Among the usual flurry of work before the winter holidays, there was one discreet email that we had to pause for.

It was a short message from the BRE to British Land and the 1 Broadgate team, informing us that the project had formally received its NABERS UK ‘Design for Performance’ (‘DfP’) target rating certificate, for five stars. The first building in the UK to register, it also received a notable DfP0001 registration reference.

NABERS UK ‘DfP’ is an approach for

• predicting energy consumption as accurately as possible during the design life of a project,
• reducing predicted energy use through design and specification decisions, and
• preparing the building for accurate energy monitoring throughout its operational life.

Very importantly, it is third party certified and holds the applicant to account. It was launched in the UK in November 2020 by the Better Buildings Partnership and is a very important process for buildings with a Net Zero Carbon brief.

When complete in 2025, 1 Broadgate will create some of the most sustainable mixed-use space in London. And as early adopters of the NABERS rating, British Land are able to demonstrate a sustainability commitment that extends well beyond this date. As the project’s development continues at pace, we wanted to reflect on the project’s sustainability journey to date and the path we are setting out for the important steps to come.

The brief should exceed current standards

1 Broadgate registered as a NABERS UK Pioneer Project during its RIBA Stage 3, but British Land had already devised a plan for earlier design stages. In a short period of time we switched from the existing standard - CIBSE’s Technical Memorandum 54 ‘Operational Energy Performance’ - to a British Land-commissioned bespoke method named Enhanced Building Energy Modelling in anticipation of NABERS UK, which was still being piloted at the time. The switch to NABERS UK was also a pre-requisite of Jones Lang LaSalle (JLL), who were the first occupier to sign an agreement for Lease.

Opportunities were therefore identified early, and as soon as the NABERS UK scheme was formally launched, 1 Broadgate was ready to commit to a high target energy rating. As obvious as it may sound, an ambitious brief is of vital importance to a sustainable and future-ready project. Setting this high standard from the start has allowed 1 Broadgate to adapt its ambition to one of the most rapidly changing markets in recent years.

Modelling in detail is rewarding

One of the first models for predicted energy consumption for 1 Broadgate showed a predicted energy consumption that was just below the NABERS UK 5.0* rating upper limit (70 kWhe/m²), which in 2020 the UK Green Building Council established as the interim Net Zero Carbon target for base buildings completed between 2025 and 2030.

The UKGBC target tightens to an upper limit of 55 kWhe/m^{2 NLA} from 2025 and then 35 kWhe/m^{2, NLA} from 2035, a pretty significant jump in practical terms. Design development, further modelling and independent reviews took 1 Broadgate’s predicted energy down to a NABERS UK 5.5*rating, well in advance of the UKGBC’s interim timeframes. The certified target rating of 5.0* includes a recommended contingency to cover for unknowns and market inexperience, but these are the very risks that have been framing the conversations with a number of stakeholders since, including the future occupiers, JLL and Allen & Overy, and principal contractor, Sir Robert McAlpine.

The opportunity to reduce the predicted energy is unlikely to have been possible with a simpler method of simulation and analysis. The energy model helped us see opportunities and justify design changes. We introduced heat pumps and thermal stores, optimised the size and operation of plant, recovered more energy, refined controls and challenged elements of energy wastage. The NABERS DfP method requires the simulation model to test and report on various situations that could affect energy consumption, for example poor operation, poor maintenance and extreme weather.

If you are aiming for Net Zero Carbon, it is worth the jump to a NABERS UK level of predictive modelling. Without it, you may not have a building and systems that are robust enough to operate under future market expectations. Furthermore, the government is likely to introduce a new energy disclosure framework to offices >1,000m² this year. Consequently, the market value of lower energy meter readings is expected to increase rapidly over the next few years.

Peer reviews can reduce predicted energy and provide a fresh outlook

Part of the NABERS UK DfP process is an Independent Design Review (IDR), a formalised step that not only checks the assumptions and energy prediction calculation, but also interrogates and makes constructive suggestions. From our experience, both as reviewers and reviewees, this results in a very healthy discussion, after which either energy consumption is theoretically reduced or risks are actively addressed.

The 1 Broadgate development, as a Pioneer Project, had no less than three IDRs, including a review of our 3D and systems model. A typical project would not need as many reviews, but there are clear benefits to having at least two sessions especially in the early years of the scheme: one to check that design is heading in the right direction and has captured all opportunities, and another before the project is procured to ensure that the main contractor tender includes a clear intent.

Involve the end-users, indefinitely

For years the industry has been contemplating ‘soft landings’ (a gradual and informative handover of a building to end-users) but never applying it properly. NABERS dropped in and changed that, almost overnight. The NABERS base building energy rating is so reliant on tenant installations and behaviour that it is not only necessary but also highly beneficial to involve end-users in the energy conversation as early as possible.

1 Broadgate was pioneering in setting up a Sustainability Working Committee involving British Land, their commercial tenants, the contractor, the project manager (Gardiner & Theobald) and ourselves (Hilson Moran); environmental engineers and sustainability consultants. At some point during the NABERS UK DfP process, tenant teams are required to share detailed fit-out information to be included into the energy model for a final predicted rating (at Practical Completion). Therefore discussing occupier needs, their intent on design and operation, etc and feeding back on the positive and negative impacts of energy/carbon adds a lot of foresight and opportunities to collaborate and improve before it is too late.

Collaboration with end-users is a win-win situation. Where the developer is also the landlord, this is also an opportunity to forge a strong relationship with a long-term customer.

Contractor obligations

If the process described so far were not constrained by the parameters of contracts, procurement, contingency, risk, etc., central building systems would continue being refined and optimised for a longer period of time, in reaction to details coming in from occupiers. However, tenants and their designs may be unknown or they may change in the future; but building services need to be bought on schedule. Programme delays have various implications and occupier behaviour is ultimately extremely difficult to predict.

For these reasons and more, elements of design have to be ‘frozen’ and a line drawn on base build improvements during early construction. On the one hand, central systems should be designed to be flexible and robust enough for whatever may be thrown at them, while operating at maximum efficiency for the greater proportion of their use. On the other hand, late design changes can have serious cost and programme consequences.

If a contractor has signed up to delivering a NABERS star rating but tenant design is making that rating look better or worse, the levels of responsibility and obligation could become blurred. Even where betterment is the intention of all parties involved, the DfP outcome can only be confirmed at Practical Completion.

It is recommended to run a model in parallel without tenant layouts, in order to fix a scenario at Practical Completion that is comparable to contracted delivery obligations, e.g. using tendering stage assumptions.

We are currently already in discussions about extended aftercare and the role of SMART technology in reacting fast to energy over-use. There is still some way to go and a lot more to learn. We hope to continue to share and contribute to better buildings along the journey.

Hilson Moran are interdisciplinary consultants, engineers and advisors, applying progressive thinking to shape the environments we live in.