Performance gap between building design and operation

There is significant evidence to suggest that buildings do not perform as well when they are completed as was anticipated when they were being designed. The difference between anticipated and actual performance is known as the performance gap.

Findings from studies such as PROBE (Post Occupancy Review of Buildings and their Engineering) which assessed 23 buildings previously featured as ‘exemplar designs’ in the Building Services Journal between 1995 and 2002, revealed that actual energy consumption in buildings is often twice as much as predicted.

More recent studies have suggested that in-use energy consumption can 5 to 10 times higher than compliance calculations carried out during the design stage:

• The Zero Carbon Hub Closing the gap between design and as-built performance, Evidence review report.
• Innovate UK's Building Performance Evaluation Programme.
• The Carbon Trust‘s Closing the gap, Lessons learned on realising the potential of low carbon building design.
• Carbon Buzz, Performance gap benchmarking data.

Studies such as these suggest that factors contributing to the performance gap include:

• A lack of monitoring and feedback following occupancy, meaning that problems are rarely identified, user behaviour is not corrected and lessons are not learned for future projects.
• Design assumptions do not properly reflect the in-use performance of buildings.
• Designers are rarely required to predict actual in-use energy consumption.
• Calculations for regulatory compliance do not account for all energy uses in buildings. These calculations are commonly misinterpreted as predictions of in-use energy consumption, when in fact they are simply mechanisms for complying with the Building Regulations.
• Unregulated sources of energy consumption such as small power loads, server rooms, external lighting, and so on are rarely considered at the design stage. Yet these typically account for more than 30% of the energy consumption in office buildings.
• The lack of guidance for modelling unregulated energy loads makes it difficult for designers to consider these at design stage.
• There are discrepancies between design specification and the specification and quality of works as-built.
• There are incorrect assumptions about the performance of some building components (such as party walls).
• There are rarely any consequences for designers, contractors and suppliers when energy consumption exceeds predictions.
• Project participants struggle to communicate the intended energy performance for the design from the earliest stages, and have ongoing problems with communicating the design intent throughout detailed design.
• There is poor feedback from site about what is, and what is not buildable.
• Site practices that may have been acceptable 20 years ago, no longer meet the required standards.
• There is an absence of engineering rigour around the design and installation of the services.

NB: In November 2015, BSRIA announced that it would back a four-month feasibility study to develop a prototype UK scheme intended to deliver the standard of energy performance specified in client briefs by adopting a ‘design for performance’ approach, first pioneered in Australia. See BSRIA support study into Australian solution to performance gap for more information.

[edit] Related articles on Designing Buildings

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• Building performance evaluation programme.
• Building performance metrics.
• Building regulations.
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• Closing the gap between design and as-built performance.
• Co-heating test.
• Code for sustainable homes.
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• Energy performance certificate.
• Energy Savings Opportunity Scheme.
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• Green building.
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• Mind the (performance) gap.
• Performance.
• Performance of exemplar buildings in use: Bridging the performance gap FB 78.
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