What is Part Z?
Part Z is a proposed amendment to UK Building Regulations that would require measurement and reporting of whole-life carbon emissions for new buildings above a certain size threshold. Unlike existing regulations that focus on operational energy (Part L), Part Z addresses the embodied carbon of construction materials - the emissions from extraction, manufacturing, transport, and construction.
The proposal, championed by the Part Z campaign group and supported by organisations including LETI, RIBA, and the UKGBC, has gained significant cross-party parliamentary support.
What would it require?
Based on the latest proposals, Part Z would initially require:
Whole-life carbon assessment: Projects above the threshold must calculate and report their total carbon impact across all lifecycle stages (Modules A1–C4, with Module D reported separately).
Upfront carbon limits: Mandatory maximum limits on Modules A1–A5 (product and construction stage), with limits tightening over time.
The initial threshold is expected to apply to buildings over 1,000m² or residential developments of 10+ units. This targets the projects with the greatest impact while giving smaller builders time to adapt.
Timeline and current status
Part Z is progressing through parliamentary stages. While the exact timeline depends on legislative scheduling, the current expectation is:
2025–2026: Consultation and parliamentary progress, with reporting requirements beginning for large projects.
2027–2028: Expected introduction of mandatory embodied carbon limits.
The government has signalled strong support for whole-life carbon regulation, and the UKNZCBS (UK Net Zero Carbon Building Standard) launched in early 2026 provides a complementary voluntary framework.
What it means for developers
For developers, Part Z means embodied carbon must now factor into feasibility studies and land appraisals. Material choices that were previously driven purely by cost and programme will need to account for carbon performance. Developers should begin requiring whole-life carbon assessments from their design teams now, even before Part Z becomes mandatory, to understand their carbon baseline and identify reduction opportunities.
What it means for architects and engineers
Design teams will need competency in whole-life carbon assessment. The RIBA Plan of Work already includes sustainability checkpoints, but Part Z makes these legally binding for qualifying projects. Architects and structural engineers should be able to demonstrate how design decisions - material selection, structural system, building form - influence embodied carbon. Tools like OneClick LCA and our Carbon Calculator can help quantify these trade-offs early in the design process.
What it means for contractors
Contractors will need to demonstrate that as-built carbon matches or improves on the design-stage assessment. This means tracking actual materials delivered to site, managing substitutions carefully, and reporting construction-stage emissions (Module A5). Procurement teams will increasingly need to source materials with EPDs and prioritise lower-carbon options.
Key Takeaways
- Part Z will require whole-life carbon measurement and reporting for large projects
- Mandatory upfront carbon limits (A1–A5) will follow, tightening over time
- Projects over 1,000m² or 10+ homes are likely in the initial scope
- The design team, not just the contractor, carries responsibility
- Start measuring now to understand your baseline before it becomes mandatory
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