12 COMMENT


CLOSING THE GAP ON PERFORMANCE


Dr Gavin Dunn, chief executive of the Chartered Association of Building Engineers (CABE)


Dr Gavin Dunn from the Chartered Association of Building Engineers (CABE) says there is still a ‘performance gap’ between the design of buildings and how they actually perform once built, and looks at how to tackle the issue.


designed and as-built building performance. From energy performance, air quality, ventila-


T


tion and wellbeing, how can we improve buildings and ensure we are getting the best- performing buildings both now and in the long-term? The latest journey of improving the energy


RESEARCH SHOWS THAT ON AVERAGE UK HOMES ARE LOSING 60 PER CENT MORE HEAT THROUGH THEIR FABRIC THAN WOULD BE EXPECTED


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performance of new build housing began 13 years ago in 2006, when we saw a significant tightening of energy efficiency requirements within the Building Regulations with a shift to targeting carbon emissions. Subsequent step changes in both 2010 and 2013 related to the way we approach calculating and presenting energy compliance. Since then, we have clearly changed the performance of new homes — but there have been unintended consequences that we need to acknowledge, be open about and to fix before we can continue on this journey. While air quality and overheating are unintended consequences of this, the perform- ance gap in energy usage between building design and operation is one of the key underly- ing challenges of the industry. It has been a well-known issue and acknowledged by Government since 2012, but sadly we haven’t seen any meaningful improvements in that time. The UK is building more homes, but if we are going to be zero carbon and fully committed to removing traditional fossil fuel heating systems in new homes by 2025 (as per the Future Homes Standard 2025) then now is the time to fix it. There are a few elements to the performance


gap, in terms of compliance predictions and modelling, and the actual operational building use. There are the ‘known knowns’ which we understand. The energy models make various assumptions and estimations in terms of the way they work, and while there is a method in place to improve the models over time, to a greater extent these calculations do not appear to be a fundamental area of concern because they are well understood, and because within the regulatory process we only ever compare results to other modelled results calculated in


he construction industry has long grappled with the challenges of closing the performance gap between as-


the same way. Any inaccuracies will therefore cancel each other out. The ‘known unknowns’ – or rather, the unreg-


ulated unknowns – are the differences between what we design and the reality. These are the standard occupancy patterns and assumptions made about how a building will be operated and used, which inevitably differ from how each individual building is actually used by real people (i.e. people all operate their houses differently). This is similar to the ‘standardised driving’ conditions used in MPG tests on cars. There are also known gaps for which we should not be overly concerned with as we cannot do anything about the fact that people will always use buildings differently. The most significant area of concern is what I


refer to as the ‘unknown-unknowns’. Research suggests that even when we account for the ‘known knowns’ and ‘known unknowns’ there is still a significant gap between what we design in the models and how buildings actually perform once built. This excess energy use can only be as a result of product substitution on site, poor detailing, and build quality.


FABRIC FIRST It would appear that in new UK housing a major factor is the building fabric, particularly as we start to move away from certain fuel types such as natural gas and other fossil fuels which have a very high carbon impact. The decarbonisation of domestic heating and the progressive shift to electric heating will present its own set of


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