Building surveying: energy performance

Mind the gap

14 February 2014

Eimear Moloney looks at the technical and behavioural reasons behind higher than predicted energy use in buildings

The term 'performance gap' was coined by the construction industry to label the difference between the predicted and the actual energy consumption of buildings. And it is huge. CarbonBuzz quotes real energy use at 1.5 to 2.5 times higher than predicted. So what is going wrong and what can be done about it?

As can be expected, there is not one single answer. But in broad terms the energy performance gap is caused by anomalies that fall under one of two headings; technical and behavioural.


The technical issues can be attributed to the functioning of the mechanical and electrical systems within a building and can, in the majority of cases, be analysed by investigating the building management system (BMS). It should also be noted that in some instances, what is attributed to technical issues can be more to do with how the energy predictions were made.

For a period it seemed that some were using Building Regulations Part L compliance results as energy predictions when, in fact, not only are these unsuitable but they were never intended for this use.


Behavioural issues are generally more complicated and difficult to predict, ranging from how occupiers use their heating and cooling controls to how the building manager has set up the maintenance routines.

What can be done?

Of the numerous industry initiatives to help reduce the performance gap, probably the most well-known and a good catch-all is the BSRIA Soft Landings framework. This is a methodology for the briefing, design and handover of buildings that aims to smooth the transition from construction to operation and use. Central government has chosen to adopt Government Soft Landings, which is a similar framework. Some developers are favouring energy performance contracting, and the BREEAM New Construction 2011 guidance recommends a series of aftercare measures.

Perhaps the minimum that should be done is to extend building design contracts beyond the 12-month defects period. BREEAM and BSRIA Soft Landings recommend that designers' involvement should be three years post-handover. The benefits are evidenced in numerous case studies and it is likely that the additional cost to the client will be written off against the energy savings made. If energy use is 1.5 times greater than predicted, then the potential to save is huge.

The activities undertaken during the extension of contracts could take in those listed in the BSRIA Soft Landings document, which include various site visits and reports. As a minimum they should:

  • analyse and interrogate the BMS on a regular basis
  • review how the building is being used through a building user survey or a building performance evaluation and, most importantly, react to the findings
  • retrain the building or site manager in how all the systems work – it is likely they will have forgotten.

All of the above are easy to include in a standard contract and, added to an improved level of user training at project handover, will ensure that any new building will be on its way to a significantly reduced performance gap.

 Case study

A 68-bedroom student new build hall of residence was completed in 2011 and a building energy optimisation investigation began in 2013. One of the central areas of focus was the domestic hot water system, which included a combination of solar hot water and gas-fired water boilers. Following a series of optimisation exercises to the building management system, the solar system performance has increased, allowing the gas boilers to do only the minimum amount of work.

Eimear Moloney is an Executive Engineer and Performance Specialist at Hoare Lea

Further information

Related competencies include: T051