CPD 07 2022: Part L Compliance Considerations – Building | Building Design


This Knauf Insulation sponsored CPD spells out the key elements of the new additions to the Building Regulations that are aimed at improving energy efficiency in homes, and explains which materials can help deliver the best results for an energy efficient project. Deadline: 26th August 2022

ADL will introduce a new level of scrutiny on housebuilding

What does Approved Document L cover?

Updates to Approved Document L (ADL), or Part L, of the Building Regulations for England, came into force on 15 June 2022. The regulations address the conservation of fuel and power and apply to all building projects in England.  

To accommodate the adjustments housebuilders need to make, the government has established a transition period for compliance. 

The updates do not apply where a building notice, initial notice or full plans have been provided to a local authority before 15 June 2022, provided that building work on any such scheme is started before 15 June 2023.

What are the headline changes?

The updated regulations aim to lower the operational carbon emissions of new homes, raise fabric efficiency standards and introduce a new level of quality control.  

The updates require all new homes to produce 31% fewer operational carbon emissions compared with the Part L 2013 regulations. This increase in energy efficiency can be achieved through any combination of fabric, heating systems and renewable technologies.

The government has stressed the 31% reduction will act as a stepping stone towards a 75% reduction by 2025, as set by the Future Homes Standard.

New ‘primary energy’ metric 

Part L defines “primary energy” as energy from renewable and non-renewable sources that has not undergone any conversion or transformation process. The revised Part L of the Building Regulations raises energy efficiency standards by  introducing tighter limiting U-values for new fabric elements and air permeability in new-builds.

Limiting U-values for new fabric elements in new dwellings

Housebuilders also need to ensure that new homes meet targets for: 

  • Primary energy – a new metric, influenced by fabric and fuel 
  • Emissions – influenced by fabric and fuel 
  • Fabric energy efficiency – influenced by fabric only. 
Part L 2021 W/(m2K) Part L 2013 W/(m2K)
Roof 0.16 0.20
Wall 0.26 0.30
Floor 0.18 0.25
Party Wall 0.20 0.20

Sourced: Building regulations approved document l 2021
 and 2013

To allow for design flexibility, housebuilders can meet the emission and primary energy target rates through a combination of fabric and fuel. However, insulation must be used in order for a home to meet its target fabric energy efficiency rate.

All three target rates must be calculated using the latest version of the government’s Standard Assessment Procedure (SAP), through the latest SAP software. 

New Buildings Regulations England Part L report

Under the new regulations, housebuilders need to demonstrate continuity of insulation, using a new Buildings Regulations England Part L (BREL) report. 

Two BREL reports must be submitted for a new-build:  

  • Design stage BREL – showing that the house specification has the potential to meet its target rates 
  • As-built BREL – showing that the target rates have been met.

Photographic evidence

The as-built BREL report will require housebuilders to supply a photographic record of key stages during construction, to show thermal continuity and quality of insulation.

The photos should show typical details of the build: for example, insulation at external door thresholds and ground floor-to-wall junctions. In some instances, close-ups may be required to show smaller details and all images should be geo-location, date and time stamped. Anyone can take the necessary photographs; however, they must be in a digital format and of a high enough resolution to be used for auditing purposes. 

The new level of scrutiny introduced by the revised Part L indicates a clear regulatory shift towards measuring a home based on its as-built performance rather than its notional design. While the immediate focus is on energy efficiency, housebuilders will soon need to consider the bigger picture of real performance, including factors such as fire safety and embodied carbon.  

The bigger picture

The 2018 Independent Review of Building Regulations for Fire Safety – known as the Hackitt review – recommended an outcomes-based approach to regulations, with guidance that focusses less on meeting arbitrary targets and more on informed assessment and demonstration of safety. This again indicates a move away from notional tick-box exercises, towards adopting an emphasis on real-world performance.

The government’s new Building Safety Act is also introducing new requirements to ensure more products are safe, with a view to establishing a National Regulator for Construction Products to oversee and enforce the rules. A New Homes Ombudsman Scheme will also empower homeowners to dispute sub-standard work. 

Some local authorities have chosen to get ahead of the curve by taking action within their own jurisdictions. For example, building regulations for England and Wales currently ban the use of combustible materials on the external walls of certain buildings over 18m. As of December 2022, legislation in England will also ban nearly all combustible materials on facades of residential buildings over 11m (some combustible materials will still be permitted on buildings between 11m and 18m as part of a system that has passed a large-scale test). However, the mayor of London has already imposed rules restricting the use of combustible materials on external wall systems on all future developments on Greater London Authority owned land, irrespective of height or use.

DriTherm® Cavity Slab insulation: Glass mineral wool has the lowest embodied carbon of any mainstream insulation material

Carbon reduction strategies

This “go further, faster” approach is being applied to tackle carbon reductions too. While the Future Homes Standard has established targets for 2025, the RIBA’s 2030 Climate Challenge recommends adopting a 2025 target of 800 KgCO2e/m2 as a minimum for new-builds now at the design stage. 

The homebuyer market also shares this attitude, according to recent research from the Home Builders Federation showing that a good energy performance certificate is now one of the top three factors taken into account by potential housebuyers seeking to purchase a property. 

