While climate change has become an increasingly prominent topic in global discourse, not all rhetoric supports meaningful progress. Some world leaders continue to downplay or delay decisive action, risking a loss of momentum. This hesitancy is, in part, fuelled by vocal climate sceptics who dispute the scientific consensus on anthropogenic climate change –many of whose arguments are effectively countered at resources such as SkepticalScience.com.1
The UK experienced an unseasonably warm and dry start to April 2025 – welcome news for day-trippers perhaps, but a stark reminder of our changing climate. March 2025 marked the twentieth month in a 21-month run where global-average surface temperatures exceeded 1.5K above pre-industrial levels.2
As shown in Figure 1, warming seas are driving record-low sea ice at both poles, pushing global sea ice cover to an all-time minimum.3 The implications are severe: reduced albedo accelerates warming; melting sea ice disrupts jet streams and ocean currents; and there are direct impacts on ecosystems and communities.
By early April 2025, the UK had already seen 286 wildfires – 100 more than during the same period in 2022, itself a record-breaking year.4 Meanwhile, since mid-20235 northern hemisphere land temperatures have been consistently over 2K above 20th-century norms, highlighting increasing pressure on people and built environments.
Globally, the effects are stark. Delhi reached 41°C in April 2025 (compared with a historical average of 37°C), and in 2024, Rajasthan saw 50.5°C, leading to 40,000 suspected heatstroke cases and at least 150 deaths.6 Such extreme weather events – floods, wildfires and heatwaves – are becoming alarmingly common across all continents.
In response, the global push for net zero carbon buildings continues to gain traction. While approaches differ by region, there is growing alignment on the need to address both operational and embodied carbon.
Net zero frameworks typically consider emissions generated during a building’s operation –such as energy use for heating, cooling and lighting – as well as the embodied carbon resulting from construction materials and processes. Energy efficiency lies at the heart of these standards. Strategies include optimising insulation, deploying high-performance heating, ventilation and air conditioning (HVAC) systems, and integrating renewable energy sources either onsite or via offsite supply.
The aim is to minimise energy demand while ensuring that remaining consumption is met through clean, sustainable means. Typically, such standards and guidelines target increasing regulatory and policy pressure to achieve building decarbonisation across life-cycles. There are many actions and initiatives around the world aimed at net zero built environments – some of the key ones are shown in Table 1.
Table 1: An example of regional and national net zero building initiatives
Australia:
- Advancement of net zero-ready buildings through initiatives led by the Green Building Council of Australia (GBCA).
- Integration of Nabers ratings and other performance-based schemes.
Canada:
- Implementation of the Canada Green Building Council’s Zero Carbon Building Standard.
- Adoption by both new construction and deep retrofit projects.
China:
- Expansion of the Green Building Evaluation Standard (GBES) for national compliance.
- Acceleration of ultra-low energy and net zero energy pilot projects.
- Integration of renewable energy within urban planning and building design.
- Inclusion of net zero principles in smart city frameworks.
European Union (EU):
- Enforcement of the revised Energy Performance of Buildings Directive (EPBD).
- Mandated transition to Zero-Emission Buildings (ZEBs) by 2030 (2028 for public sector buildings).
- Emphasis on Whole Life-Cycle (WLC) carbon assessment and reporting.
- Fossil fuel boiler phase-out target set for 2040.
- Renovation Wave strategy focused on improving the energy performance of the existing building stock.
- Strengthening of Energy Performance Certificates (EPCs) to increase reliability and comparability.
India:
- Deployment of the Energy Conservation Building Code (ECBC) for commercial buildings, with progressive efficiency tiers.
- Emphasis on passive design strategies and renewable energy integration.
- Varied implementation at the state level, with incentives in certain regions.
Middle East (UAE, Saudi Arabia, Qatar, Oman):
- Introduction of national energy strategies and efficiency regulations (for example, ECAS, SEEP).
- Localised green building certification systems such as GSAS and Estidama.
- Focus on high-performance buildings in new urban developments.
United States (US):
- LEED Zero certification supporting net zero targets across carbon, energy, water, and waste.
- Proliferation of state- and city-level building energy codes with net zero ambitions (for example, California Title 24).
- Engagement with the World Green Building Council’s Net Zero Carbon Buildings Commitment.
The transition to a net zero carbon built environment has been accelerated in the UK with the launch in late 2024 of the pilot version of the UK Net Zero Carbon Buildings Standard7 (UK NZCBS). A significant factor in the credibility of the standard is that it has been developed collaboratively by a broad coalition of stakeholders8 from the built environment (including CIBSE).
The standard aims to bring cross-industry consistency and clarity to what it means for a building to be aligned with net zero carbon goals. The pilot version provides the foundation upon which future iterations will build, incorporating emerging data and best practice as the field evolves, and is applicable to building-related construction works and the operational use of buildings throughout the UK. It spans a wide range of sectors, including commercial residential; culture and entertainment; data centres; healthcare; higher education; homes; hotels; offices; retail; science and technology; sport and leisure; and storage and distribution.
