While weather disruption is nothing new, changing climate patterns are reshaping the UK construction industry. Conditions once considered exceptional are becoming more common, raising questions about whether existing contractual mechanisms remain fit for purpose. To reduce uncertainty and potential disputes, parties should consider updating their contracts to protect against weather-related risks and delays.
UK weather
In 2026 the UK recorded 33 days above 30 degrees Celsius, with temperatures reaching 35 degrees Celsius in May, June, July, and August for the first time on record. The economic consequences were significant. Verdant, a UK thinktank, estimates that the heatwaves resulted in an economic loss of £4.4 billion. That figure is supported by research from the Grantham Research Institute on Climate Change and the Environment, which found that the June heatwave alone cost the UK economy £1.15 billion. This disruption was also felt across the workforce, with an estimated 24 million working hours lost in June.
As temperatures continue to rise and heatwaves become more frequent, the construction industry faces increasing challenges. Prolonged periods of extreme heat can impact site productivity, increase health and safety risks, and affect the performance, handling, and operation of construction materials and equipment.
But the challenges don’t end there. Forecasts suggest that the UK could experience stronger winds, heavier rainfall, and sudden drops in temperature this autumn and winter and while the effects of El Niño on UK weather remain uncertain, such conditions may create further difficulties for contractors and developers.
Persistent rainfall can cause flooding, water damage, and unstable ground conditions, disturbing excavation and foundation work. Combined with high winds that restrict lifting operations and other critical construction activities, these weather events have the potential to cause significant delays, increase costs, and place additional strain on project delivery.
Contractual position
JCT
Under clause 2.26.10 of the unamended JCT Design and Build Contract 2024, “exceptionally adverse weather” is a Relevant Event, which entitles the contractor to an extension of time, and relief from liquidated damages, where the project is delayed. In practice, however, establishing that weather is exceptionally adverse is difficult, because the contract does not define the term, leaving parties to rely on the limited case law available.
Sometimes, parties may agree to amend the contract to state that weather conditions are exceptionally adverse when they result in significant flooding or render a site inaccessible. In other circumstances, however, there may be some debate as to when weather becomes exceptionally adverse, rather than just adverse.
During the summer heatwaves, construction workers experienced increased fatigue, dehydration and reduced concentration, affecting both productivity and site safety. Despite this, there is no statutory maximum temperature at which construction work must cease in England and Wales. Belgium, for example, follows maximum working temperatures (on a wet bulb globe temperature basis) ranging from 18 degrees Celsius for very heavy work and 29 degrees Celsius for light work. In Spain, extreme weather events prompted the introduction of paid “climate leave”, where workers can take up to four days’ leave to avoid travelling during weather emergencies. It remains to be seen whether the UK will follow in introducing statutory working temperatures.
However, guidance issued by the Health and Safety Executive places clear responsibilities on employers and contractors to assess and manage heat-related risks. Compliance with those obligations may require contractors to adapt site operations, for example, by introducing flexible working arrangements, increasing rest breaks, or providing weather appropriate Personal Protective Equipment (PPE), all of which can affect programme delivery.
Therefore, as heatwaves become more frequent, the question is whether the threshold for exceptionally adverse weather remains fit for purpose, or if it needs to evolve to reflect our changing climate.
Also, while exceptionally adverse weather is a Relevant Event, it is not a Relevant Matter. This means the contractor is entitled to additional time, but not additional money. Any loss and expense arising from the delay must be absorbed by the contractor, including increased labour, plant, and site overhead costs, and it may also face claims from its supply chain.
NEC
Alternatively, the unamended NEC4 Engineering and Construction Contract uses “Compensation Events” to deal with both time and money claims. Under clause 60(13), a compensation event arises where adverse weather is recorded at the weather station identified in the Contract Data and the relevant weather measurement:
- is recorded within a calendar month;
- occurs before the Completion Date; and
- is compared against historical weather data for the stated location.
The weather event must also be one that, based on historical data, is expected to occur less frequently than once in ten years. Unlike the JCT, the NEC4 seeks to reduce ambiguity by relying on measurable weather data. However, as climate change continues to alter weather patterns, the construction industry may need to consider whether new contractual provisions are required, or whether employers will simply bear the inevitable increases in cost and programme contingencies that contractors are likely to include in their tenders.
Practical considerations
As extreme weather events become more common, conditions that were once considered exceptional may become part of the new normal, making it increasingly difficult to separate foreseeable weather risks and genuinely exceptional events.
Looking ahead, construction contracts may need to evolve to allocate weather-related risks more clearly and realistically between the parties. Some practical considerations include:
1. Project scheduling
Weather delays are usually associated with the winter months, typically December to February. However, weather disruption is no longer confined to a single season, with extreme heat, flooding, and storms creating the potential for delays throughout a much larger proportion of the construction programme. This means contractors may have to rethink project start times and working practices, including site operating hours and shift patterns, to protect productivity and worker welfare.
2. Construction programmes
Construction programmes are likely to come under greater scrutiny as weather-related risks increase. Contractors may need to be more transparent about the contingency periods built into their programmes and explain how weather risks have been factored into project delivery. Contractors may also start adopting a more cautious approach to planning, allowing additional time within programmes to account for potential disruption to the site and supply chain.
3. Weather monitoring
Weather is often localised and can vary considerably between locations. In mountainous and exposed areas, conditions can change quickly and may differ substantially from those experienced elsewhere in the region. This is difficult because it is not only the weather experienced on site that may affect progress, but also weather conditions in the surrounding area, which can influence site access, ground conditions, and supply chains. As a result, the selection of the weather station is important, and parties should ensure that the chosen weather station accurately reflects the conditions likely to affect the project.
4. Drafting
Historically, employers have amended the JCT Design and Build and NEC4 contracts to remove weather-related provisions, with contractors accepting the associated risk. However, as weather events become more frequent and severe, contractors may be less willing to assume that risk and instead seek to retain the standard provisions or negotiate alternative processes for managing weather risk. Where no contractual entitlement exists in respect of adverse weather, contractors may seek to protect themselves through longer programme durations and increased contingency allowances.
For further information about the issues raised in this article, please contact a member of our construction team.
Natalie is a Principal Associate in our Construction team. Natalie is an experienced construction lawyer specialising in all aspects of construction and development projects, from initial procure... Read More
Isobel is a Solicitor in our Construction team. She joined Capital Law in September 2024, completing her training contract and qualifying into our Construction team in July 2026. Isobel studied L... Read More
