How to Comply with Part L Building Regulations for New Build Dwellings in the UK

When designing or constructing a new build dwelling in the UK, one of the most critical regulations to consider is Part L of the Building Regulations. Part L sets standards for the conservation of fuel and power, ensuring that homes are energy-efficient, low-carbon, and comfortable to live in. With the latest Part L 2021 updates and the move towards the Future Homes Standard, it’s essential to understand how to meet these requirements efficiently.

In this guide, we’ll explain the best strategies to comply with Part L, including tips on SAP calculations, airtightness, heating systems, and fabric-first design.

1. Understanding Part L of the Building Regulations

Part L requires new homes to meet specific energy efficiency targets, focusing on:

• Fabric efficiency (walls, roofs, floors, windows, doors)

• Primary energy use

• CO₂ emissions

• Airtightness standards

Compliance is measured using SAP (Standard Assessment Procedure) calculations, which evaluate the building’s overall energy performance. This is why early planning and collaboration with a SAP assessor is crucial.

2. Adopt a Fabric-First Approach

A fabric-first approach is the most reliable way to meet Part L standards. Key steps include:

• Installing high-performance insulation in walls, roofs, and floors

• Using triple-glazed or low-U-value double-glazed windows

• Reducing thermal bridging at junctions and detailing

• Ensuring airtight construction with membranes, tapes, and sealing

Focusing on the building fabric reduces energy loss, keeps running costs low, and is more cost-effective long-term than relying solely on renewable technology.

3. Airtightness and Ventilation

Part L sets minimum air permeability standards (typically 8 m³/(h·m²) at 50 Pa). Achieving this requires:

• Careful detailing during construction

• Blower door testing to verify airtightness

• Integrating mechanical ventilation with heat recovery (MVHR) or efficient extract systems to maintain indoor air quality

Balancing airtightness and ventilation is essential for energy efficiency and occupant comfort.

4. Low-Carbon Heating Systems

Part L encourages low-carbon heating solutions, including:

• Air source heat pumps (ASHPs)

• Underfloor heating with low-temperature systems

• Efficient hot water systems, with well-insulated cylinders

• Optional solar PV panels to offset primary energy consumption

Selecting the right combination early in the design phase ensures compliance and reduces future retrofit costs.

5. Work with SAP Assessors Early

Many developers leave SAP assessments too late. To avoid redesigns:

• Engage a SAP assessor during the design stage

• Use draft EPCs (Energy Performance Certificates) to verify compliance

• Adjust insulation, glazing, and heating systems before construction

Early engagement with a SAP assessor ensures your dwelling meets Part L efficiently and avoids costly last-minute changes.

6. Future Homes Standard Compliance

Part L 2021 is a step towards the Future Homes Standard (2025), which will require a 75–80% reduction in carbon emissions compared to 2013 regulations. By aiming above minimum standards now, developers can:

• Future-proof new build dwellings

• Reduce running costs for homeowners

• Avoid expensive upgrades to meet future regulations

7. Practical Compliance Tips

• Coordinate across trades to ensure airtightness and insulation are installed correctly

• Specify certified products like BFRC-rated windows and insulation with declared lambda values

• Document construction for Building Control, including airtightness tests and commissioning certificates

• Educate homeowners on operating low-carbon systems efficiently

Conclusion

Complying with Part L of the Building Regulations for new build dwellings isn’t just a legal requirement—it’s an investment in long-term comfort, energy efficiency, and sustainability. By prioritising a fabric-first approach, planning airtightness and ventilation together, selecting efficient heating systems, and involving a SAP assessor early, you can achieve compliance confidently.

Start early, design smart, and aim higher than the minimum standard to create homes that are ready for the low-carbon future.

Disclaimer: This article is for general informational purposes only and does not constitute legal or professional advice. Always consult relevant professionals and local authorities before undertaking any development or change of use.