Module 201: Seeking net zero in the built environment

This module considers recent and forthcoming guidance aimed at helping the UK to achieve net zero in the built environment

The recent, unprecedented, high outdoor temperatures and widespread flooding around the world have provided a stark reminder that climate change and global heating is not pausing as the world looks towards a 2050 deadline for carbon neutrality. The built environment in the UK and around the world is increasingly committing to achieve net zero buildings.

This CPD will consider recent and forthcoming guidance from a collection of concerned professionals and institutions in the UK that is aimed at improving understanding of metrics, methods and validation, in order to move from good intentions towards realistic, effective action.

Most countries and many corporations are already grappling with mitigation measures, and seeking long-term solutions to avert the climate crisis, while also maintaining a handle on pandemic control.1

The built environment is responsible for much of the world’s energy use and carbon emissions, and many nations – including those of the UK – have set what appear to be challenging targets on the path to limit climate change.

However, it may be that the route is paved with good intentions, misunderstanding or, potentially, meaningful obfuscations, and the recent Intergovernmental Panel on Climate Change (IPCC) working group 3 report Mitigation of Climate Change2 did little to inspire confidence in progress so far.

To keep global warming to no more than 1.5K – as called for in the Paris Agreement3 – emissions need to be reduced by 45% by 2030 and reach net zero by 2050.4 The UN puts it simply: ‘Net zero means cutting greenhouse gas (GHG) emissions to as close to zero as possible, with any remaining emissions re-absorbed from the atmosphere, by oceans and forests, for instance.’5

The provision of energy – including electricity – transport, manufacturing, buildings, fugitive emissions and other fossil fuels is most significant, accounting for 75% of global emissions in 2018.6 The building and construction sector, an inveterate user of energy, accounted for 36% of global final energy consumption and 37% of energy-related CO2 emissions in 2020.7

Although the UN encapsulates the task ahead in those few words, a quick Google search will uncover hundreds, if not thousands, of interpretations of how this translates in terms of the built environment, and what is needed to move towards a net zero existence for our buildings in a timely manner.

The publication of five short briefing documents8 by LETI (see panel, ‘LETI’), in conjunction with the UK Green Building Council, Better Buildings Partnership, Good Homes Alliance, the Royal Institute of British Architects and CIBSE, sets out the foundation of contemporary UK knowledge and thinking.

The documents described in the boxout provide a base on which to develop a better understanding of the issues and mechanisms involved in the development of net zero built environments.

The reformational proposals in these documents – and the ensuing industry consultation, reviews and questions raised on the facts, assertions, developments and interpretations – have stimulated the publication of answers to a set of 27 frequently asked questions (FAQs).

These have been evolved from a survey undertaken by CIBSE and LETI in late 2021, specifically 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). 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 forestry-based 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 carbon emissions from energy use, as, ultimately, all buildings will need all energy use to be met by zero carbon sources. Offsets are only for unavoidable emissions, particularly in a transition period while all parts of the economy decarbonise.

This may be to offset embodied carbon emissions, while still meeting local upfront and embodied carbon targets; (selected) upstream emissions from energy generation and distribution; and GHG emissions arising from water supply and wastewater treatment, while still meeting local water-use targets. Upstream emissions are extensively explained in FAQ 21, where they are referred to as ‘well-to-tank’ emissions from the production, processing and delivery of a fuel.

This applies to: biomass, such as in the processing and transport of pellets; natural gas, including extraction and processing; and electricity if, for example, it is generated using biomass, oil or gas. Several worked examples are included.

It may seem anomalous that building-mounted solar photovoltaic (PV) panels are excluded from the LETI embodied carbon targets. The notes on FAQ 25 explain that the rationale is that PVs are part of the wider energy system, helping to decarbonise electricity.

The embodied carbon of that wider infrastructure is not included in buildings’ embodied carbon targets, so including PVs would not provide a ‘fair’ comparison and could disincentivise their installation.

The commentary accepts that the boundary is not always clear – for example, when PVs are integrated as a façade element, as these elements are included in embodied carbon targets.

Solar thermal systems are included in the calculations for embodied carbon targets, as these systems only connect to the building, not to a wider network/infrastructure.

Figure 1: Example of recently developed external unit for variable refrigerant for (VRF) system, operating with a R-32 twin-rotary compressor with liquid injection, split heat exchanger, sub-cooling plate heat exchanger, a high-performance fan motor, and novel control features, all contributing to providing a SEER up to 8.9 and SCOP up to 4.67

The increasing cachet of delivering a more environmentally responsible built environment undoubtedly contributed to the inclusion of FAQ 15, which asks whether achievements towards delivering operational energy aspects of net zero carbon can be acknowledged at the various stages of project delivery.

It is noted that net zero in progress (NZiP) status can be claimed at different project stages – such as for a building that is being designed, or has been completed – to meet energy use targets that can be evidenced with design-stage predictive energy modelling calculations.

Manufacturers of environmental plant are responding to the demand to reduce operational impact with product developments such as the example illustrated in Figure 1. A building could then be handed over to the occupier to follow on with compliant operation to meet net zero.

The response to FAQ 16 adds that the designation of NZiP can also apply to existing buildings that do not burn fossil fuels and have a net zero retrofit plan in place to meet the energy targets with on- or offsite renewable energy for all energy use, with any offsets clearly established for upstream emissions.

These FAQs add significantly to existing resources from CIBSE and LETI, such as the 2020 LETI Climate emergency design guide and 2021 CIBSE TM65 Embodied carbon in building services: A calculation methodology. The authors conclude that work is needed, and is being planned, in collaboration with other industry bodies to develop further clarity and consensus on net zero.

There is, undoubtedly, scope for further directed guidance and action to deliver changes in the way that buildings are constructed and used to reduce environmental impact. In recent months, a group of UK organisations and professional institutions, including CIBSE, have come together to form a technical steering10 group with the aim of developing the ‘UK Net Zero Carbon Buildings Standard’.

This group will establish task groups of technical and sector-specific experts to determine realistic sector-specific embodied and operational benchmarks for what is currently possible and for what is likely to be possible in the future.

This will be founded on robust carbon-accounting methodologies, assessed and agreed as part of this project, and will include proposals of the requirements for credible validation.

A recent UK court case indicates11 that government is still seeking the detail of how the current net zero policies will reach targets, making it all the more important that the industry swiftly develops clarity of purpose and – more importantly – practical metrics, applications and solutions. The work discussed in this article is but a step on the critical path towards net zero.


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 to produce 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 building’s 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

© Tim Dwyer, 2022.