Bridging the performance gap

Visitors to Ecobuild last week will have heard a lot about the “performance gap.” It was all over the programme, the gap between the energy a building is designed to consume and what happens when it’s constructed. Note this is about “as-built” performance and doesn’t allow for what happens to energy use when a building is occupied. This is more than an issue for individual owners and users. If Government and other agencies rely on predicted performance figures to measure progress on energy efficiency and carbon reduction, they are likely to be working with flawed data.

The Zero Carbon Hub has been looking at the performance gap in house building and has found that some new homes are using 300% more energy than they were designed to.

Its latest report identified 15 priority issues – ones with a strong supporting evidence base and medium to high potential impact on the performance gap. These priority action issues include:

  • Design teams are not sufficiently aware of the implications of early stage decisions on energy performance
  • Different aspects of design, in particular building fabric and services, are not being properly integrated
  • Procurement teams do not prioritise energy related skills when selecting contractors, resulting in site teams that lack the knowledge to properly install services and fabric
  • Products with energy performance different to the intended design are being used on site without being fed back to the design team
  • Building services are being incorrectly installed and poorly commissioned

Speaking at Ecobuild, the DCLG’s Deputy Director, Building Regulations and Standards, Bob Ledsome said the issues identified by Zero Carbon Hub could apply equally to non-domestic buildings.

One panellist at Ecobuild used a common analogy to explain why buildings do not always perform as designed. He said it was like a car engineered to give a particular fuel consumption that returns widely varying mpg depending on how its driven. But in the case of as-built energy use we have a car that doesn’t perform no matter who is driving!

Looking at the (even wider) gap between design and in-use performance, BIM and Government Soft Landings guru Rob Manning says there’s a gap because the worlds of construction and operation don’t meet. Clients don’t always articulate what they want and operators aren’t engaged early enough and often enough. Manning also thought non-completion penalties could compromise commissioning and handover.

Smarter construction and intelligent customers can close the performance gap said Balfour Beatty’s Nick Pollard but at the moment customers value a £50k saving or two weeks off the programme more. A quick win is to revisit complex buildings, re-tune them and train the people that use them, he added.

The materials and technology on display at Ecobuild are truly impressive. The construction sector clearly has the tools to deliver better building performance but something is going terribly wrong. If your new car let out heat and let in water you’d conclude it wasn’t fit for purpose. Most buildings are of course constructed rather than engineered but clients must demand more, articulate what they want and spend the time (and yes the money) on commissioning, handover and tuning.

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