Nature, climate and risk in NEC’s revised Option X29
August 2026Environmental requirements in construction contracts and governance frameworks are becoming more measurable, commercially significant and enforceable. Infrastructure delivery, maintenance and decommissioning have significant implications for greenhouse gas emissions, resource use, biodiversity and climate resilience, attracting increasing scrutiny from clients, investors, regulators and the wider public. NEC’s 2026 update to Option X29 of the NEC4 suite (X29) reflects that trend.
Originally developed to address climate-related obligations, X29 was expanded in June 2026 to recognise nature alongside climate. Supported by a Practice Note on the NEC4 Engineering and Construction Contract (ECC) and related guidance materials [1], the update reflects a shift beyond carbon reduction towards broader climate resilience and nature and biodiversity objectives. Below we consider the ECC and the NEC4 Professional Services Contract (PSC).
Original X29
Our earlier article on X29 examined the key elements of X29 and the changes it introduced across the NEC4 suite of contracts.
The introduction of X29 was viewed as a positive step in supporting the industry’s response to climate change, although the devil was very much in the detail.
The latest update is evolutionary rather than revolutionary. While the changes are largely terminological, they may have significant practical implications by enabling employers to use X29 to drive broader environmental outcomes through contractual targets and financial incentives.
Not just a climate clause
The revised clause widens X29’s terminology to incorporate nature and biodiversity alongside climate objectives. It introduces concepts such as Nature and Climate Requirements (Requirements), a Nature and Climate Plan (Plan) and Nature and Climate Partners (Partners), while retaining established NEC mechanisms including collaboration, early warnings, compensation events and performance measurement.
X29 creates contractual obligations against which performance can be measured, and the 2026 amendments extend that framework to “nature”. The Plan should set out the Consultant’s or Contractor’s approach to meeting the Requirements contained in the Scope. As a result, environmental obligations may assume a more central operational and commercial role in project delivery. NEC’s guidance notes that the level of detail should be proportionate to the scale and environmental sensitivity of the project.
Environmental agenda
Carbon reduction remains important, supported by guidance on whole-life carbon baselines, carbon optioneering, reporting and alignment with PAS 2080:2023. However, the revised guidance also addresses biodiversity net gain, habitat connectivity, sustainable drainage, soil reuse and ecosystem services, reflecting NEC’s intention that climate and nature objectives should be managed within a single contractual framework.
As a result, project teams may be required to monitor, evidence and report against a broader range of environmental measures than under traditional carbon-focused initiatives. Expanded disclosure provisions have been introduced in X29.5 allowing information to be publicised by the Parties for any purposes set out in the Requirements. The basis on which this can be used should be considered carefully, including understanding whether they enable Parties to evidence Scope 1-3 emissions as required.
Influencing design decisions
A feature highlighted in the guidance is the nature and climate hierarchy. Project teams are encouraged to consider nature-based solutions first, followed by nature-positive infrastructure, hybrid solutions and, where necessary, conventional engineered approaches. Carbon optimisation principles apply throughout and should be evidenced at agreed gateways.
The hierarchy is not expressly mentioned in X29 but is intended to influence procurement and design decisions. For example, project teams are encouraged by the NEC guidance to consider whether flood management objectives may be achieved through wetlands or other nature-based interventions before defaulting to traditional engineered solutions. Equally, where engineered solutions are required, the guidance encourages consideration of lower-carbon materials, reduced material use and alternative construction methodologies.
The Flowchart accompanying the guidance illustrates how the hierarchy interacts with the Plan, Performance Table and NEC administration processes throughout the project lifecycle. It offers a suggested framework for applying X29 from project inception to Completion, but must be adapted to reflect the particular project.
Consultant’s and Contractor’s proposals
The recent amendments broaden NEC4 ECC X29.11. The underlying obligation is unchanged but now sits within a wider environmental framework (including nature). In particular:
- Contractor may propose changes to reduce the impacts of creating, operating, maintaining or demolishing the works on nature and climate; and
- supporting quotation and analysis must address nature and climate impacts and items outlined.
The implications should be considered when developing and implementing Contractor’s proposals.
Many contractors will also rely on supply chain information to demonstrate compliance with contractual requirements. Failures to provide it may affect performance assessments and, where relevant, payment.
The NEC4 PSC X29.11 contains a similar (albeit more limited) requirement in that the Consultant may propose Scope changes to reduce the impact of the service or its results on nature and climate.
Performance Table
As with the original X29, a key issue for contractors and consultants is the optional Performance Table, which links environmental performance directly to contractual incentives and deductions.
Any potential deductions should be considered carefully and, where possible, capped. NEC guidance generally suggests that environmental incentives of 2% to 5% of contract value may be sufficient to influence behaviour. Particular attention should be given to how performance will be measured, the evidence required and the treatment of factors outside the Consultant’s or Contractor’s control, particularly where biodiversity-related outcomes are involved.
Any amounts payable under the Performance Table should be considered carefully. They fall outside any agreed liability cap and depending on the drafting of the mechanism, Performance Table deductions may also operate in a manner broadly comparable to liquidated damages and could fall outside standard professional indemnity insurance cover.
Requirements
The Practice Note recommends outcome-based requirements and advises against prescribing materials or methods unless necessary. While this promotes flexibility, contractors and consultants should carefully review the assumptions underpinning environmental targets and assessment methodologies. Poorly drafted outcome-based requirements increase the risk of dispute and obligations being construed as performance-based or fitness-for-purpose obligations, potentially creating exposure beyond that typically covered by professional indemnity insurance.
There is also the obligation to collaborate with Partners, although X29 does not automatically transfer risk to those parties. The extent to which collaboration is required will be stated in the Requirements, which again underlines why these should be considered carefully to understand the extent to which more formal collaboration and risk sharing is envisaged. The Consultant or Contractor may therefore carry performance risk without having full control over the relevant outcome.
Contractual drafting
The new X29 will not apply automatically by selection of X29 in the Contract Data. It will therefore be important to be clear which X29 applies and for entries in the Contract Data to reflect the updated version (and terminology) if that is being used.
In practice, the original X29 is sometimes incorporated without the supporting requirements, metrics and governance arrangements needed for it to operate effectively. However, the clause only works where Requirements are properly defined and set out.
The future
The expanded X29 reflects growing expectations from clients, regulators, funders and other stakeholders for measurable environmental outcomes. Extending the clause to nature as well as climate is a logical and welcome development without fundamentally altering the contractual mechanisms previously introduced.
However, the principal lesson from the original X29 remains unchanged: environmental obligations are only as effective as the contractual and commercial mechanisms supporting their use and implementation. Contractors and consultants should therefore focus on three key questions: who carries the risk, how performance will be measured and what commercial consequences will follow if targets are not achieved.
If you would like support in addressing the new guidance and clause wording in your contracts, please contact the authors.
[1] NEC expands Option X29 to put nature alongside climate in a major industry milestone | NEC Contracts, 6 July 2026
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