a building for sale or letting. Part L governs the standard you must build to; the EPC reflects how the building performs and is required at transaction points.

Who is responsible for Part L compliance?

At construction, compliance is demonstrated through the building control process by the project team. In operation, FM and estates teams maintain compliance when carrying out works on existing buildings, ensuring replacement plant and altered systems meet current standards and that the supporting documentation is retained.

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