What is Part L of the Building Regulations and what does it mean for solar?

What is Part L of the Building Regulations?

Part L of the Building Regulations sets out the requirements for the conservation of fuel and power in new and existing buildings in England. It is the primary legislative instrument through which the government enforces energy efficiency standards in construction.

Part L applies to all new buildings, extensions, and material changes of use. For housebuilders and developers, it governs how energy-efficient new homes must be, covering insulation, heating systems, windows, and low-carbon energy generation including solar PV.

What changed in the 2021 Part L uplift?

The most significant recent update to Part L came into force in June 2022, based on regulations published in December 2021. The 2021 uplift tightened the carbon emission limits for new homes by approximately 31% compared to the previous standard set in 2013.

This was an interim step. The government described it as a stepping stone toward the Future Homes Standard, with the intention of raising requirements significantly further by 2025.

Why has solar PV become a standard Part L compliance route?

Meeting the 31% improvement target set by the 2021 uplift is challenging through fabric improvements alone, particularly on smaller plots where adding wall insulation has practical limits. Solar PV generation reduces a home's net carbon emissions directly, making it one of the most cost-effective ways for housebuilders to close the compliance gap.

As a result, solar PV has moved from an optional extra on new builds to a near-standard feature on many developments, particularly those with south-facing or west-facing roof pitches. Developers who designed solar into the fabric specification from the start generally achieve compliance more easily and at lower cost than those who retrofit it.

What is the Future Homes Standard?

The Future Homes Standard is a proposed revision to Part L that will require new homes to produce 75 to 80% fewer carbon emissions than homes built to the pre-2021 standard. The government's stated intention is to implement this by 2025, though implementation timelines for building regulations changes have historically shifted.

Under the Future Homes Standard, heat pumps and solar PV are expected to become near-universal on new homes, since meeting the target through fabric improvements alone would be extremely difficult and expensive. Developers planning schemes with a build programme extending to 2025 and beyond should be designing with this in mind.

Does MCS certification matter for Part L compliance?

Yes. For solar PV to count toward a building's Standard Assessment Procedure (SAP) rating, which is the methodology used to demonstrate Part L compliance, the installation must meet the relevant quality standards. MCS certification provides this assurance.

Planning conditions on many sites also specifically require MCS-certified installation. If a development's planning permission includes conditions about renewable energy, confirming the certification requirements before appointing an installer is advisable.