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Bridging the gap: Post-occupancy evaluation

The glaring chasm between predicted and actual CO2 emissions is under the spotlight. Martin Spring looks at the latest initiatives. llustrations by Hanna Melin

Enric Miralles’ Stirling Prize-winning Scottish Parliament Building was praised for its reliance on natural ventilation and attained the second-highest B rating in its Energy Performance Certificate, based on predicted loads in 2009. But actual energy consumption recorded in 2008/9 was 293kWh/m2, or 2.3 times that indicated in the certificate.

This is nothing new. A similar phenomenon emerged from a recent survey of university buildings. In an analysis compiled by the RIBA/CIBSE online tool CarbonBuzz, the median building of the group was predicted at design stage to emit 25 kg/m2/year of carbon dioxide, whereas after occupation its actual emissions had escalated more than sixfold.

83: Percentage of carbon emission increased from leaving equipment on overnight in schools

The glaring gap between forecast and actual CO2 emissions shown in these examples is the rule rather than the exception. It is not the result of wrongly predicting the performance of standard building and services elements to comply with assessments such as Part L and Energy Performance Certificates. It’s what the designers leave out that causes the problem. These unregulated uses include energy-hungry items like server rooms and catering facilities. Not accounting for abnormal occupancy levels and operating hours can also skew calculations.

In the UK, the doyens of post-occupancy evaluations are Adrian Leaman and Bill Bordass at the Usable Buildings Trust and Fionn Stevenson at the Low Carbon Building Group of Oxford Brookes University. Leaman covers occupant behaviour and management practices, while Bordass looks at building services, energy and environmental design. And Stevenson argues that POEs have ‘an enormous and essential role’ in saving carbon emissions through improved building performance. ‘You wouldn’t drive a car without giving it an annual MOT and service, would you?’ The equivalent for buildings, she explains, is to ‘diagnose’ them in a progression of increasingly lengthy and intensive investigations. She rejects the term ‘post-occupancy evaluation’ in favour of ‘building performance evaluation’.

223: Completed buildings and design projects on RIBA/CIBSE online database CarbonBuzz so far

‘You can-fine tune a building design as much as you like, but unless you consider how the occupants use the building you won’t get far,’ she continues. ‘User behaviour can result in variations of up to 300 per cent of energy usage. So you’ve got to take the hard data of building performance records and the soft social data of how people use the building and cross-relate them.’

In a recent study, ‘Energy Performance of Schools’, Max Fordham Consulting Engineers pointed the finger at the accumulation of PCs printers, photocopiers, interactive whiteboards and plasma screens. ‘In many of the 15 schools we visited, equipment was left on all the time,’ the study found. ‘This can increase the carbon emissions of the building by a massive 83 per cent.’

£8m: The grant given for 20 buildings to be evaluated over a two-year period

Since 2008, all public buildings – some 45,000 of them – are required by law to publicly exhibit Display Energy Certificates revealing actual energy consumed. The UK-GBC has recently launched a task force to look at how the current quagmire of Energy Performance Certificates, DECs and the Carbon Reduction Commitment can be simplified. Alan Shingler, chair of the RIBA’s Sustainable Futures Group, is one of many industry professionals who has called for DECs to be rolled out on all buildings.

Since its database came on stream in 2008, CarbonBuzz has expanded it across all building types so that it now encompasses a total of 223 design projects and completed buildings. In nearly every case, median design data undercuts the CIBSE benchmark while median completed building data overreaches it.

How then can architects and engineers get a more realistic grasp of these issues at the design stage? Arguably, the only answer is through monitoring and by feeding this evidence back into the designs and construction of comparable buildings. But there is also the thorny question of who pays and how to share this information without making a client and project team look bad. Even if a building is not named, it could hardly escape identification from publication of an in-depth examination of how it performs and why.

There are some encouraging signs that the industry is facing up to the reality that monitoring is the only way to make real progress in lowering carbon emissions. Last December, 20 lucky completed buildings won grants totalling £8 million for exhaustive post-occupancy evaluations over a two-year period.

The nine domestic and 13 non-domestic buildings awarded research grants include five schools by Aedas, two schools and an HQ by Feilden Clegg Bradley Studios, a children’s centreby Architype and Crawley Library by Penoyre & Prasad. Those for housing cost £50-60,000, because of the heavy monitoring required. The grants were awarded by the government-backed Technology Strategy Board, which has invited tenders by 13 April for a new grants.

Costs can be significantly reduced if an initial survey is undertaken to see if there is a problem, and then target monitoring accordingly. A preliminary trouble-spotting survey can be carried out, Stevenson suggests, by little more than a walk-through by a suitably qualified assessor – in the company of the design team and occupants – armed with energy use and data, followed by a quick questionnaire.

The Low Carbon Building Group (LCBG) is currently 18 months into a two-year research programme into 10 buildings designed by Architype. ‘POEs are traditionally undertaken three or five years after a building is completed,’ explains LCBG research associate Lisa Pasquale. ‘But by then technology has moved on and the building is obsolete. So our feedback loop is much quicker and allows adjustments to the building as it nears completion and handover.’

Pasquale’s evaluations are tied in with another initiative called Soft Landings that was devised by architect Mark Way with the Usable Buildings Trust and the built environment research organisation, BSRIA. In Soft Landings, the project team holds the hand of the client at the period of occupation. The aim is to fine-tune and de-bug systems and help the occupiers get to grips with their new building.

Are we now at the dawn of an age when all new buildings will be subjected to performance evaluations and real evidence is fed back into new designs? Sadly, not, as Mark Kowal, partner at Sheppard Robson says, ‘We try to do it on every project, but we’ve only managed it on five or six. Most office tenants are reluctant to give out that information and pay for it.’

Both Feilden Clegg Bradley Studios and Architype have sunk their own money into performance evaluations. Architype contributed £55,000 into LCBG’s £140,000 two-year project. ‘This investment has proved to be more valuable than we thought,’ says Architype partner Jonathan Hines. ‘The return has been to improve the building and our service for the client. So why doesn’t every architect do it?’

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