Studies also indicate that over three-quarters of homebuyers are likely to consider purchasing a green home and that housing associations are equally carbon conscious, with many planning to make their homes net zero by 2050, according to a National Housing Federation survey. 

With customer expectations growing, tighter regulations on the horizon and an increasing focus on real world performance, the pressure on housebuilders to close the performance gap has never been greater.

How can insulation help?

While a product might tick the box on paper, in practice there are multiple ways it can fall short of its performance potential. 

For example, building designs often rely on a perfect installation to achieve optimal thermal performance. Unfortunately, conventional rigid board insulation by its nature does not flex. So if a substrate is not perfectly uniform, it will not sit flush against it, leading to thermal gaps and heat loss. 

Even the most scrupulous installer faces the challenge of subsequent construction work disturbing their insulation and compromising its performance. 

By contrast, mineral wool’s flexible structure adapts to minor imperfections in a building’s substrate, maintaining close contact. Where individual rolls or slabs meet, the strands also knit together, eliminating air gaps. This inherent buildability makes mineral wool easier to install correctly, maximising its real-world thermal performance.

Similarly, passive fire safety measures, such as insulation, function as part of larger systems within a building’s cavities, often involving third-party elements like fire breaks. As with thermal performance, deviation from the design specification can prevent these systems from performing correctly. If this happens, the use of combustible materials creates a further level of risk, which is entirely unnecessary.

Get it right from the start

he simplest approach for housebuilders is to specify non-combustible materials, such as mineral wool, from the outset. 

Products such as mineral wool can achieve thermal performance without compromising on safety. Not only does this allow for peace of mind, it could also help housebuilders to avoid any financial penalties that could be incurred as a result of future changes to the regulations as they develop over the coming years.

When it comes to achieving long-term sustainability goals, such as net zero homes, lowering a building’s operational carbon will not be enough. In order to make significant change, housebuilders will also need to consider a building’s embodied carbon, which is the total greenhouse gas emissions released in producing the building. This includes emissions caused by the extraction, manufacture, processing, transportation and assembly of every product and element used in the build (as described in the UK Green Building Council’s March 2017 publication Embodied Carbon: Developing a Client Brief).

In fact, it is worth keeping in mind that as operational carbon is driven down in the coming years, a building’s embodied carbon will make up a larger proportion of its overall emissions – a change that could become significant as regulations continue to evolve.

Glass mineral wool has the lowest embodied carbon of any mainstream insulation material, while still delivering reliable, high-quality thermal and fire safety performance. Specifying glass mineral wool allows housebuilders to lower the overall carbon footprint of their homes, without compromising on the other qualities their customers value.

 What are the best ways to comply?

There is no single right way to comply with Part L. Different builds require different approaches and under the new regulations housebuilders will still have the right to choose their own optimal solution.  

 Part L contains an example notional dwelling, but this is purely illustrative and attempting to replicate it will rarely be the most effective route to compliance. Instead, housebuilders should decide on the ideal balance of fabric and technology in order to meet Part L requirements and suit their own priorities.

Below are some example scenarios, along with Part L-compliant “recipes” using non-combustible, low-embodied carbon insulation materials. (These example recipes have been produced prior to the release of the latest SAP software and are intended for illustrative purposes only.)

The three different scenarios are all based on a five-bedroom detached house featuring three wet rooms, 192m2, and five occupants, but differ in being designed to prioritise either simplicity, technology or longevity. 

Key takeaways 

  • Updates to Part L (Approved Document L) came into force in England on 15 June 2022.
  • Housebuilders are required to lower operational carbon emissions of new homes, raise fabric efficiency standards and increase quality control.
  • The updates indicate a future shift towards measuring the real performance of homes.
  • Regulations and homebuyer demands are evolving across the board, including higher expectations for fire safety and low carbon performance, as well as energy efficiency.
  • Housebuilders, architects and designers must work to close the performance gap and specifying the right insulation will be key to their success.
  • Each business must find its best route to Part L compliance, based on individual priorities.

Example 1: Prioritising simplicity

For simplicity, a volume housebuilder might choose to change very little about their fabric and heating specifications, and install rooftop photovoltaic panels, to increase energy efficiency. This approach is particularly relevant for developments which occur within the transition period to the new Part L, as it offers a route to compliance without the need for costly redesign work. See the table below.

Example 2: Prioritising technology

For larger sites, which begin after the transition period ends in June 2023, some housebuilders might opt to continue with their usual fabric specification but introduce air-source heat pumps. Planning further ahead allows more time for design work to account for alternative technology, for supply chains to adapt and for products to become available in the required quantities. The table showing the specification choices for this example is shown below.

Example 3: Prioritising longevity

By contrast, a more bespoke build might call for higher-efficiency insulation, allowing flexibility to consider different types of heat source. This approach prioritises the reliability and longevity of fabric, while allowing the housebuilder to choose technology based on project-specific factors such as budget, preference or available space. The table for this example is also to be found below.

Example 1: Prioritising simplicity

Example 2: Prioritising technology

Example 3: Prioritising longevity



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