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CIBSE guidance to deliver net zero carbon new buildings and how it relates to LETI

CIBSE has been actively working on climate change mitigation and adaptation and the links to building performance for two decades. Nearly every new building constructed in the UK from now on will be part of the existing stock in 2050. CIBSE therefore proposes that all new buildings should be net zero operational carbon from 2030 and moving to a regulatory regime based on operational energy performance.

Overall position on route to operational net zero carbon for new buildings

The London Energy Transformation Initiative (LETI) is a network of over 1000 built environment professionals working together to map the path to a zero carbon future. CIBSE has been involved with LETI from its initial stages. Following a wide ranging industry consultation LETI has prepared a one-page summary on the key features of Net Zero Operational Carbon buildings. The development of the one-pager was supported by the UK-GBC, Better Buildings Partnership, Good Homes Alliance, RIBA, and CIBSE.

CIBSE supports the proposed direction towards operational net zero carbon buildings, in particular:

  • Settings targets in energy use, which reflect the building’s performance independently from the grid
  • Supplying that demand from low-carbon energy sources
  • Only relying on off-site solutions as the last step, if needed, for additional carbon reductions
  • Monitoring and disclosing performance in use.

For more detail on CIBSE recommendations towards net zero carbon buildings, see:

See also CIBSE’s Climate Action Plan and the associated webinar for information on our overall activities towards net zero carbon; these cover policy and guidance, as summarised here, but also wider activities including research, education, and professional development.

Important note: This page focuses on new buildings. While much of the technical information is relevant to existing buildings and retrofit projects too, some aspects (e.g. heating systems, energy targets) will necessarily be different or more challenging in existing buildings and retrofits.

Do get in touch ( ) if you would like to find out more, have comments, or would like to be involved with any workstream to continually update and develop CIBSE guidance on net zero carbon, for new and existing buildings and for retrofit projects.

CIBSE policies and guidance which support Net Zero Carbon and the implementation of the LETI one-pager

View/Download LETI one-pager as a PDF

Select the circles for a brief summary of CIBSE's position on each area or go to the boxes below for details of CIBSE positions and relevant guidance.


Full details of the key relevant policy positions and guidance from CIBSE relating to the headings in the one pager above can be found below. This page is updated as our guidance develops, so please check it regularly.  Much of CIBSE guidance is dedicated to designing, operating and maintaining energy efficient and low-carbon buildings. It is therefore not possible to list all relevant guidance here.


CIBSE supports the approach of setting targets for energy use during the operation of a building, alongside any carbon targets, in order to reflect the energy performance of the building independently from the carbon content of the energy systems which supply the building. This could be in Energy Use Intensity (EUI-kWh/m2/yr), or as targets which take some account of contextual factors, such as DEC ratings, or base building ratings (as per Note 2 in the LETI one-pager).

Specific targets may evolve as practice develops and as more data is gathered and shared, hence the importance of measurement and verification.  

For an illustration of how industry targets (e.g. LETI, RIBA 2030 Challenge) relate to CIBSE energy benchmarks in offices, see this webinar (slide 30).

Additional information useful at the design stage is found throughout CIBSE guidance e.g.:

- CIBSE TM60, for measures in the housing sector
- CIBSE AM11 and TM54 on modelling and energy prediction - CIBSE TM54 is currently being revised.
- CIBSE Guide H on controls – planned revision

CIBSE supports demand reduction and management measures. We have set up a new working group on electrical engineering towards net zero carbon, working on guidance on topics such as peak demand reduction, demand management (including storage), integration of buildings and vehicles, interactions with the energy system, and more generally to support the electrification of buildings. Get in touch with our Technical Manager Julie Godefroy at for more information or to get involved.


CIBSE supports the approach of minimising the use of fossil fuels and maximising on-site renewable energy generation.

Policy positions:

Heat Strategy: CIBSE response to 2018 heat framework consultation.
Heat Networks: CIBSE response to 2021 consultation on Green Heat Networks Fund

Existing guidance on low-carbon systems:

- Heat pumps: Guide B1 1.7.9, TM51 ground source heat pumps (revision being planned), CP2 surface-water heat pumps, and CP3 open-loop groundwater heat pumps. See also Upcoming Guidance below.

- Biomass: Guide B1 1.7.6, AM15 - note that biomass installations are not recommended where air quality is a concern e.g. urban areas and Air Quality Management Areas. In the long-term they are also not in line with the recommendations of the Committee on Climate Change, which would prioritise the use of biomass for large-scale centralised installations with carbon capture and storage.

