Why hasn’t Part Z been mandated into Building Regulations yet?

The UK Green Building Council (UKGBC) estimates the UK releases around 64 million tonnes of embodied carbon (the emissions related to the production and use of materials) per year – more than aviation and shipping combined. As a result, this figure has remained static for around 30 years.

If it continues at this rate, the UKGBC forecasts the built environment will be responsible for the release of around 1,700 million tonnes of greenhouse gas emissions, during the period 2024-2050. Less than one-tenth of these emissions are tackled by existing regulation and the forthcoming Future Homes Standard and the Future Buildings Standard⁽¹⁾.

Despite this, continuous calls from key leaders and figures in the construction industry to regulate embodied carbon through whole life carbon assessments (WLCAs) are yet to come to fruition. The proposal to incorporate Part Z into existing building regulations was first introduced to parliament in February 2022, as part of the Carbon Emissions (Buildings) Bill. Later that year, the then Conservative government declined to support it. Forward wind to 2025 and a new Labour government just six months into its first term. Could the tide be turning in 2025? Will Arnold – Head of Climate Action at IStructE (The Institution of Structural Engineers) – has recently shared more than 200 statements of support from across the construction industry calling for embodied carbon regulation, with the relevant civil servants investigating the potential to regulate embodied carbon. Here, he shares his view and outlines why he believes sustainable practices and economic growth are inextricably linked.

Could mandated WLCAs hinder the government’s housebuilding progress?

Primarily, Arnold thinks government hesitation stems from concerns about meeting housebuilding targets. As he explains, there are concerns new regulations could make it harder to build houses, particularly smaller developments.

However, Arnold says: ‘Larger housebuilders are already addressing embodied carbon and would welcome consistent national regulations to streamline their processes saving time and money.’ He adds: ‘This is also true of developers and local authorities that are investing limited funds in creating local policy to fill the void left by national regulation. Part Z could be applied first to larger construction projects only, to avoid penalising smaller developers who haven’t yet upskilled.’

Among the supporters include household names such as Barratt Homes, NatWest, Morgan Sindall and British Land, down to SME design firms and housebuilders. Barratt Homes has said: ‘We welcome regulation to mandate the reporting of whole life carbon, leading to the eventual introduction of embodied carbon limits in construction’, while Waugh Thistleton Architects emphasises that: ‘Resource conscious decisions need to be at the forefront of design; such as whether to retain existing buildings. The sooner embodied carbon is regulated, the better.’

Interestingly, the EU has taken a progressive approach, mandating Member States to report embodied carbon by 2028 and to implement limits by 2030. In contrast, the UK remains an outlier, despite having industry-led initiatives like the Net Zero Carbon Buildings Standard and the Built Environment Carbon Database (BECD).

Instigate the demand signal

Arnold argues that in addition to supporting the government’s Net Zero targets, regulating WLCAs could also accelerate the economic growth the government claims to be wholly invested in.

He says: ‘The government strategy to build homes, meet its Net Zero laws, and achieve economic growth could all be achieved by regulating embodied carbon. There’s a desire in the materials sector to decarbonise but it currently lacks the boost that a clear demand signal would bring – for investors to invest, they need to know they’ll get a return on investment.’

He adds that mandated action could help to create a push in the market for low carbon materials. For example, laboratories have the tools and means to create zero carbon concrete, but they lack funding.

‘When practitioners have a process and methodology for measuring emissions, the next natural step is to reduce emissions. It’s at the forefront of their minds.’

Less carbon, less money

Arnold also thinks it’s possible for this to equate to saving money; one of the main criticisms levelled at mandating WLCAs is concern that it could increase project costs.

Arnold is keen to emphasise the exact opposite is often true. ‘Similar to a finance budget, a carbon budget – for example, 500kg per square metre – will encourage the team to address material efficiency, material reuse and low-carbon materials, from day one.’

