UK NZCBS releases key reports detailing limit setting methodology and updated guidance, underpinned by Verco-created data model
May 2025 marked a significant release from the UK Net Zero Carbon Buildings Standard (UK NZCBS), providing crucial insight into the methodology behind its performance limits and an updated version of the Standard itself. This suite of documents aims to solidify a science-led approach to decarbonising the UK's built environment, aligning with national carbon targets.
A central publication is the report titled How the UKNZCBS Limits Were Set: Balancing the UK stock against a Net Zero trajectory to derive the Pilot Version limits. This document explains the background modelling used to inform the operational energy and upfront carbon limits in the Pilot Version of the Standard. The fundamental principle guiding this process is that the Standard is science-led, informed by the UK's carbon and energy budgets required to remain within a 1.5°C global heating trajectory. To achieve this, modelling was conducted on the UK building stock's evolution through to 2050, considering associated energy use and carbon impacts.
Key to this complex modelling effort is a sophisticated Excel-based balancing tool. Verco, supported by Turley, were appointed to create the functional data model which brought the vast amount of information together in one place.
Capabilities of the balancing tool
The tool enables the crucial balancing of "Bottom Up" energy and carbon expenditure from individual assets with "Top Down" energy and carbon budgets required at the stock level.
Julie Godefroy (CIBSE) and Clara Bagenal George (LETI) – as members of the TSG on behalf of the UK NZCBS – worked together with Verco over many months to establish and develop the model. The Tool was then tested and refined by Julie and Clara to create the performance scenarios that are fundamental to the Standard's limit setting process.
The "Bottom Up" element, managed within this tool, represents the performance achievable at the asset level, informed by data from projects, industry benchmarks, expertise, and comparisons with other schemes like Passivhaus and NABERS.
This balancing exercise directly informed the development of the UK NZCBS Pilot limits.
- For New Build projects, the limits represent best practice, described as feasible yet ambitious, with the goal of minimising future retrofit needs and limiting embodied carbon spend early on.
For the Existing Stock, the limits reflect what is anticipated from the majority of buildings, representing a "medium" depth retrofit intervention, which involves improvements like fabric upgrades and switching to electric heating.
While ambitious, these existing stock limits are noted as being less stringent than some current best-practice retrofits like Enerphit or LETI Climate Emergency Retrofit Best Practice.
Accompanying reports and revisions
Accompanying this foundational report is The UKNZBCS Input Evidence Report. This document complements the summary in "How the UK NZCBS Limits Were Set" by providing more detailed information on how the performance levels and the UK NZCBS limits were specifically developed, leveraging the data consolidated within the model created by Verco. It consolidates the analysis of industry data and expert feedback that informed the limit-setting process.
In addition to these reports, the UK NZCBS has also published Pilot Version rev2 of the Standard. This version incorporates minor amendments to the initial Pilot Version, with key updates documented within Section 4.1.2 (Table 2) of the Standard. The Standard itself is a comprehensive document covering various aspects of net zero carbon assessment, including scope, principles, assessment methodologies, metrics, limits, and submission requirements. It includes annexes detailing limits and targets (Annex A) and a submission proforma (Annex B).
These new publications provide essential transparency and technical detail on the UK NZCBS framework, equipping the industry with the knowledge needed to design, construct, and operate buildings in line with the UK's net zero carbon objectives.
Verco continues to support the Pilot Phase
Verco is currently providing support to a number of our clients throughout the NZCBS Pilot Phase. We are pleased to be informing the continued development of the Standard and supporting our clients in both interpreting the technical requirements and the application of these across their portfolios.
If you are interested in how Verco can help you assess your buildings or prepare for the standard’s launch later this year, please contact Rayan Azhari.