The standard introduces ‘pass/fail metrics’, which are mandatory for assessment and may have associated numerical limits, and ‘reporting metrics’, which must be disclosed but do not yet have thresholds. At its core, the standard is underpinned by a suite of metrics, some of which determine compliance directly.
Buildings may be classified under a single sector or as mixed-use, based on the proportion of net internal area (NIA) – the usable area within a building – allocated to each sector. Tenanted buildings require more granular assessments.
Works undertaken in tenant areas below 500m² NIA may currently be excluded from full assessment, though this threshold is expected to reduce in future versions. Building owners are encouraged to adopt lease structures that mandate carbon data reporting from all tenants to ensure more robust and transparent evaluations.
The standard outlines specific requirements across several domains of building performance. Embodied carbon assessments must follow the ‘defined upfront carbon scope’ that refers to the inclusion of specific life-cycle stages as described in BS EN 159789 as modules A1 to A5 – shown in Table 2 – representing the carbon emitted before the building is operational. These are often emphasised because of the immediate nature of these emissions – they are irreversible once the building is constructed.
The UK NZCBS also helps project teams identify early design opportunities to reduce carbon – such as material selection, procurement routes, and construction methods. Products and materials outside the scope of the construction works are excluded.
While this version does not yet impose limits on whole-life embodied carbon, it sets upfront carbon limits (kgCO2e.m–² gross internal area (GIA)), which are to be treated as pass/fail metrics. Operational energy in terms of an energy use intensity (EUI) per m² GIA per year is a pass/fail metric, while operational carbon emissions intensity is a mandatory reporting metric. Sub-metering of additional use areas (AUAs) is encouraged for clarity and accuracy. Annual onsite renewable electricity generation per m² of building footprint is also a pass/fail metric. Importantly, exported electricity is excluded from energy use calculations.
Operational water use is reported both in absolute terms and normalised per m² GIA. While no current thresholds exist, future versions may introduce limits. The standard generally prohibits the use of fossil fuels but does outline specific exceptions.
All sectors, except for single-family homes and buildings under 500m² GIA, must undertake electricity demand management assessments. Future iterations of the standard are expected to introduce specific limits in this area as more data becomes available.
For buildings connected to district heating and cooling networks, the energy use and associated carbon impacts of heat and coolth must be assessed and reported. Rejected heat or cooling from other users – such as industrial processes – is deemed to have zero emissions.
The global warming potential of refrigerants is a pass/fail metric. Systems with a refrigerant carbon impact of 3,000kgCO2e or more must report associated leakage emissions.
While the standard prioritises in-built performance over offsetting, it includes guidance on acceptable offsetting methodologies for buildings seeking the ‘Net Zero Carbon Aligned Building (plus offsets)’ designation. (Carbon offsetting is usefully discussed in UK Parliament POSTnote 713.10)
Numerical limits and targets for each metric are provided (as an annex), segmented by building sector, project type (new build or retrofit), and project timeline. It includes upfront carbon limits, EUI thresholds, and sector-specific considerations.
Importantly, as a pilot version, the developers recognise that refinement will be necessary as new data and insights emerge. Future iterations are expected to include more stringent limits, expanded sector coverage and improved methodologies. Nonetheless, the standard maintains a pragmatic outlook, balancing ambition with the realities of industry capability. Examples of UK NZCBS metrics are given in Table 3. The ultimate goal is zero operational carbon through onsite renewables and/or credible offsets after having prioritised efficiency.
Delivered space heating and cooling (kWh.m–² per year, and peak W.m–² GIA)
- Using metered data where available.
Embodied carbon (kgCO₂e.m–² GIA)
- Covers modules A1–A5 at minimum (the ‘defined upfront carbon scope’) with no offsetting.
- Includes onsite renewable generating equipment (in terms of characteristic power).
Operational energy (kWh.m–² GIA per year)
- Principally relates to energy use intensity (EUI) for regulated and specific unregulated loads.
- Assessed using measured or modelled energy performance, depending on project stage.
Operational carbon emissions (kgCO₂e.m–² GIA per year)
- Based on the operational energy use, multiplied by UK carbon factors.
- Onsite derived renewable electricity assigned zero emission factor.
- CHP and district energy have relevant emission factors.
Minimum occupancy rate (% occupancy)
- Based on occupancy of occupiable spaces.
Water use (m3.m–² GIA per year)
- Several associated metrics including carbon emissions and person-related usage.
While reducing operational carbon – primarily from energy use – is essential, achieving net zero emissions in buildings requires a holistic approach that also accounts for embodied carbon. Mechanical, electrical and plumbing (MEP) manufacturers are increasingly recognising the importance of transparency and accuracy in embodied carbon assessments.
