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Measuring building performance is the only way to learn sustainability lessons

Words:
Peter Fisher

Post occupancy evaluations have given Bennetts Associates some perhaps surprising answers to its quest for sustainable design by 2030

The headquarters for Wessex Water (2001) in Bath achieved the highest ever BREEAM rating for a commercial office building at that time and became a national benchmark for sustainability in the early 2000s. But it also taught Bennetts a lot about fine tuning a building with its users.
The headquarters for Wessex Water (2001) in Bath achieved the highest ever BREEAM rating for a commercial office building at that time and became a national benchmark for sustainability in the early 2000s. But it also taught Bennetts a lot about fine tuning a building with its users. Credit: Peter Cook

Lessons learnt from previous projects have always been invaluable to current work. This is especially true now, as we confront the challenge of building for net zero carbon by 2030.

We can only properly understand how demanding and feasible the emerging net zero carbon targets are by referring to actual benchmarks drawn from completed projects. However, one of the most persistent challenges in the built environment has been obtaining robust data on how buildings perform. It was for this reason that the UKGBC’s very first campaign, following its foundation more than 10 years ago, was for ‘real data’.

Ever since forming more than three decades ago, Bennetts Associates’ has striven to create architecture with the lightest environmental footprint. We have long believed this can only be achieved if the aspirations of projects are supported by hard data and clear benchmarks, as well as understanding the response of the people that use them.

It was to this end that in December last year our whole firm re-visited Wessex Water’s operations centre in Bath, a project we completed 20 years ago. The CPD day was to reinforce the importance of learning from previous projects and the value of verified quantative data, especially when viewed alongside a building’s spatial and material qualities. On its completion the project underwent three years of post-occupancy evaluation (POE), which revealed much about how it was performing and how it could be optimised. Some issues were physical in nature, such as junctions between cladding and roofing, which were better sealed. But most were more managerial and human in nature. The facilities management team learned to play the instrument, and energy performance settled to be within the briefing targets.

To mark the 20th anniversary of its completion, we and BuroHappold have once again carried out POE to see how the building is performing today and how it might compare with emerging net zero carbon energy targets. By and large the building is unaltered. The boilers have been replaced and some PV has been added. But otherwise it is much as it was. Its energy performance today is such that if it was switched to all electric operation using air source heat pumps, then it would meet the UKGBC’s net zero carbon operational energy targets for office buildings. The council’s target for 2025-30 is 90kWh/m2/a, which could be achieved if the heating was switched from gas boilers to heat pumps and the electricity bought from renewable sources.

Simple lessons

A key lesson from Wessex and other projects is not that we need to radically change how we design buildings, but rather that we just need to do things well. The project is almost entirely naturally ventilated, with good daylighting and lots of exposed thermal mass – strategies that remain every bit as relevant today. Australia’s NABERS system – which has helped to significantly reduce energy consumption in both new and existing buildings – has shown that the biggest improvements are usually to be found through simplified controls and the better management of buildings, rather than innovative technological change.  

  • Atrium of Bayes Centre (2019) for academics and students working in the fields of Data Technology, Design Informatics, Maths and Robotics with industrial collaborators at the University of Edinburgh. The second phase was informed by a full post occupancy study.
    Atrium of Bayes Centre (2019) for academics and students working in the fields of Data Technology, Design Informatics, Maths and Robotics with industrial collaborators at the University of Edinburgh. The second phase was informed by a full post occupancy study. Credit: Keith Hunter
  • Energy Intensity for offices with several Bennetts Associates’ project plotted using UKGBC Science Based Targets methodology.
    Energy Intensity for offices with several Bennetts Associates’ project plotted using UKGBC Science Based Targets methodology. Credit: Bennetts Associates
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NABERS binds the design modelling of energy to actual performance. In the UK we have always tried to get energy modelling to be done using CIBSE’s TM54 methodology, though it is a greater workload for service engineers, which has limited uptake. What TM54 brings is clear guidance for evaluating operational energy use more fully, and accurately, at the design stage. Important one would think. It is thought likely now – at least in the commercial world – to be superseded by Design for Performance. This is being trialled on one of our projects and is leading to much better early stage modelling, together with verifiable in-use performance. It is the result of a memorandum of understanding between the UK’s Better Buildings Partnership and NABERS and is bringing to the UK a design for performance rather than compliance approach.

Looking beyond operational energy

There is of course much more to sustainability than operational energy. In part motivated by an ambitious brief written by environmentalist Jonathon Porritt, Wessex Water was the first project where we also started to look in detail at environmental issues beyond operational energy, adding embodied carbon, water use, construction transport, construction waste, and biodiversity. These in turn led to the Movement for Innovation sustainability indicators. Instigated by Rab Bennetts and with data compiled by BRE, these resulted in simple wind-rose diagrams, which are still referred to today (the RIBA 2030 Climate Challenge targets use the embodied energy data for example). Ever since then we have collected as much data as possible on those indicators. The dataset has helped to bring confidence in the setting of challenging, but feasible, targets for project briefs.

Even for just six indicators though, data can be hard to come by. Often our main method of obtaining it is no more sophisticated than doggedly asking for it. A proforma for key standards and data is embedded into each project brief and then reiterated in workstage reports, specs, and record information, as well as follow up POE studies. Such data now being included in RIBA awards submission will hopefully drive common metrics that are more widely understood and consistent.

There is no replacement for a full POE study where possible, however. When Potterrow in Edinburgh won the RIAS Doolan Prize, the money was used to fund a detailed report by Bill Bordass at Building Use Studies (BUS). Lessons from the results were then fed into the detailing of the second phase of the project. Having commissioned a number of such studies, we are now a licensed BUS partner so can undertake a greater number of these in house using the BUS methodology.

Importantly, the methodology includes surveys of occupant comfort and perception. In our quest to reduce energy use and carbon emissions we must not lose sight of the human and experiential qualities of architecture. This last point cannot be overstated. Buildings use the least energy when people are comfortable.

One of main lessons learnt from completed buildings is that the more complex a building’s mechanical systems and associated controls are the more energy it will use. A key conclusion is that sustainability is not a technological solution applied to architecture, but rather is something at the core of what architecture is.

Peter Fisher is a director at Bennetts Associates

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