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INDUSTRY VIEWFINDER: A NEW ERA OF ENERGY EFFICIENT BUILDINGS
and ‘BRUKL’ for non-residential) represent a major change for housebuilders at least in showing comprehensive compliance including photographic evidence. However, they were only well understood by 23% of our survey respondents (rating themselves as ‘good’ or ‘very good’). By contrast, 31% said they had poor knowledge of them, suggesting that architects aren’t as engaged with this part of the compliance process as others in the supply chain.
The factor with the greatest understanding level was the new Primary Energy metric to be used as the measure of a building’s energy use (11% said they had ‘very good’ knowledge, however 44% said it was only ‘acceptable’). The carbon emissions target within Part L was well understood by 33% of respondents, and the FEES target by a decent 37%. Minimum fabric requirements were well understood by 48%, and the ‘notional building’ by only 30%.
The notional building is a relatively ‘involved’ concept but requires understanding due to its importance in potentially driving designs, but also its potential to create problems. Industry commentators believe there are issues with simply adopting the default values within the notional building, which is theoretically possible as a design approach to comply with the new Part L. The contention is that default values are formulated around energy loss, rather than a more holistic assessment of thermal bridging, and that if the ‘minimum temperature factor’ is not included, condensation and mould remain a risk.
Key Part L challenges We asked readers to rate four crucial areas within the new Part L framework on how challenging they were for designers. These were; the new U-values, the CIBSE TM23 method of air-tightness testing now adopted as the standard method by Building Regs, primary energy being the ‘Principal Performance Metric,’ and lastly, the use of the notional building. The ‘leading’ challenge picked by our survey respondents overall was the maximum U-values in Part L. A total of 60% of the architects and technologists we asked picked this factor as ‘moderately’ or ‘very’ challenging. Primary Energy being the ‘Principal Performance Metric’ received the same rating as the TM23 air testing method (67%) in terms of its level of challenge, and the notional building was cited as challenging by 61% of respondents. Overall, each of the four factors were rated as more challenging than not by our respondents, and many commented on the various challenges for the industry. ‘Cost’ was the stand-out factor in terms of being chosen as the
most ‘significant’ obstacle to overcome to achieve compliance with the new Part L. 66% picked it as a ‘significant’ barrier, and only 2% said it presented no difficulty. ‘Competency and quality of install’ was next, 52% saying it was ‘significant’ followed by ‘technical knowledge (34%) and ‘availability of suitable technologies’ (28%). An overwhelming 83% believed that the 31% emissions reduction
would be difficult to do in housebuilding, and not far behind was a 79% score for non-residential.
Part F Part F, covering the ventilation aspects of buildings guidance, is a fundamental adjunct to Part L, with the need for adequate ventilation becoming proportionally more important as buildings become more thermally efficient. While Part L tries to minimise air ‘infiltration’ through a wide range of air leakage paths in the building structure, Part F relates to ‘purpose-provided ventilation’ i.e. the controlled air exchange between the inside and outside of a building using natural and/or mechanical devices. If a building is designed with an air permeability level below 5 m3
(h/m2) , a fixed
amount of purpose ventilation – natural, mechanical or hybrid – is required under Part F. We asked our readers who in their experience was responsible for ensuring compliance with Part F – architect, M&E engineer, main contractor, or another party? Perhaps surprisingly, 54% of our respondents said that this was under the remit of the architect, whereas 29% said it would be the M&E engineer, and 11% saying the main contractor. The ‘other’ category was picked by 6%, with comments clarifying this may ‘depend on the contract,’ ‘could be a combination of all three,’ or could be an architectural technician, technologist, subcontractor or energy consultant.
Part O
This main intention behind the newly-introduced Part O is to limit excess solar gain in new build residential schemes, and remove the excess heat from the indoor environment. The new regulation breaks from previous Building Regs, by evaluating the overheating impact of designs on a room-by-room basis. The new regulation asks designers to pick a ‘simplified’ method of calculating the overheating risk on a building, versus a more complex ‘dynamic thermal modelling’ method. Understanding of the relative qualities of these methods for Part O compliance was poor among our cohort of architects and technologists – 75% said they did not have a good level of understanding.
Our respondents believed that they would be more likely to be asked to use the dynamic method to estimate overheating than not (63% versus 37%). The simplified method would however be called for by even more projects, according to 86% of respondents, with 40% saying it would be ‘always’ or ‘frequently’ used. Of our respondents, 37% (the top figure) said that minimising glazing in houses would be ‘very difficult,’ followed by 32% for apartment blocks. 32% believed that cross-ventilation to offset overheating would be ‘very difficult’ in apartment blocks. A resounding 81% said that avoiding mechanical cooling in apartment blocks would be difficult to some extent, and mitigating overheating in homes and apartment blocks would be ‘very difficult’ for 25%.
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ADF FEBRUARY 2023
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