This data can be supplied through an Environmental Product Declaration (EPD), assessed in accordance with standards such as BS EN 15804:2012+A2:2019, BS ISO 14025, and BS ISO 21930. However, where an EPD is not available, embodied carbon can be estimated using the relatively straightforward methodology set out in CIBSE’s 2021 publication TM65: Embodied Carbon in Building Services.
TM65 provides a structured approach for estimating the embodied carbon of MEP systems (including lighting) in the absence of manufacturer-declared EPDs. It fills a crucial gap by offering a consistent methodology based on material data, industry averages, and published carbon factors. This enables manufacturers and design teams to generate embodied carbon estimates for MEP components, supporting more informed decisions in design, procurement, and sustainability assessments.
The TM65 methodology combines material weights with associated carbon factors and includes emissions from transport (based on typical distances), installation, and end-of-life scenarios to produce a product-level embodied carbon estimate. Where detailed material data is lacking, TM65 applies default values based on industry data and case studies. While these assumptions reduce precision, they still provide a valuable approximation during early design stages.
Although not as accurate as a full EPD, TM65 remains a useful tool for benchmarking, comparing design options, and identifying carbon reduction opportunities in MEP systems.
For more on TM65 and its sector-specific variants, refer to CIBSE Journal CPD 243 (December 2024).
Unlike traditional building entities, MEP systems can consist of numerous components – such as ductwork, air handling units, motors, and control systems – each with varying lifespans, materials, and carbon footprints. It is important that any carbon assessment methods capture the diversity of forms and materials that constitute MEP systems.
The manufacturer’s process often requires starting from scratch, critically evaluating every component, material choice and production method to understand and minimise environmental impact. Key considerations include material sourcing, since selecting low-carbon, recycled or responsibly-sourced materials can significantly reduce embodied carbon; and manufacturing efficiency, which involves optimising production processes to lower energy consumption and waste.
Product durability and end-of-life strategy also play a crucial role, as designing for longevity, reuse or recyclability enhances circular economy potential and reduces long-term carbon impact.
Unlike structural components, which often remain in place for 50 years or more, MEP systems typically require replacement several times in a building’s life. Consequently, embodied carbon from these systems is recurring over the building’s life, and the replacements should be properly accounted for as part of a life-cycle carbon assessment. The boxout ‘A net-zero carbon ventilation unit’ provides a summary of how one manufacturer has employed embodied carbon assessments to ensure that they can market their product as effectively ‘net zero carbon’.
A net zero carbon ventilation unit
The manufacturer of the CIBSE Building Performance Awards Air Quality Product of 2023, a hybrid ventilation with heat recovery unit (as shown in Figure 2), developed its product so that it could be delivered to site with a credential of zero embodied carbon.
By employing holistic embodied carbon assessments, the use of appropriate materials was optimised through an iterative process including, where appropriate, prioritising readily recyclable materials even when such materials may have higher embodied carbon – for example, the use of aluminium as opposed to galvanised steel.
This included exploring the integration of materials such as recyclable expanded polypropylene and aluminium, together with adopting lean manufacturing techniques11 to minimise waste and promote closed-loop recycling of materials in the production cycle.
Having determined the estimate of embodied carbon associated with the ventilation unit (from an EPD assessment), the manufacturer was able to assess the carbon offset that would be required. In this case, it employed the carbon offset certification provided by Gold Standard,12 regarded as one of the most credible, science-aligned and ethically-rigorous carbon standards. Having arranged (and funded) the offsets, the manufacturer can bring the product to market as ‘net zero carbon’.
Manufacturers play a vital role by enhancing transparency through EPDs and by employing methodologies such as TM65 to assess and reduce the embodied carbon of their products. While standards such as the UK NZCBS are evolving, they represent a crucial step towards a holistic approach to building decarbonisation, acknowledging the need for ambitious yet pragmatic targets, and the ongoing refinement of metrics and methodologies.
© Tim Dwyer 2025.
References:
- bit.ly/CJMay25CPD1 – accessed early April 2025.
- bit.ly/CJMay25CPD2 – accessed early April 2025.
- bit.ly/CJMay25CPD3 – accessed early April 2025.
- bit.ly/CJMay25CPD4 – accessed early April 2025.
- bit.ly/CJMay25CPD5 – accessed early April 2025.
- bit.ly/CJMay25CPD6 – accessed early April 2025.
- bit.ly/CJMay25CPD7 – accessed early April 2025.
- bit.ly/CJMay25CPD8 – accessed early April 2025.
- BS EN 15978:2011 Sustainability of construction works – Assessment of environmental performance of buildings – Calculation method, BSI 2011.
- bit.ly/CJMay25CPD9 – accessed early April 2025.
- Bicheno, J and Holweg, M, The Lean Toolbox: A Sourcebook for Process Improvement, 6th ed. Picsie Books, 2023.
- bit.ly/CJMay25CPD10 – accessed early April 2025.