The UK Net Zero Carbon Buildings Standard (UKNZCBS) has been developed by a technical steering group of UK professional bodies and organisations, including RICS.
Two years of close collaboration with the group saw input from more than 350 experts involved in several working groups, with feedback from the broader industry through consultations and engagement events.
Developing on previous collaborative initiatives such as the Net zero carbon buildings: A framework definition and the Net zero whole life carbon roadmap, the UKNZCBS provides a technical definition for net-zero carbon buildings in the UK context, aligns these with national climate commitments and takes into account future decarbonisation of energy supply, as well as new and existing buildings' performance.
Pilot version sets carbon thresholds
Performance levels are based on a large body of evidence collected in 2023, covering emissions embodied in manufacturing and construction – known as upfront carbon – as well as those generated by energy consumption during building operations.
Published in September, the pilot version of the UKNZCBS contains the metrics that must be assessed and the thresholds to be met for a building to conform with the standard. The methodology for measuring energy and carbon is based on RICS' Whole life carbon assessment for the built environment.
Maximum limits are set both on upfront carbon from construction and annual energy consumption. There is also a minimum target for renewable energy generation, while no on-site fossil fuel consumption – via, for example, gas boilers – is allowed.
Thresholds such as these are set differently for new and existing buildings, and also vary depending on building type – for example, the limit for energy use in offices in 2025 is set at 85kWh/m2 per year, while for flats it is 40kWh/m2 per year.
There are also several metrics that are required to be assessed and disclosed when applying for verification against the standard. It is expected that professionals with relevant expertise will be tasked to perform such assessments on behalf of building owners who wish to claim conformity with the standard.
Meeting all these requirements means that an owner can legitimately claim their building is 'net-zero aligned' as defined in the UKNZBCS – which means its performance is consistent with the UK target to be net-zero carbon by 2050.
There is an option to procure carbon credits and green energy to offset any emissions remaining once thresholds have been achieved, but this does not affect the limits and targets that must be met in the first place.
Offsetting cannot therefore be used as a short cut to net zero while avoiding actual emission reductions at the building level.
Verification based on measurement not modelling
Any claim of conformity with the UKNZCBS will need to be verified by a qualified third-party expert, so it will not be possible to self-certify net-zero alignment. The verification process will be developed during 2025. At the same time, a pilot scheme will be used to assess the application of the standard to real projects and engage with developers, designers, and building owners.
Lessons learned from the pilot will be used to inform the first complete version of the UKNZCBS. This will be published towards the end of 2025, and will also include details of the verification process.
Crucially, the UKNZCBS is designed to demonstrate alignment through measured rather than predicted performance. Therefore, embodied carbon must be assessed after completion by using measured quantities rather than design estimates, while operational energy and carbon are assessed annually from meter readings of actual consumption rather than modelling.
This means that each claim of net-zero alignment is linked to a specific year, and is renewed every following year with reporting and verification. Conformity with the UKNZCBS cannot be claimed before the building is used at full capacity, which means that buildings at design and construction stages, or even those that have been completed but are not fully occupied yet, cannot claim to be net-zero aligned.
'Each claim of net-zero alignment is linked to a specific year, and renewed every following year with reporting and verification'
Approach addresses performance gap and greenwashing
The focus on actual performance as-built and in-use has been designed to address the so-called performance gap; that is, the difference between a performance forecast from energy modelling at design stage and the actual performance of the building as measured in meter readings.
Along with the requirement for third-party verification, in practical terms this eliminates the chances of using the UKNZCBS for greenwashing.
However, the fact that claims can only be verified after the building is occupied does not mean that the UKNZCBS cannot be used at planning and design stages as a meaningful target. For example, new buildings will need to be specifically designed – and built – to be capable of performing within the limits of the UKNZCBS once they are occupied.
Moreover, the exclusive focus on in-use performance clearly distinguishes the UKNZCBS from schemes such as BREEAM, or Low Carbon Building Initiative, where green certification can also be achieved at the design stage.
National commitments applied at asset level
Although it takes a similar approach to the Science Based Targets initiative, the UKNZCBS differs by applying to individual assets rather than at company level.
The decarbonisation scenario that underpins the UKNZCBS allocates the carbon budget of UK building stock to different types and construction works on the basis of a fair distribution and what is achievable in reality.
Fairness is established by the Technical Steering Group, and involves distributing evenly the carbon budgets across building sectors by, for example, not setting limits that are too hard for homes to achieve or too easy for retail to achieve.
As such, it can be considered the most complex and detailed study to be conducted so far in Europe that is designed to translate national-level climate commitments, such as the Paris Agreement, into asset-specific performance levels.
Through its revised Energy Performance of Buildings Directive, the European Union has shown its intent to mandate member states to conduct similar analysis and use the results to update their respective building regulations.
Market can continue to engage in development
The UK construction and real-estate sectors can be proud to have led this crucial move towards building decarbonisation.
Overall, the UKNZCBS sends a clear message to the market: there can be no more doubts about the performance levels required for net zero, and the robustness of any claim can now be judged against a comprehensive set of verifiable criteria developed by the industry itself.
The high levels of engagement during development and after the pilot publication – with, for example, over 2,000 people joining the launch webinar in October – shows the wide support for the standard.
Individuals and companies working in construction and real estate can expect to come across the standard in different ways, according to their respective professions. For example, building surveyors may be asked by clients to assess properties' ability to meet the UKNZCBS, and collect the evidence required to demonstrate conformity. Facilities managers could meanwhile be required to ensure energy consumption meets the annual limit.
It is therefore important for professionals to understand the main features of the UKNZCBS and how it is applied. To help them do this, the pilot version is accompanied by introductory slides and a webinar that present the main aspects of the standard.