Energy and carbon in buildings: understanding Part L and the Future Homes Standard

What Part L covers

Approved Document L gives guidance on meeting the energy requirements of the Building Regulations. It has volumes for dwellings (L1) and for buildings other than dwellings (L2), with separate guidance for new buildings and for work on existing buildings. It deals with:

• Energy performance and carbon emissions of new buildings, set against a notional building.
• Fabric performance: insulation levels, windows and doors, and limits on heat loss through the building envelope.
• Airtightness and testing. See Airtightness and ventilation.
• Building services: heating, cooling, ventilation, hot water and lighting, and their efficiency and controls.
• Thermal bridging. See Thermal bridging.
• Commissioning and providing information to the owner.
• Overheating in some contexts, alongside Part O. See Overheating.

How compliance is shown

Designers use approved calculation methods, such as SAP for dwellings and SBEM or dynamic modelling for other buildings, to predict the energy and carbon performance and check it against the limits. After completion, an Energy Performance Certificate is produced. The results must also be supported by the airtightness test and commissioning.

Approved Document L gives guidance on meeting the energy requirements of the Building Regulations.

The direction of travel

Over the years, standards for new buildings have become stricter, with a focus on reducing carbon and moving away from fossil-fuel heating. Government has said that further changes to the regulations will follow, under the heading of a Future Homes Standard and a Future Buildings Standard, intended to produce homes and buildings that are "zero-carbon ready", for example by using low-carbon heating, such as heat pumps, and well-insulated, well-sealed construction. The exact requirements and dates should be checked at the time.

Designing well, not just to the minimum

The best results come from design decisions made early:

1. Form and orientation: compact forms, good use of sun and shade.
2. Fabric first: good insulation, continuous and airtight, with few thermal bridges.
3. Efficient systems: low-carbon heating, such as heat pumps, with efficient ventilation, lighting and controls.
4. Renewables: solar panels and other sources where suitable. See Solar panels on buildings.
5. Avoiding overheating.
6. Good commissioning and handover, so that the building performs as designed.

The performance gap

Many buildings use more energy than predicted. Causes include poor workmanship, systems that are not properly commissioned, and occupants who do not know how to use them. Post-occupancy checks can find out. See Post-occupancy evaluation.

Carbon beyond operation

Part L focuses on the carbon from running a building. The carbon in making and building it, called embodied carbon, is also important, though regulation has treated it differently. See Embodied carbon in plain language.

In short

Reduce demand with fabric, use efficient low-carbon systems, test and commission, and check the rules in force for your project.

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