These design decisions need to be made, ideally, from the outset of the project to avoid incurred costs later on – for example, the decision to design columns closer together would make a design more efficient, as Arnold explains. ‘It’s a bit like being at a gym class and asked to hold a “plank” position. If you’re allowed to rest your knees on the ground, you reduce the length that your body has to span, making the exercise easier. Similarly, move columns closer together, you make the job easier for your slabs and beams, which are the most material-hungry parts of most buildings.’ He points to other decisions such as smaller basements, or reduced complexity of construction, that can save cost and carbon together. Engineers play a fundamental role in offering guidance, regarding what will and won’t be feasible for existing buildings; especially for retrofitting schemes, in terms of adding additional storeys or impacting surrounding infrastructure.

He notes it would be straightforward to incorporate Part Z into existing building regulations, with the RICS whole life carbon assessment for the built environment standard as guidance; meaning no new bill or legislation would have to be put through Parliament.

Arnold highlights other measures that could help, such as addressing disparities in VAT – currently, developers have to pay VAT on materials for retrofit but not for new build.

Anticipating the future and the business case

Arnold observes many industry leaders are already preparing for future regulations. Their motivations fall into two main categories:

1. Business sense: Clients are increasingly demanding low-carbon solutions due to ESG requirements of their investors and funders, a trend expected to grow.
2. Personal responsibility: Professionals recognise the environmental impact of construction and want to contribute to meaningful change. For many, this is a deeply personal decision driven by a desire to create a sustainable future for the next generation.

The Net Zero Carbon Buildings Standard (NZCBS): A game changer

In the absence of a mandate, the NZCBS was developed with input from over 300 industry experts – including IStructE, the Carbon Trust, BRE, RIBA and UKGBC. The NZCBS provides a unified framework for demonstrating that a building is aligned with the UK’s Net Zero laws. The standard brings consistency to the topic, allowing developers to specify Net Zero targets alongside other certifications like BREEAM or LEED.

Key features of the standard include:

• Embodied carbon limits for construction.
• Minimum targets on renewable electricity generation.
• Verification of measured data post-occupancy.

Arnold says: ‘we’ve seen a lot of buildings already claiming to be Net Zero but often based on inconsistent methodology or only including operational emissions. The NZCBS puts an end to that.’

He adds: ‘We wanted a standard that could help us define the steps for a building to achieve Net Zero. But we also wanted it to cover all aspects of a building’s life cycle, so that everyone involved in a project – from the financier, developer or engineer – had an industry-backed and trusted standard to simplify the entire process.

‘It’s an industry game changer because it can be used as a benchmark for providing preferential rates; while developers can reference it when putting projects out to tender.’

Each development will need to be occupied for a year before enough data can be collected to verify it is aligned with the standard.

The role of the National Planning Policy Framework (NPPF)

Arnold has also urged the government to consider the role the NPPF can play in consolidating WLCAs. ‘While regulation is the only way to robustly control these emissions at the point of construction, the NPPF pays a key role in ensuring that planning proposals are low carbon. It must also enable local authorities to require higher standards on embodied carbon than national policy requires, as many authorities have pledged to reach Net Zero well ahead of the national 2050 target.’

With this in mind, he, alongside the other Part Z authors, has recommended updates to the document that go above and beyond what’s already been amended in the sustainability section. He’s required that explicit reference should be made to both embodied carbon and whole life carbon, strengthening the existing vague language on ‘mitigating climate change’. On planning applications, he’s suggested: ‘local planning authorities should expect new developments to: measure and report the embodied carbon related to the development involved and demonstrate how this has been reduced in accordance with industry best practices.’ It should also be updated to weigh embodied carbon alongside the existing text on energy efficiency.

Arnold also highlights the potential of repurposing vacant properties in urban centres, especially where there is existing infrastructure, reducing both carbon emissions and costs. Policies encouraging retrofit over new builds could align with carbon reduction goals while revitalising town centres.

Conclusion

It is right that the government make sure the regulation of whole life carbon assessments in the UK do not cause delay to house building projects or lead to disproportionate costs for SMEs. However, the UK’s construction sector has the expertise, motivation and tools to lead on the reduction of embodied carbon emissions. Clear regulations, coupled with industry commitment, could contribute to the government’s Net Zero targets, boost economic growth and ensure a sustainable future. Incorporating Part Z into existing building regulations would be a positive step forward this year towards achieving this.

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^{(1) UKGBC Net Zero Roadmap report – here}