New Part L 2021 - England

Changes have been made to Building Regulation Part L (England) 

Part L 2021: Conservation of Fuel and Power took effect on 15th June 2022 for use in England. It does not apply to work subject to a Building Notice, full plans application or initial notice submitted before this date, provided the work was started on site before 15th June 2023. 

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Outline of the main changes that have been made 

Part L (England) 2021 sees a reduction in the number of Approved Document volumes from 4 to 2.
Volume 1: Dwellings 

Volume 2: Buildings other than dwellings 

Work to existing buildings is now incorporated into each of the above, rather than being covered by separate volumes as it is currently. 

New U-values required for  flat roofs and roofs with integral insulation are shown in the tables below. 



  • Top-lit buildings are those that primarily use roof glazing  as a source of daylight (e.g. warehouses, sports halls), side-lit buildings use primarily  windows. 
  • Extensions in Buildings other than Dwellings > 100m² and  > 25% area of existing building are treated as a New Building. 
  • Replacement roofs are construed to be those where the structure is replaced (e.g. through fire damage) but some Building Control Officers may interpret a re-deck as falling under this category. For this reason it may be prudent to treat projects where a re-deck is required as a Replacement roof when on a Dwelling, thus aiming for a U-value of 0.15W/m²K rather than 0.16W/m²K. 
  • Renovation of a flat roof is defined in the Approved Documents as “Replacing the waterproofing membrane”.  It has been recognised in the past that if the existing waterproofing is overlaid then the work is classed as a “repair” and does not fall under the requirements of the Building Regulations to be thermally upgraded. However it would be good practice to do so. 
  • Renovating a roof to the U-values stated in the above tables applies to the whole roof  when more than 50% of the individual roof surface is renovated, or when more than 25% of the external building envelope is renovated. 
  • If it is not technically or functionally feasible to achieve the above U-values when renovating a roof, or a simple payback of less than 15 years cannot be achieved, then the insulation should be upgraded to the best level possible. 
  • Retained roofs are those that are already in existence but are being put to use above a new room, or a room that is being converted to a different type of use. 


The table below shows the U-values to be achieved by rooflights in various situations. As can be seen, these are generally not as stringent as before.
Tables_3_Part-L-2022.JPGHowever, there is now a requirement for any rooflight upstands built on site (not integral to the rooflight) to achieve a maximum U-value of 0.35W/m²K. This is a totally new requirement. 

Photovoltaic systems 

PV systems have now been brought into the Notional Building specification in Part L (England) 2021. The tables below show the criteria. 
Tables_4_Part-L-2022.JPG For more information, contact Paul Felgate on 01473 257671.