The importance of defining net zero

An agreed set of net zero definitions is essential if the construction and property industry is to design consistently high-performing buildings. Julie Godefroy says a new initiative will provide more clarity for members

Dr Julie Godfrey is head of sustainability at CIBSE

Having a set of agreed, clear and comprehensive definitions for net zero buildings is necessary for investment, specifications, trusted and consistent reporting, certification and, ultimately, regulations.

There has been great progress on net zero definitions. The UK Green Building Council (UKGBC) framework1 was followed by the LETI one-pager on operational carbon2 (energy use), which is supported by CIBSE. Last year, the first version of the Whole Life Carbon Network (WLCN)-LETI3 set of definitions was published, which are supported by RIBA.

Over the past few months, CIBSE and LETI have been working together and engaging with industry. CIBSE wanted to interact with members before deciding whether to adopt the WLCN-LETI definitions. This was tested in a survey, and adoption was supported by 78% of members. The survey showed strong support for key principles in the FAQs (see panel below).

Interestingly, the survey also showed that, while clarity is needed now, there is an understanding that the definitions and FAQs may evolve – in particular, to include demand-management considerations.

These FAQs are not final, and CIBSE and LETI are continuing to work together

The survey tested opinions on how to acknowledge efforts towards net zero when a building faces constraints and limited agency. Responses were rather split, with many highlighting the risks of greenwash and confusion. Overall, there is broad consensus that only genuine constraints should be acknowledged.

The FAQs, therefore, propose to acknowledge ‘net zero in progress’ in two situations: buildings not able to meet the energy use and/or fossil-fuel criteria because of a forced connection to a heat network, if that network has a decarbonisation plan; and existing buildings not meeting the energy use targets, but with a retrofit plan in place.

The WLCN-LETI definitions provide principles, but it is difficult to cover, in a succinct and clear way, the range of situations a building and its energy supplies may face in practice. CIBSE has been working with LETI to produce a set of FAQs on the definitions, to support clients and project teams, and bring consistency to how definitions are applied.

Key principles

  1. The incorporation of energy use and embodied carbon targets in the net zero definitions, to promote efficient use of resources regardless of low carbon supplies
  2. No fossil-fuel combustion
  3. Renewable generation and procurement, prioritising on site generation. For offsite procurement, the FAQs refer to the UKGBC guidance on options such as power purchase agreements (PPAs) and green tariffs
  4. Offsets to be used only where necessary – in particular, to cover unavoidable embodied carbon emissions (once the targets are met) – and if robust. The FAQs refer to guidance from the UKGBC for criteria including additionality and verification, and encourages gradual reliance on ‘removal’ offsets (for example, trees) rather than just reducing emissions elsewhere

We produced a draft of the FAQs and asked for feedback in a survey in November, receiving around 200 responses across disciplines.

The 27 FAQs will be launched online on 7 April, and cover operational carbon from energy and water use, embodied carbon (upfront and life-cycle), offsets, net zero claims, and more detailed points, such as how to calculate ‘residual’, or upstream, emissions. They will be available from the LETI website and from the CIBSE Net Zero guidance page.

These FAQs are not final, and CIBSE and LETI are continuing to work together, and with others, to develop further guidance. Key areas of work are:

  • The approach to energy targets in buildings connected to district heating schemes
  • Energy-use targets in a broad range of sectors (beyond offices, schools and homes)
  • Embodied carbon targets (beyond offices, schools and homes), starting with upfront carbon
  • The evolution of the definitions in the future – for example, whether and how to further encourage onsite renewables and demand management

Contact Clara Bagenal George or Julie Godefroy to get involved. To watch the launch, register here.


1 Net Zero Carbon Buildings: A Framework Definition, UKGBC
2 Net Zero 1-Pager, LETI
3 Whole Life Carbon Network – LETI