4th January 2022

Part L Changes Confirmed

Technical Manager Ali Riza considers the implications of the now confirmed changes to Part L.

The much-delayed publication of the new Part L Regulations on Thermal Efficiency for new buildings confirms the scale of change and accelerates the progress towards zero carbon housing.

Published in mid-December by the Department of Levelling up, Communities and Housing, the latest revision to Conservation of Fuel and Power, Approved Document L of the Building Regulations is a “stepping stone” on the pathway to zero carbon homes. It sets the ambitious target of an interim 31% reduction in CO2 emissions over 2013 standards for dwellings.

H+H will be publishing a detailed summary, focusing on the implications for the design of external walls in January, but the headline changes are quick to see.

  1.  The requirement to consider the thermal performance of the building fabric is retained, ensuring that the majority of the thermal performance of new homes is dictated by the way they are built. This entirely makes sense as that performance will remain constant throughout the life of the building and is not dependant on occupant behaviour or the consistent performance of any technology. In practical terms, the U-Value requirement for external walls will now be 0.18 W/m2K.
  2. The regulations also acknowledge that there is a limit to what can be achieved by fabric performance alone and it will be difficult to achieve the required CO2 emissions performance without the inclusion of low or zero carbon heating systems or photovoltaic panels.
  3. There is a new focus on thermal bridging. The regulations now require the submission of detailed design drawings for junctions together with on-site inspections and photographic evidence. Technically this is a huge issue, as poor detailing or incorrect construction of junctions can completely compromise the thermal performance of the building in use.  H+H has produced its own set of calculations and design guides, giving a range of solutions for various wall constructions. 
  4. Air pressure tests will need to be carried out on every new home on site to ensure air tightness performance is achieved.
  5. The time delay before the new performance standards will apply to completed homes is dramatically reduced. Transitional arrangements will apply to individual buildings rather than whole sites and all new homes that submit plans after June 2022 or have not begun construction before June 2023 must comply.
  6. For simplification, requirements for new building and work on existing buildings have been combined into one document and are more consistent for both.


Overall the changes are very much in line with expectations, but that should not distract attention from the fact that they represent a really significant shift towards zero energy homes.

H+H is well-prepared for the changes and has already compiled detailed technical guidance on how to meet the new thermal performance requirements with standard wall constructions. 

The inherent thermal efficiency of aircrete as a material for the inner leaf of external walls will make the material an even more attractive choice for housebuilders.