Part L Building Regulations 2021 – What You Need to Know


In 2021, the UK government updated the Approved Document L to state enhanced standards for energy efficiency. These adjustments took effect on 15th June 2022 and covered the conservation of fuel and power for buildings and other dwellings. 

Building regulations provide designers with general guidance on the expected performance of construction work and the materials used. These regulations also offer some solutions to address common building situations and to meet the latest standards. 

These new regulations are important to architects, builders, HVAC technicians, plumbers, and electricians. However, if a project’s building notice, full plan, or initial notice was submitted before the 15th of June 2022, the old regulations still apply. 

Continue reading to discover more about Part L Building Regulations 2021 and the fundamental changes introduced in the update. 


What is Part L Building Regulations of 2021?

Part L 2021 Building Regulations focus mainly on the conservation of fuel and power in new-build and existing buildings, plus non-domestic buildings. 

The regulations introduced significant upgrades to insulation requirements, the use of heating systems, and improved ventilation. Additionally, the government upgraded the current energy efficiency standards and introduced new metrics to calculate carbon emissions and energy consumption.

Homes and structures built following these new building regulations outlined in detail are expected to be more environmentally friendly, cost-effective, and comfortable. These regulations are set to serve as a “stepping stone” in anticipation of the scheduled publishing of The Future Homes Standard and Future Buildings Standard in 2025.

Key Changes to Building Regulations

There are 2 volumes revised with the new Part L Building Regulation requirements, each covering various aspects of construction. Here is a summary of what they entail:

  • Volume 1 – Existing and New Dwellings: This volume focuses on the improvement of existing buildings and new-build constructions. There are some new or tightened requirements surrounding the standards around these dwellings. 
  • Volume 2 – Buildings Other Than Dwellings: This updated volume provides guidelines on the required energy standards for commercial buildings or other existing buildings that aren’t used as residential dwellings. 

Target Primary Energy Rates (Applies to Both Volumes) 

Previously, building designers needed to focus on meeting the minimum requirements for The Target Carbon Emission Rate (TER) and Target Fabric Energy Efficiency (TFEE). However, with the implementation of the Part L update in 2021, designers also need to consider the Target Primary Energy Rate (TPER) metric. This discloses the maximum yearly energy use allowed for new buildings, existing structures, and non-domestic projects. 

CO2 Emission Reduction Targets (Applies to Both Volumes) 

A very significant uplift was introduced with regard to the carbon emissions in new homes. It’s stated that new homes should be designed and constructed in such a way that they produce 30% less carbon emissions than the current standards. Meanwhile, in non-domestic buildings, the aim is to reduce CO2 emissions by 27%. 

These metrics are essential in order to assist the UK construction industry in meeting the 2025 Future Homes Standard (FHS). This aims to drastically reduce carbon emissions, prioritise low-carbon heating systems, and minimising heat loss in every building being built. 

Building Fabrics: Enhanced U-values (Applies to Both Volumes)

New fabric efficiency standards focus on full fabric specifications, insulating elements, and tightening U-values or thermal performance. U-values for construction elements such as walls, doors, and windows have changed with the introduction of the latest Part L construction requirements. 

With new standards for minimal thermal efficiency, designers and architects alike need to focus a lot more on meeting the updated compliance standards for energy performance. 

Air Testing Requirements (Applies to Both Volumes) 

As with improving building elements, enhancements to air permeability and air testing requirements of new and existing homes and non-domestic buildings have been introduced. 

As per old requirements, non-dwelling buildings could avoid air testing if they presented measurements higher than 500m2 and projected an assumed air permeability measurement of 15 m3/(h.m2) at 50Pa. With new regulations, buildings with less than 500m2 and the same air permeability figures can also avoid air testing. 

For a domestic project, natural ventilation can be implemented if a building has an air permeability rate higher than 3m3/(h.m2) at 50Pa. For data better than this, continuous mechanical extract systems can be implemented. 

Standard HVAC Services Efficiencies (Applies to Both Volumes) 

These guidelines specify the minimum standards for heating, ventilation and air conditioning services. 

Natural gas boilers with outputs below 2MW need to boost efficiency by 93%. Whereas with numbers above 2MW, they need to be 88% more efficient This document also outlines requirements for water heating systems, cooling units and self-regulating devices, and minimum lighting efficiency metrics. 

However, Volume 1 does suggest that electrical heating systems can help reduce carbon emissions better than gas boilers. So opting for electrical heating might present a better chance of passing SAP and Part L requirements.

Site Photographs (Applies to Volume 1)

As per the Part L 2021 new requirement guidelines, photos must be taken at different construction phases, as they near completion, and provided to the building control body and the energy assessor. The photographs serve as an accurate record of the site and construction process. 

Thermal Bridging (Applies to Volume 1)

The use of accredited construction details (ACDs) is being removed when calculating thermal bridging. ACDs are a set of standardised junction details and their relevant PSI values that developers use to reach minimum performance standards. 

However, using default PSI values doesn’t provide a comprehensive insight into the projected performance of a building, making the construction prone to a performance gap. With tightened regulations, it’s more important than ever to have accurate PSI value calculations as a requirement. Using default values can risk a shortfall in energy performance and compliance standards. 

PSI value calculation tools like AutoPSI can help calculate  PSI values with speed and precision. 


AutoPSI: Stay Compliant with Precise PSI Value Calculations  

With the introduction of Part L Building Regulations 2021, it is important to take a detailed look at the updated metrics mentioned and employ efficient tools to meet the current building regulations. 

AutoPSI offers an innovative, online-only software that simplifies the calculation of accurate PSI values. With the option to customise junction details, construction designers are able to test and optimise building designs to ensure the most optimal thermal performance and building compliance

Pass SAP assessments with ease using AutoPSI. Sign up for a free seven-day demo today to find out how our software can help you meet part L Building Regulations 2021.