- Solar thermal: Guide B1 1.7.11, HVSH Solar heating design and installation guide

- PVs and solar thermal: KS15 Capturing solar energy.

Upcoming guidance on low-carbon systems:

- Hot water temperatures: upcoming guidance being drafted: in 2019 we set up a working group on guidance to facilitate energy savings and the integration of low-carbon sources, while ensuring health and safety (including addressing legionella risk); in the meantime, guidance on minimising the risk of legionnaires disease is provided in TM13, and more information on the working group’s early lines of thoughts can be found in this CIBSE Journal article (January 2020).

- Individual domestic heat pumps: Domestic Building Services Panel Domestic Heating Guide, revision being drafted.

- Heat pumps in multi-residential schemes: new upcoming CIBSE publication, currently being drafted. 

Heat networks: CIBSE acknowledges that there are situations where schemes may be required to connect to an existing heat network which still relies on fossil fuels (e.g. for planning requirements), or where a heat network may open opportunities for decarbonisation of a surrounding area (e.g. in historic districts where the scope for building interventions is more limited). This should be thoroughly assessed on a case by case basis, to avoid continued long-term reliance on fossil fuels.

The assessment should include a comparison with other options, based on expected carbon performance on a like-for-like basis (not relying, for example, on arbitrary factors which artificially support some options, such as used in Part L calculations).  Connection to the network should also be on the condition of a clear and reliable plan for the network to transition to fossil fuel-free sources in the future. See also our policy response which sets out our position on how new and existing heat networks should be assessed:

Electrification of heat: CIBSE has set up a new working group on electrical engineering for net zero, whose work will support heat decarbonisation – see “Low energy use” section above.

Hydrogen: CIBSE is contributing to strategic industry guidance on hydrogen. In addition, our Air Quality working group is preparing a briefing note on the air quality impacts of hydrogen combustion.


CIBSE has long advocated post-occupancy monitoring and disclosure of energy use. In-use performance data is required to apply for CIBSE awards. In 2019 we signed the cross-industry Building Performance Network statement asking for regulations and disclosure of in-use performance. CIBSE members can support this by signing the statement and/or monitoring and disclosing the performance of their offices.

The submission of post-occupancy data is a requirement for the CIBSE awards.

CIBSE publishes online energy benchmarks based on in-use data. Future phases will allow more frequent revisions and include more features e.g. new categories, visualisation of projects or portfolios against overall distribution. For more information and to contribute data, get in touch with our Head of Research Anastasia Mylona at

For an illustration of how industry targets (e.g. LETI, RIBA 2030 Challenge) relate to CIBSE energy benchmarks in offices, see this webinar (slide 30).

Additional information on how to assess, fine-tune and improve performance is found throughout CIBSE guidance e.g.

CIBSE Commissioning Codes
CIBSE Guide M on maintenance engineering & management
TM61 Operational Performance of Buildings, 2020
TM62: Operational performance: Surveying occupant satisfaction, 2020
TM63: Operational performance: Building performance modelling and calibration for evaluation of energy in-use, 2020
TM64: Operational performance: Indoor air quality - emissions sources and mitigation measures, 2020
TM39: Building Energy Metering - in revision.


CIBSE supports attention to reducing embodied carbon impacts from building services. There are many opportunities for strategies that reduce both operational and embodied carbon, particularly when reducing peak and annual demand, and associated plant requirements.

CIBSE TM56 Resource Efficiency of Building Services, 2014
CIBSE TM65, Embodied Carbon in building services: a calculation methodology, 2021

CIBSE recommends their members request Environmental Product Declarations (EPDs) for key items of plant when liaising with potential suppliers and manufacturers, in order to support the development of more widespread EPDs and more robust and consistent comparisons of embodied impacts. Where EPDs are not available, CIBSE TM65 sets out a recommended approach depending on the level of information available. We encourage the calculations done according to TM65 to be sent to CIBSE, as we will be collating it and creating a database for use by all. The forms associated with TM65 can be accessed here.

Upcoming guidance:

CIBSE is supporting research projects on embodied carbon, and further guidance is expected in the near future as a result.


CIBSE supports the approach that reliance on off-site carbon reductions should be minimised, and reductions should be demonstrated to be truly additional.  

A building should not be considered net zero carbon by relying on a “green electricity” (renewable) tariff.