Reducing the gap

On Tuesday (8th July), I attended the Zero Carbon Hub’s launch of their ‘End of Term’ report on ‘Closing the gap between design and as-built’, which can be downloaded from here.  The presentations are available here.

 The overall aim of the project is that:

“from 2020, we should be able to demonstrate that at least 90% of all new homes meet or perform better than the designed energy / carbon performance”.

I’ve spent the last year and a bit involved in some of the workgroups which have helped develop recommendations and it’s been a fascinating experience. Amongst the evidence gathered, the project included in-depth studies of 21 sites volunteered by the house building industry. These revealed widespread shortfalls in performance when built, but also problems with the design and final energy assessment measurements and inputs.  As an example, on many sites things that should have been installed, weren’t, and things that shouldn’t have been there from the design stage drawings and specifications, were.

It appears that the various causes of the performance gap are systemic and deeply rooted in the industry’s working practices.

The three key contributory factors to the gap are: lack of knowledge and skills; unclear allocation of responsibilities, and inadequate communication. I’d recommend delving into the full report to look at the recommendations in detail, but I’ll outline just a few of the themes and recommendations and my thoughts on them below.

Energy Literacy

Training for everyone in the industry and coming into the industry should emphasise energy performance awareness, skills and knowledge, from site operatives through to planners, designers, procurement staff, assessors, testers and inspectors.

Quite simply, too many people involved in building new homes (not everyone), have only a sketchy idea of the effects of good design for energy efficiency. Many involved aren’t aware of the  importance of doing things correctly to minimise heat losses and fuel usage, and many energy assessors even don’t have an adequate understanding to be able to adequately advise clients who themselves may not know what constitutes ‘good’. The ‘Siteworks’ sections of our product literature includes ‘good practice’ guidance for achieving energy performance on site, which if followed can assist with better building practices, but this kind of information needs to be incorporated into the process, such that designers understand and incorporate it and builders follow it.

Improving Quality Output

Improve specification, design and procurement of materials and services: Improve manufacturer specifications and installation instructions to focus on correct installation of products and systems to achieve high levels of energy performance.

On top of the above, more can be done to assist designers and builders. A great example is the method statements, training programme and details produced to support Kingspan’s Internal Wall Insulation System – good practical guidance to encourage best practice installations.

Responsibility for the provision of ‘standard’ construction design details should be moved to industry control. This industry owned and maintained Construction Details Scheme should provide ‘assured’ as-built energy performance for the most common major fabric junctions and systems.

Government is obviously keen to relinquish responsibility to Industry for this one, so have announced some ‘pump-prime’ funding to get this started, but a lot of work will be required;  some improved standards and clarifications for thermal modellers are needed and some means to ensure that buildable competent modelled details come out of the process. Having good construction details and process sequences for products which do not have them will become very, very important as we get closer to carbon compliance levels. Just claiming to follow the ACD’s isn’t going to cut it!

An increased focus on energy-related checks and assessments is needed across all areas of the building delivery chain, from the design stage to completion on site.

Communication and quality assurance through the process certainly needs tightening and improving.

National Compliance Method and Regime

Comprehensive Product Specific Plain Language Compliance Report, with a signed declaration of accuracy of the input information by the housebuilder, to be provided to Building Control at design stage and updated at as-built stage again signed off by the housebuilder before the EPC can be produced.

This boils down to better information in the energy assessments – which we’ve been doing in-house for years, so that the information in the assessment is based on full specification information, not just  ‘Wall 1’, ‘Wall 2’ etc. This also introduces a better ‘closed loop’, so that the housebuilder acknowledges the energy assessment more and takes ownership – they after all are the one’s responsible for complying.

The accuracy of U-value and Psi-value calculations needs to be improved by: Improved training and quality assurance for those undertaking U-value calculations and those undertaking Psi-value calculations.

As it stands at present, the majority of people undertaking U-value calculations across the industry have no, or very little training and minimal or no quality control of the calculations they produce. Competent U-value calculations is something we’ve been involved with and pushing for, for some time now. We have been involved in the BBA/TIMSA set up U-value competency scheme since it’s launch and I’ve raised many times that it is fundamentally important that all of the inputs that go into energy calculations be competently derived, based on correct application of methodologies and conventions (which themselves need to be updated and reviewed regularly).

Undertake a systematic review of SAP methodology and assumptions, particularly focusing on those inputs which have significant impacts on the Performance Gap.

This one ties in to another of the recommendations, which is:

SAP default values should be reviewed to ensure they are worst case to encourage product / system specific values to be entered.

Worst case defaults ensure that poor information is compensated for by tighter design, this helps to encourage designers and builders not to use those defaults, but to actually consider better performing, tested alternatives.

One of the worst areas for this is thermal bridging in SAP. The default for a dwelling as a whole (y=0.15) isn’t as bad as the defaults for individual junctions would come out (more like y=0.21 for most houses if default psi values and actual detail lengths were used to calculate an equivalent y-value) and in any respect, the Approved Design (ACD’s) column in SAP, (which 80% of the industry seem to be claiming, whether or not there actually are any ACD’s for their chosen build type), has not been updated to reflect more stringent, better build practices, so the values are incorrect for how we build now and how we will build going forward.

Confidence (or ‘in-situ’) factors should be considered for evaluation to reflect the real performance of the system or combined elements (i.e. the performance of a specific make up of completed walls or entire heating system, including its controls, etc.) implemented in such a way to allow competing systems to innovate and demonstrate their specific as-built performance.

This is one that I’m in two minds about,  I think that real performance is likely to differ from that calculated, primarily due to issues with either the calculation, or arising from the on-site construction and workmanship and if both the calculation is correct and the build are right, then the conventions, or the maths behind the calculations likely needs looking at and changing – rather than patching up the energy assessment with a confidence factor.

I’m not a fan of confidence, or ‘fudge’ factors

That said, it would appear that in-situ, as-built performance of systems and constructions  does need to be looked at further, so a programme of evidence collection and better testing methods may well be needed to help identify any issues of possible underperformance.

Overall there are a lot of good suggestions in the report about things that can and should be improved upon for the whole process of designing and building new dwellings. The question becomes whether there is sufficient will to make some solid progress towards improving things.

I’m sure that those committed to the journey, will try and raise standards and reduce the gap. Those that don’t however may carry on with business as usual, and ultimately for them, some kind of stick from government is likely to be needed…

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Jon Ducker is a qualified energy assessor working for Kingspan Insulation Ltd. He has an extensive knowledge of energy efficiency, renewable energy systems and sustainability in buildings with an expert knowledge of the relevant sections of buildings regulations and standards and their interactions with SAP. He provides authoritative advice regarding energy assessments for a wide range of public and private sector clients.

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