Tracking the gap

The performance gap cannot be closed until designers and main contractors plot the emerging energy and emissions profile of their projects, says Dr Roderic Bunn, who introduces a new tool that aims to do just that

Everyone’s talking about operational net zero. It’s all over social media – LinkedIn is full of it, along with earnest corporate statements and institutional pronouncements of various kinds. All very worthy. Some of it may even be real. Those of us who analyse the outturn performance of buildings on a regular basis are rather more sceptical. Underperformance is still rife.

Yet the industry talks up net zero as if the performance gap has been closed. Yes, there have been much-needed developments, such as the RIBA Plan for use1 – the RIBA’s take on Soft Landings – and the energy-rating scheme for offices Nabers UK,2 both of which could be game-changers. 

On the other hand, such advances tend to be voluntary and/or too niche to make a huge difference immediately. Even a mature technique such as Passivhaus remains a minority sport in the wider construction game, a clear example of how a conservative, habit-obsessed, delivery-focused industry such as construction avoids doing anything it’s not contracted, regulated or insured to do. 

While these new developments are vital components of the net-zero equation, we don’t have decades for them to take effect. Arguably, we have months to achieve the rapid improvements in building performance needed on all projects – domestic and non-domestic.

We certainly can’t rely on a revolution in Building Regulations. In January 2021, the Ministry of Housing, Communities and Local Government (MHCLG) [now renamed the Department for Levelling Up, Housing and Communities] issued its low carbon vision for future homes and non-domestic buildings. It said it will ‘examine wider proposals for how to address the performance gap when buildings are designed and constructed, and improve the performance of buildings in operation’. Which is great – but the MHCLG’s proposed timeframe? 2025.3

The lack of urgency is baffling, until one realises that the ministry openly states that the much-maligned practice of design-for-compliance is only based on ‘anecdotal evidence’, despite revelations in the government’s own £8m Building Performance Evaluation (BPE) programme that the practice was endemic4. It’s largely stimulated by the Regulations and, therefore, cemented into employers’ requirements and contracts. 

So, what needs to be done to get project teams to track energy and emissions during procurement? First, there needs to be a major cultural reset: the industry – and its clients – must take custody of outturn performance. That requires professional responsibilities to extend beyond design and delivery and into initial building operation, no matter what the current Building Regulations require and what standard construction contracts stipulate. 

This necessitates a commitment to the Soft Landings approach of graduated handover, along with an obligation to conduct performance evaluation and feedback as a standard professional duty. As Chris Twinn says: ‘If [a] completed building fails to deliver on our predictions, the whole basis of Paris-proof zero carbon evaporates. No hiding behind some code-compliant prediction with the performance gap. Designers, constructors, and operators will be judged on the actual performance of the buildings they deliver.’5 

Absolutely. But as it stands, the objectives of Part L compliance-based modelling are very different from those of operational energy modelling. Dynamic simulation modellers employed to perform calculations against the National Calculation Method are not required to have expertise in building performance analysis. They are usually too detached from the project team.

They also often lack the experience to reflect the diversities and orders of magnitude that drive up a building’s operational energy consumption and emissions beyond the notional values used for regulatory compliance. Typical factors that may raise energy use by orders of magnitude include higher system operating hours (particularly outside of normal operating parameters), higher fabric air leakage than assumed at design, shortcomings in commissioning, and poor system control.

There needs to be a cultural reset: the industry must take custody of outturn performance

On top of all that, the duties under which energy modellers are typically appointed may not include detailed modelling until RIBA Stage 3: Spatial Coordination. If detailed modelling is required in RIBA Stage 2: Concept Design, concept options would need to be narrowed much earlier to enable a design team to generate robust calculations. That’s not the norm. 

For these reasons, the use of compliance models to benchmark in-use performance is inappropriate, and their general lack of use after a Building Regulation UK Part L report submission means opportunities for reductions in operational energy and emissions will be missed. For those opportunities to become known and potential improvement interventions identified, outturn performance must be visible to the whole project team at key points throughout procurement and delivery, not just during design. Assessments also need to be continued after handover so in-use performance can be compared against expectations of the final developed model. 

The emerging operational performance also needs to be made explicit and visible to clients, their advisers, and decision-makers, some of whom who may not be technically literate. An emerging energy-performance gap cannot be hidden in arcane numbers. It must be simple, clear and graphic, and, therefore, actionable. 

Help is at hand. As part of a project for the Centre for Digital Built Britain, host of Government Soft Landings6 (the central government equivalent of the Soft Landings Framework), the author and John Field, director of Native-Hue, have developed an Excel-based spreadsheet that aims to provide the functionality for assessment of operational energy and carbon dioxide emissions as a project progresses through delivery and into operation. Called the Operational Energy and Carbon (OpEC) spreadsheet, it is designed to track changes to power loads.

Until we start tracking operational energy as a norm on all projects and use that to inform sensible decisions, the vast majority of new and retrofit construction projects will persist in delivering less than they promise.  

I accept that many things have to change for compliance at design to graduate to compliance in use. Appointments, the contracts, the commissioning programmes, what constitutes Practical Completion (particularly its legal status), project insurance, payment regimes, and project budgeting all need an overhaul.

The structures we use at the moment for attempting to deliver a net zero asset – with regulatory sign-off at design – simply don’t work for ensuring performance outcomes, whether covered by guarantees or not.

Even if we manage to revolutionise compliance, clients also need to professionalise themselves. Their influence on ultimate outturn performance can be as great as that of a delivery team. Arguably, higher professional standards are needed for those who procure buildings. As the architect Bill Gething once said, construction has to become a privilege, not a right. It can’t remain a Wild West activity if net-operational zero is truly the ambition. 

The OpEC spreadsheet is available via CDBB.


  1. RIBA Plan for use guide (2021). 
  2. Nabers UK
  3. The Future Buildings Standard. Consultation on changes to Part L (conservation of fuel and power) and Part F (ventilation) of the Building Regulations for non-domestic buildings and dwellings; and overheating in new residential buildings. MHCLG. January 2021. 
  4. Palmer J, Terry N, and Armitage P (2016). Building performance evaluation programme: findings from non-domestic projects; getting the best from buildings. InnovateUK.
  5. Twinn C, The realistic route to zero-carbon. CIBSE Journal, June 2020.
  6. Government Soft Landings – Revised guidance for the public sector on applying BS8536 parts 1 and 2. DOI.

About the author
Dr Roderic Bunn is a building performance specialist, Soft Landings consultant and associate with engineering consultancy WMEboom