Part L Building Regulations: Preparing for 2025 Updates

A New Era for Energy Efficiency in the Built Environment

The UK government is preparing to implement major changes to Part L Building Regulations in 2025, aligning with the Future Homes Standard (FHS). These updates aim to deliver “net zero ready” buildings—designed for low-carbon heating and high energy efficiency. Applicable to both residential and non-residential properties, the upcoming changes represent a pivotal shift in construction and sustainability performance expectations.

What Is Part L of the Building Regulations?

Part L Building Regulations define the minimum energy performance requirements for buildings in England. Focused on the conservation of fuel and power, they set benchmarks for insulation, heating systems, lighting, and ventilation to reduce overall energy use and carbon emissions. The 2025 update reinforces the UK’s legal commitment to net zero by 2050 and is part of a broader move to decarbonise the built environment.

Key Proposed Changes to Part L

1. Transition to Low-Carbon Heating Systems

The 2025 standards will require new homes to adopt low-carbon heating systems, effectively phasing out gas boilers in favour of options such as:

• Air source and ground source heat pumps
• District heat networks
• Solar thermal systems (where applicable)

This transition will play a central role in reducing emissions by 75–80% in new homes compared to those built under previous regulations.

2. Improved Energy Efficiency Standards

The updated Part L Building Regulations will strengthen requirements for building fabric performance and efficient services, including:

• Enhanced wall, floor, and roof insulation
• High-performance glazing to reduce heat loss
• Mechanical ventilation with heat recovery (MVHR) for better indoor air quality and energy efficiency
• Encouragement (but not requirement) to integrate solar PV and energy storage solutions where feasible

3. Stricter Airtightness Requirements

Airtightness will remain a critical part of compliance. All new homes must undergo air permeability testing with a maximum target of 8 m³/(h·m²) at 50 Pa. Tighter construction detailing and quality assurance will be required to reduce heat loss and meet the defined standards.

4. New Compliance Metrics and Testing

Compliance with Part L 2025 will be assessed using updated metrics including:

• Primary energy targets
• Carbon emission rates (aligned with Future Homes Standard benchmarks)
• Post-construction verification via airtightness tests and SAP or Home Energy Model (HEM) assessments

How to Ensure Compliance with Part L 2025

1. Stay Updated on Regulatory Guidance

Industry professionals should follow updates from:

• Department for Levelling Up, Housing and Communities (DLUHC)
• UK Green Building Council (UKGBC)
• Building Research Establishment (BRE)

These sources provide essential updates on the Future Homes Standard and Part L Building Regulations.

2. Collaborate with Energy and Compliance Consultants

Work with accredited assessors and energy consultants to deliver accurate SAP (for domestic buildings) or SBEM (for non-domestic buildings) calculations. As HEM is introduced, ensuring correct modelling and design-stage guidance will be key.

3. Upskill Your Teams

Training in energy-efficient construction, airtightness detailing, and installation of low-carbon systems will help ensure readiness ahead of the 2025 deadline.

4. Adopt Low-Carbon Technologies Early

By incorporating heat pumps, MVHR, and enhanced fabric measures into current projects, developers can de-risk future compliance and meet rising market expectations.

5. Strengthen Testing and Quality Assurance

To ensure buildings meet Part L 2025 criteria, teams should conduct:

• Air tightness testing on all plots
• Thermal imaging (as a diagnostic or quality tool)
• Updated SAP or HEM calculations post-build

In addition, thermostatic radiator valves (TRVs) will be mandatory on all radiators except where a room thermostat is already in place.

What These Changes Mean for the Construction Industry

The 2025 uplift to Part L Building Regulations will drive a step change in design, specification, and compliance behaviour across the sector. While the initial impact may involve more rigorous planning and investment, the long-term benefits are clear:

• Lower energy bills for occupants
• Increased long-term value and performance of new builds
• Alignment with ESG goals and future planning policy

The updated Part L Building Regulations signal a decisive move towards decarbonisation and more sustainable development. For developers, architects, and contract

Not sure where you stand?  Get in touch with enevo to see how we can help you meet Part L Building Regulations