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INDUSTRY VIEWFINDER
the Fabric Energy Efficiency Standard (FEES), which was first brought into use with the Code for Sustainable Homes in 2010. FEES uses a whole-house calculation approach to set maximum limits on the energy demand that would normally be needed to maintain comfortable internal temperatures in a home. These are 39 kWh/m2
/year for apartments and mid-terraced houses, and 46 kWh/m2/year for end of terraced, semi-detached and terraced
houses. For a home to be ‘FEES-compliant’, the fabric must be of sufficient performance to ensure heating and cooling demand doesn’t exceed these figures.
One other key change with the new Part L, affecting contractors more than architects however, is the introduction of a regime of photo evidence submitted to Building Control, to demonstrate that the work on site is in accordance with the performance requirements specified in the architects’ design. This attempt to address the ‘performance gap’ is a step-change for many housebuilders; in the form of regular BREL (domestic) or BRUKL (non-domestic) reports proving construction rigour across projects.
U-values
Limits have been placed on U-values for windows and doors in new homes (tightened from 2.0 W/m2K to 1.6 W/m2K). Within the notional building model however, the U-value target for windows and doors is now an even lower 1.2 W/m2K – this was previously 1.4 W/m2K. Meanwhile a maximum of 0.18 W/m2 for walls has been instigated. Non-domestic U-values have been lowered too – 0.26 W/m2 for walls and 1.6 W/m2
over double the score recorded in our Industry Viewfinder a year ago (9%), but demonstrates that the upgraded Part L has rapidly become a familiar part of the range of parameters architects need to consider on new schemes. Overall the levels of architects responding to the survey in the ‘acceptable – very good’ group were broadly similar year on year, at 88% in 2023 and 89% in 2024.
However, in the category of respondents who believed they had for windows, to
produce at least 27% less carbon emissions in combination with other measures.
Heating, hot water & ventilation Under Part L, new and replacement heating systems (both domestic and non-domestic) now have to work with a lower maximum flow temperature of 55°C. Under Part F, dwellings must be ventilated with a minimum 0.5 litres of fresh air per square metre. The new Part O (designed to mitigate overheating), introduces limits on glazing for new-build homes (as well as care homes, schools and student accommodation) as well as new levels of cross-ventilation, presenting challenges for designers trying to maximise glazing for clients. Part L is split into Approved Document Part L1A, covering new
homes, and Part L1B, covering requirements for renovations and extensions to existing buildings. Part L1B requires raised fabric standards, including on extensions and conservatories, makes SAP applicable to extensions, and introduces a maximum U-value for replacement windows of 1.4 W/m2K. Roofs on extensions and conservatories should have a U-value of no higher than 0.15 W/m2K; refurbished roofs should have a maximum 0.16 W/m2K. Extensions’ walls have a maximum 0.18 W/m2 U-value, and doors, windows and rooflights on extensions are limited to 1.4 W/m2.
Comparing the stats: One year on Levels of understanding
The first question that we asked in the 2024 survey which directly replicated that ‘How would you rate your understanding of the new Part L, F and O 2021 in England?’
This question saw some interesting varieties of improvement on
2023, with those rating their understanding of the Part L updates this year as ‘very good’ making up 21% of respondents. This was
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a ‘Good’ understanding of Part L, there had only been a slight improvement, with 32% in 2024 believing they were at this level, compared with 28% in 2023. Also, perhaps slightly concerningly, there were 3% saying they had a ‘Very Poor’ awareness, when no respondents put themselves in this category in last year’s survey. This suggests that once the realities of Part L have bedded in, the complexities have been further revealed, or simply that not everyone is familiar with the requirements yet. The new, tighter Part F saw identical results in the ‘very good’ awareness’ category (6%), but the ‘good’ category was nearly double (17% to 32%). This was reassuring news that for ventilation requirements at least, architects had exponentially increased their familiarity in the preceding 12 months, given that arguably many Part F aspects are principally the remit of M&E engineers. (Despite this, 54% of our respondents said that in their projects, the architect was responsible for Part F compliance, whereas only 29% said it was M&E engineers, and 11% the contractor.) Those saying they were in the ‘acceptable’ to ‘very good’ category had increased slightly from 78% to 84%. And finally, for Part O, a brand new standard in 2022, and perhaps because of this fact, our respondents recorded an improvement in awareness year on year from 5% saying very good in 2023, to 8% this year. In addition, the overall amount saying they had an adequate or good level of awareness had risen from 69% to a healthy 73%.
EXPERT VIEW Chris Perry, senior architect at TODD Architects was an attendee at the Building Insights LIVE Round Table on Part L, F and O compliance hosted by Architects’ Datafile in May 2023, shortly before
the new regulations became mandatory. He has also kindly contributed his own insights for our Industry Viewfinder survey white paper, beginning with thoughts on how knowledgeable architects are required to be on the changes: “As we typically only work on large projects, we have MEP consultants take care of the Part F and Part O calculations, so we are slightly removed. We really just need to know the targets and the main principles; the calculation outputs sometimes seem like a magical art!”
Specific impacts of Part L
Despite positive results in the year since we last surveyed architects, in terms of their understanding of the new standards’ provisions, application of those standards depends on understanding the specific key changes brought in which could impact how they design buildings.
One key positive this year was that more architects perceived they had a better grasp of fabric aspects of reaching Part L’s 31%
ADF MARCH 2024
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