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As heatwaves and wildfires become more common, parties may need to revisit whether traditional weather provisions are allocating risk in the way they intended.
As another summer of heatwaves and wildfires draws to a close, many in the construction industry will be hoping for cooler temperatures ahead. The events of recent months also provide an opportunity to reflect on wider questions. Construction contracts have long dealt with weather risk. However, are they equipped to deal with disruption that does not stop work altogether? What about weather events that instead make projects slower, more difficult and more expensive to deliver?
Extreme heat can affect labour productivity, working hours, welfare arrangements, plant and temperature-sensitive materials. Unlike flooding or severe storms, effects are often gradual, making it harder to identify when contractual entitlement arises and who should bear the resulting risk.
What does the contract say?
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JCT: familiar wording, uncertain outcome
JCT allows contractors to claim an extension of time for "exceptionally adverse weather conditions". However, the term is undefined and there is no specified temperature threshold. Whether a particular heatwave is sufficiently “exceptional” depends on the available facts and evidence. Generally, one will look to weather conditions over the preceding 10 years. It is also worth remembering that under an unamended JCT contract, "exceptionally adverse weather conditions" entitles a contractor to additional time but not additional money.
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NEC: an objective test
NEC takes a more data-driven approach by comparing actual weather data against historical records. If the contractual thresholds are met, weather may constitute a compensation event, potentially giving rise to both time and money. The default Contract Data Part One in an NEC contract includes measuring the number of days less than 0 degrees Celsius but, so far, it is not common to see additional measurements included for the number of days exceeding, say, 30 degrees Celsius. Therefore, projects where heat is a material risk may benefit from more tailored provisions.
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FIDIC: is heat unforeseeable?
FIDIC uses the term "exceptionally adverse climatic conditions" that are unforeseeable having regard to the available climatic data. Parties may find it difficult to argue that conditions were genuinely unforeseeable, particularly as extreme heat becomes more common. The question to bear in mind is not whether temperatures are high but whether they are outside what could reasonably have been anticipated when the contract was entered into.
Heat does not always stop the works
There is no fixed maximum temperature at which construction work in the UK must automatically stop[1]. Instead, health and safety duties require employers and contractors to assess and control the risks according to the conditions, activity being undertaken, length of exposure, PPE required and mitigation measures available.
Work may continue, at a reduced output, through revised working hours, additional breaks, welfare measures or changes to temperature-sensitive activities.
The temperature alone is unlikely to establish an entitlement under the contract. Even if the high temperature is a qualifying event entitling a contractor to claim, it will also need to demonstrate that this extreme heat affected activities on the critical path and resulted in delay to the date for completion. For example, it may be difficult to prove that workers took longer to carry out a task due to the difficulties in working in high temperatures rather than simply being less productive for a few days. This makes record-keeping even more important.
Time is only half the story
Whether additional cost is recoverable will depend on the terms of the contract and how the project responds to the heat. A contractor's decision to alter its working arrangements may be treated differently from an instruction from the employer or project manager revising methods, sequencing or working hours. Parties should therefore be clear about who is making operational decisions, under which contractual power and with what consequences.
Recurring heat also raises a broader pricing question. While an isolated weather event may be priced to some extent, repeated periods of reduced productivity may be harder to account for, particularly on long-term projects where the contractor bears the risk of anticipated weather conditions. Do you need to build the cost of procuring additional shelters for shaded working or fans into the price?
What is happening downstream?
Although main contracts and subcontracts often containbroadly back-to-back weather provisions, they may not operate in the same wayin practice. A subcontractor may experience heat-related delay or reducedproductivity even where the site remains operational and the main contractorhas no equivalent entitlement upstream.
Parties should consider whether:
- weather relief and notice provisions operate consistently throughout the contractual chain; and
- package-level delay and productivity impacts can be properly evidenced.
A general flow-down provision may not be appropriate and, as with other risk allocation issues, the drafting needs to work in practice rather than simply replicate the upstream wording. This is particularly important where heat-related disruption develops gradually over time, as a delay in notifying a subcontract claim could prevent the main contractor from preserving a corresponding entitlement under the main contract.
Wildfires: a different set of risks
Although closely associated with extreme heat, wildfires may present a different category of risk. It may result in site evacuation, loss of access, disruption to transport and supply chains or interruption to essential services. Depending on the circumstances, this may engage contractual provisions beyond adverse weather clauses (e.g., force majeure).
For projects near woodland, heathland, grassland or moorland, or where key materials are sourced from areas with a known wildfire risk, parties may wish to address the issue expressly rather than rely on general contractual provisions.
Draft now, evidence later
Not every project needs a bespoke heatwave regime. However, parties should consider:
- how heat-related events will be defined and measured;
- whether relief extends to time, money or both; and
- how productivity impacts and wildfire risks will be addressed.
Any contractual provisions should be supported by contemporaneous records, including site weather data, labour and productivity records, site diaries, programme updates and evidence of mitigation measures.
Conclusion
Adverse weather provisions are not new but the type ofdisruption they are being asked to manage is changing.
Where extreme heat or wildfires is a material project risk,clear drafting, aligned notices and contemporaneous records may be moreeffective than trying to fit gradual, activity-specific disruption intoprovisions developed with very different weather conditions in mind.
Footnotes
[1] In July 2026, Green Party MP Hannah Spencer introduced the Maximum Workplace Temperature Bill as a Private Member's Bill. Rather than setting a temperature limit itself, the Bill would establish an independent body to recommend maximum safe workplace temperatures and advise the government on implementation.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
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