James So
- Associate
- Construction
Here comes the sun and I say “it’s not alright”
As extreme weather events become more frequent and severe, businesses involved in construction and development projects face increasing uncertainty around delay risk and contractual responsibility. Traditional assumptions about what constitutes “exceptionally adverse weather” may no longer hold. Parties should consider reviewing and updating construction contracts to define weather-related delay thresholds clearly, reducing the risk of costly disputes uncertainty as climate patterns continue to shift.
In recent years, we have seen extreme weather events becoming more frequent, longer lasting and more intense.
While warm spells in the UK have lengthened materially in recent decades, the 2026 El Niño event is set to be an unprecedented weather pattern resulting in increased rainfall and storms for the UK this autumn.
For construction projects, the consequences of such extreme weather may include delay due to adverse weather conditions as a result of reduced working periods, changes to sequencing and restrictions on temperature-sensitive operations. In this article, we look at how exceptionally adverse weather is treated through the JCT Design and Build Contract 2024.
Weather Delays – Contractual Starting Point
Under the unamended JCT Design and Build Contract 2024, “exceptionally adverse weather conditions” are a Relevant Event under clause 2.26.10. If completion is likely to be delayed beyond the existing Completion Date, the Contractor must notify the Employer when the delay becomes reasonably apparent, provide particulars of the delay and its impact and estimate the length of the expected delay. Exceptionally adverse weather is not itself a Relevant Matter, so an extension of time ordinarily relieves the Contractor from liquidated damages for the qualifying period but does not generate an automatic entitlement to any loss and expense caused by the delay.
When are weather conditions considered exceptionally adverse?
Because the JCT does not define the term “exceptionally adverse weather”, this will come down to the discretion of the Employer’s Agent. However, the focus will be on determining that weather conditions were “exceptionally” adverse. This typically requires reviewing historical data relevant to the site location. Tools such as the Met Office’s Downtime Report, which compares local observations with long-term averages for JCT purposes and provides daily data for multiple weather parameters, can be useful when weather conditions exceed these parameters.
Health and safety considerations can also be relevant when assessing whether a weather event is exceptionally adverse. In the case of heat, while there is no statutory maximum temperature (in the case of heatwaves) at which construction work must cease in England and Wales, employers and contractors have duties under the Health and Safety at Work etc. Act 1974 and associated regulations to assess and manage risks arising from excessive heat. This might include adjusting shift patterns, moving work to cooler parts of the day and suspending external works.
It’s important to note that neither of these factors on their own create an automatic entitlement to additional time.
Clarify through drafting
While the above is helpful in determining whether a weather event is exceptionally adverse, disputes can still arise if the threshold remains undefined. Therefore, we recommend parties clarifying what an exceptionally adverse weather event is in the JCT, possibly by referring to past measurements from the nearest Met Office and a tolerance level that needs to be exceeded e.g. in the case of heat where the daily maximum temperature exceeds the ten-year average for the site by more than a stated percent.
As certain weather conditions become more common each year e.g. more frequent and hotter heatwaves in the summer, the threshold for what is “exceptionally” adverse will change to adapt to long term trends.
Were the works affected?
The contractual question is not merely if the weather was exceptional, but whether it affected the execution of the works so that the date for completion was delayed. While potentially relevant to external works, where the suspension of critical path activities will delay completion, exceptionally high temperatures or extreme rainfall may have little or no effect on certain internal fit-out activities undertaken within climate-controlled environments e.g. office interiors. It’s worth noting, however, that while the works on site themselves might not be directly affected, if a contractor’s supply chain is experiencing issues due to exceptionally adverse weather, a contractor may apply for an extension of time. It is not entirely clear what would happen in this situation as there is no authority to suggest that the exceptionally adverse weather conditions have to be specific to the site of the works.
Before concluding that weather conditions have been exceptionally adverse enough to have delayed completion of the works, consideration should be given to whether mitigation measures were available, as an unamended JCT Design and Build Contract 2024 requires the Contractor to use its best endeavours to prevent delay in the progress of the works or any section. As this is a ‘best endeavours’ obligation, this may require expenditure on behalf of the Contractor without any ability to claim for loss and expense. Examples of reasonable weather mitigation may therefore include:
- Resequencing from exposed to internal or shaded work;
- Adjusting starts to cooler periods; and
- Protecting workfaces and materials.
Practical tips
When assessing a weather-related extension of time application, Employers and Employers’ Agents should ask four questions:
- Was the weather objectively exceptional for that location and time of year?
- Did the weather event satisfy the criteria under the contract (if any amendments were made)?
- Did health and safety requirements necessitate changes to the way the works were carried out?
- Did it materially affect the activities being undertaken?
- Were appropriate mitigation measures implemented?
- Did those effects actually delay the contractual Completion Date?
Only when all four questions can be answered positively is a weather event likely to qualify as an “exceptionally adverse weather” event capable of justifying an extension of time under the JCT Design and Build Contract.
While the above looks at the position within the JCT Design and Build Contract 2024, the position might be different for other forms of contract. For example, the NEC4 is much more prescriptive in how it determines whether a weather event results in a compensation event. Under the NEC4 form of contract a weather measurement has to be recorded:
- Within a calendar month;
- Before the Completion Date for the whole of the works;
- At the place stated in the Contract Data;
and compared with historical data showing that the weather measurement occurs, on average, less frequently than once in ten years. Only the difference between the actual weather measurement and the one-in-ten-year value is taken into account when assessing the compensation event.
Final thoughts
As heat related events increase, what is considered “exceptionally adverse” weather will continue to evolve. For project teams, the key is not predicting the weather but allocating and managing the risk of it. Clear contractual thresholds, good record-keeping and proactive mitigation can help ensure that, when the sun shines a little too fiercely, the contractual consequences are clearer for everyone involved.
This article is for general information purposes only and does not constitute legal advice or a comprehensive statement of the law. Specific legal advice should always be sought in relation to individual circumstances.
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