What is Part L?

This blog routinely refers to Part L as an important linchpin that supports every word on every blog on this site. So, what is it?

Architects have to design buildings that comply with all volumes of Building Regulations.

Across all nations of the United Kingdom, we have building regulations. These are legal documents that set mandatory guidance for anyone who's involved with building work - not just for new construction sites, but also renovations, extensions and change-of-use works.

Building Regulations are a devolved matter, meaning each country in the UK can create their own. The UK Government is responsible for building regulations in England, but Wales, Scotland, Northern Ireland and the Channel Islands all have their own versions.

In England and Wales, building regulations are written in volumes, called Approved Documents. At the last count, there were 19 volumes starting at Part A (structure and foundations) and finishing at Part T (which is the one with my favourite title: 'Toilet Accommodation').

Some volumes of the Approved Documents are more well-trodden than others, and some are updated more regularly than others, but all are legal requirements which all builders across the country need to adhere to.

The official name for Part L is the 'Conservation of Fuel and Power' - more commonly known as Energy Efficiency. You can download the full document here:

Part L - England (2021)

Part L - Wales (2022)

(I'll cover Scotland in a separate post)

The requirements of Part L vary between residential and non-residential, and new-builds and renovations. This page mostly focuses on the requirements for newly built dwellings.

To comply with Part L, new homes need to show compliance with the SAP calculation. There's a different 'What Is' page to explain that one. For non-residential buildings, the SBEM calculations serves the same purpose.

The design of every building needs to be assessed, and the predicted energy use and carbon emissions are calculated. If the design doesn't meet these targets, improvements will be required to make the design more environmentally friendly.

SAP is used to check three three mandatory targets:

• The Target Emission Rate checks the fuel used in the building isn't responsible for creating high levels of CO².

• The Target Primary Energy Rate checks the energy demand of the heating, hot water, ventilation and lighting systems.

• And the Target Fabric Energy Efficiency (not Wales*) specifically looks at the shell of the building to make sure insulation levels and air tightness are sufficient.

  
  

At completion, air tightness tests are mandatory on all new homes. This test confirms the quality of the build, with a leaky building recording poor results. The results from these tests are fed back into SAP to generate the final 'As Built' reports.

A new addition to the 2021 version of Part L is the requirement to create a photographic evidence portfolio for every new dwelling. These images confirm the continuity of insulation at key points during the construction of the building.

As you may expect given the subject matter, Part L encourages the use of high-efficiency heating systems and low/zero carbon technology. Under the current regulations, a new building will not meet the required targets without some form of green tech - most developers opt for heat pumps or PV panels as standard on all new housing estates.

Limiting heat loss is another key aim of Part L. U-Values are used to measure the predicted losses through the building envelope. Part L sets maximum targets that designs must meet.

Building services are defined as heating, hot water, ventilation and lighting systems. Part L sets out minimum efficiency limits for all building services, and minimum standards for insulation around pipes and ducting.

Part L has evolved over the years to improve the energy performance of our buildings, and as the UK prepares for a net-zero future, Part L definitely has more big updates over the horizon. The next big update is expected in 2026, which will effectively end the use of fossil fuel heating systems in new builds, and set higher expectations for onsite energy generation.

This blog will include news on Part L updates as they're announced.

*In Wales, stricter U-Value standards are used instead of the TFEE target.