NABERS UK Interview with Yorgos Koronaios
In this interview with Yorgos Koronaios, Associate Director, Sustainable Design at Savills Earth shares his recent experience into pursuing NABERS UK, the lessons learnt through the assessment process, and how the retrofit of the building helped the project team deliver carbon reductions through different design features.
The B100 project involved multiple retrofit options (internal only, back-to-frame, vertical extension, new build). How did you approach evaluating these different options from a sustainability and project management perspective?
To clarify, when Savills, the sustainable design team, became involved in the B100 project, the business case had already been made to pursue a back-to-frame retrofit with an extension. We joined during early Stage 2 of the design process, focusing on design optimisation, balancing façade design, fabric performance and HVAC strategy with operational and embodied carbon reduction, as well as Net Zero alignment.
At this stage, we evaluated the back-to-frame option through embodied carbon and whole-life carbon assessments, comparing it with a potential new-build scenario. Although we were not involved from day one of the project, our analysis provided the client with additional confidence that the back-to-frame retrofit was the right direction for the B100 development.
How did the decision to pursue a back-to-frame retrofit achieve the 31% embodied carbon saving compared to new build, and how would you quantify these savings?
The design approach was performance-led from the outset. The existing building had challenges, including a high glazing ratio that had not been optimised. Starting from a back-to-frame position allowed us to rethink the design while retaining key structural components.
Discussions considered demolishing parts of the building and introducing a new structural frame, either concrete or steel, while supporting a vertical extension. Ultimately, a lighter steel frame was used to support the new upper floor.
Retaining the existing structure and foundations provided a significant advantage. Structural elements typically represent the largest portion of upfront embodied carbon, so keeping these components allowed the project to start with a substantial carbon saving compared with a completely new build.
The project achieved a 5.5-star NABERS target rating. Can you explain what operational strategies and design features would be necessary to achieve this rating?
During the feasibility stage, we ensured that the design approach and assessment methodology considered all aspects of operational performance. First, we adopted a whole-building approach, balancing factors such as fabric performance and glazing ratios. It was also important to ensure that, even within a refurbished building, there was adequate space and infrastructure to support the metering requirements needed for a NABERS UK ratable building. This foundation allowed us to optimise the building’s performance and refine the design elements required to achieve a strong operational energy rating.
A mixed-mode ventilation strategy was a key part of the optimisation exercise in early Stage 2. We explored how opening and closing windows could reduce heating and cooling demand and energy consumption. By analysing low- and high-level openings in specific locations across the façade, we identified the potential to reduce cooling demand by around 50%. Since NABERS UK Base Build ratings are based on energy consumption, reducing cooling demand had a significant impact on the rating outcome.
When we progressed to the formal Design for Performance assessment, the modelling confirmed the earlier analysis, demonstrating that the predicted 50% reduction in cooling demand was achievable under the selected design scenario.
From our baseline assessment, we concluded that achieving a 5.5-star rating was feasible for B100. The mixed-mode strategy also created a valuable performance buffer, if operational changes occur during the building lifecycle, there is still a margin to maintain a high NABERS rating.
Demand-led ventilation also played an important role in optimising heating and cooling loads. This allowed the mechanical systems to be sized more efficiently, enabling the use of highly efficient VRF systems as part of the overall design approach.
How would you balance achieving a high NABERS target rating (5.5 stars) while also targeting BREEAM Excellent on the same project?
Throughout the project, there was very little conflict between the two frameworks. In fact, we found that NABERS UK complements BREEAM very well. For the B100 project, BREEAM was initially selected as the primary sustainability benchmarking tool. NABERS UK was considered alongside this during the Stage 2 and 3 design optimisation.
As the project developed, we worked with the client to demonstrate the value of targeting NABERS UK alongside BREEAM. By designing a building that performs well operationally, you can achieve strong energy credits within BREEAM while also supporting the NABERS UK performance-based assessment. Once this relationship was clearly demonstrated, pursuing both BREEAM Excellent and a NABERS UK 5.5 star rating became a natural and efficient process.
The building uses a mixed-mode ventilation strategy with openable windows. How does this contribute to NABERS performance, and what challenges might this present?
Once the mixed-mode strategy was established, the next challenge was determining how it would operate in practice. We considered automated window systems with actuators, which would allow windows to open and close automatically. However, the additional installation costs and long-term maintenance requirements made this option less attractive.
Instead, we chose a more practical solution focused on tenant engagement. An alert system was designed to notify occupants when external conditions were suitable for opening or closing windows. This approach encouraged tenants to take an active role in the building’s environmental performance. While this introduces some uncertainty, since tenant behaviour cannot always be guaranteed, we aimed to make the process as simple as possible. The building management system predicts “open-window” or “closed-window” days based on weather forecasts. Occupants are then notified when windows should be opened and later closed. Magnetic sensors were also installed in the windows so that when they are opened, the HVAC systems automatically switch off, preventing energy waste.
Ultimately, the success of this strategy relies on achieving the right balance between tenant engagement, comfort, and HVAC performance.
How would you verify NABERS operational energy performance during the 12-month assessment period post-completion?
A soft-landing approach is essential before the formal 12-month assessment period begins.
In the year leading up to the official NABERS assessment, it is possible to carry out monthly or periodic performance checks to ensure the building systems are operating as intended and are aligned with the target performance.
Seasonal commissioning is also critical to ensure systems perform correctly across different conditions. Establishing a strong operational foundation allows the building’s performance to be tracked and benchmarked against the original design models.
If deviations occur, the model can be revisited and adjustments are made. This preparation period significantly reduces the risk of underperformance during the formal NABERS assessment. Savills’ Building Simulation Team offers this type of support as a de-risking service during projects.
The client wanted to "future-proof" the asset and achieve HQ-level rents. How do you translate NABERS ratings and sustainability features into commercial value for landlords?
Linking sustainability performance with commercial value is an ongoing conversation in the industry. While demonstrating a direct link between higher rents and sustainability credentials such as a NABERS rating, can be complex. There is increasing evidence of “green premiums” associated with high-performing buildings.
For retrofit projects, value is not created solely through energy performance. Factors such as building aesthetics, occupant comfort, and overall user experience also play a role. However, strong sustainability credentials can support higher rental values by reducing operational costs and utility bills for tenants. This also helps occupiers meet their own carbon reduction targets.
There has also been growing debate around the limitations of EPCs as a measure of building performance. Many stakeholders are recognising that EPCs alone do not provide a complete picture of operational performance. This is where NABERS UK provides significant value, as it measures actual, in-use performance rather than theoretical design performance.
NABERS UK is increasingly recognised as a valuable tool for improving operational performance in the office sector. With buildings representing a significant proportion of global carbon emissions, performance-based frameworks such as NABERS UK play an important role in driving real change.
As the industry moves toward more robust performance standards, schemes like NABERS UK will continue to support the delivery of high-performing, future-proofed buildings. Learn more about NABERS UK and how verified operational energy ratings can support your building performance journey, visit the NABERS UK.