CPD PROGRAMME | NET ZERO oriented towards the definitions, which sought to determine the level of agreement with the definitions and their interpretation, and attracted 198 responses. More than 75% of respondents self-identified as expert or having medium expertise, with the majority of responses from sustainability consultants, building services engineers and architects. The resulting FAQs still do not profess to provide the definitive answer to what net zero means, for all building types, but [provide] a step on the road and point towards a direction of approach. The FAQs and answers together with all the other documents referred to here are freely downloadable through the links given at the end of the article. As examples of the content, here are some of the notable discussions that have been drawn, in an edited form, from the answers to the FAQs. Example FAQs The fundamental FAQ 1 asks: Why does a building need to meet energy targets? The response notes that buildings cannot be considered in isolation and need to have low energy use to enable the most effective (financial/embodied carbon/ resources) development of a zero carbon Grid. It is contested that a building that is completely off-Grid should also be subject to energy targets, because that building will use embodied carbon resources for its onsite energy supplies and, by employing energy-efficient design, will maximise the opportunity to generate surplus energy, which could be used (exported) elsewhere. In terms of the type of energy target, the comments attached to FAQ 4 outlines that it should meet an energy use target such as an energy use intensity (EUI) or energy rating. Additionally, it recommends that appropriate heating/cooling design targets be set as a precursor to meeting those energy targets. As operational energy will play such a significant part in the lifetime impact, FAQ 10, Will the Net Zero Carbon Operational Energy definition be valid until 2050, or will it evolve?, is particularly important. The response notes that, although this is currently based on reducing annual energy use and employing energy from a renewable energy source, this may evolve to respond to a changing context such as meeting the needs of demand management to optimise, for example, peak demand and storage provision. The focus on annual energy use and renewable energy generation could also potentially evolve. Much of the success of a low carbon future is pinned on the decarbonising of the UK electricity Grid (and potentially the gas Grid). LETI Established in 2017, the London Energy Transformation Initiative (LETI) is now a UK network of more than 1,000 built environment professionals who are working together to put the UK on the path to a zero carbon future. The voluntary group is made up of developers, engineers, housing associations, architects, planners, academics, sustainability professionals, contractors and facilities managers. The group has been the catalyst for the production of several advisory documents, including the five summarised below, that, together, form a basis of current UK thinking on the definitions and processes employed in the development of net zero built environments. Net zero (one-pager) Published in 2019, as the widespread support for an acceleration to net zero carbon took hold. It provides: high-level benchmarks for total energy use intensity (EUI) for many building types; suggested frequency of validation audits for buildings; and the carbon auditing required to establish that a building achieves a net carbon balance. This provides a simple scene-setter for the subsequent short publications released in 2020 and 2021. Whole life carbon (Emissions) (one-pager) This describes how whole life carbon is the sum total of all building assets-related GHG emissions and removals, both operational and embodied, over the buildings life-cycle, including disposal. It provides a succinct commentary on methods applicable to asset life-cycle stages (as defined by BS EN 15978:20119), which includes phases (or modules): upfront product creation and construction; embodied carbon in-use and end-of-life stages; operation carbon in terms of energy and water; and, possibly the most difficult to quantify, circular economy, which incorporates reuse, recovery and recycling, and the potential future carbon benefit of a design decision made today. Embodied carbon (Emissions) (one-pager) Describing the GHG emissions and removals associated with materials and construction processes throughout the whole life-cycle of an asset. This is explained in terms of the BS EN 15978 life-cycle stages by: cradle to gate the product stages; cradle to practical completion; and cradle to grave, which includes all stages except the operational carbon. A hierarchical set of elemental reduction strategies provides suggestions for methods that may be employed to reduce embodied carbon. Embodied carbon target alignment This explains the need for consistent methods of measurement to produce standardised benchmarks, targets and performance metrics that are appropriate to the particular building types and applications. It explains that there is a need for embodied carbon reporting on all projects, requiring a rating system that may be contextually applied and accessible which, it suggests, should be based on a simple A-F scale. It includes examples of embodied carbon targets that have been developed for office, high-rise residential, education and retail sectors, noting the need for transparency in reporting to ensure validity. Carbon definitions for the built environment, buildings and infrastructure This aims to provide some consistency in basic definitions related to carbon and net zero carbon terminologies. This lexicon includes a useful base set of interpretations relating to definitions of carbon, infrastructure, net zero, and the terminology associated with offsetting, or compensating for, emissions. It includes a useful table that summarises tasks that would relate to achieving net zero carbon at each project stage. FAQ 9 asks if there is a point where renewable energy procurement will no longer be required, and the response is clear that all energy use should be met by on- or offsite renewable energy sources. Although the UK electricity Grid is continuing to decarbonise and is predicted as being net zero (or near) well before 2050, buildings must meet their needs through onsite or procured renewable energy generation (at the time of handover to the building operator). For a building that is supplied by green gas for example, created from anaerobic digestion the reply for FAQ 22 highlights that, if the anaerobic digestion happens on site, the green gas is deemed renewable and the building can qualify as net zero (if it meets the other requirements of the definition). The building must run 100% on green gas, or another renewable, so a net balance of exported green gas and imported natural gas is not acceptable. An important caveat is that, if it is employing forestrybased products for anaerobic digestion, they must be sustainably certified which effectively means they should be replaced. One of the most contentious areas in the reliability of net zero claims is the role that offsets play. The reply to FAQ 13 clarifies that offsets are not allowed to cover 90 September 2022 www.cibsejournal.com CIBSE Sept 22 pp89-92 CPD 201.indd 90 26/08/2022 14:57