Heat-related risks and claims in construction
July 2026Takeaways
- Recent rising temperatures cause concern for building owners and create risks for project design and delivery.
- Standard industry form contracts were not drafted for heat-related disruption, creating uncertainty around risk allocation and relief entitlements.
- Parties should review their approach to contracts and operations to mitigate future claims exposure.
UK infrastructure was historically built for a climate that no longer exists. As temperatures rise and heatwaves become more frequent and severe, the construction industry faces growing challenges. Although UK law does not prescribe a maximum working temperature1, heat impacts productivity, site safety, equipment and material performance, and the long-term resilience of assets. It also gives rise to legal, commercial and operational risks, including claims and disputes.
Standard contract provisions and design assumptions are largely based on historic weather patterns and may no longer provide adequate protection. Parties should review contracts, specifications, governance policies and risk assessments to address heat-related risks as noted below.
Increasing heat-related claims?
Extreme heat has become an increasingly significant factor on construction projects. Higher temperatures2 can lead to reduced labour productivity, mandatory hydration and rest breaks, fire risk on site or transport routes, site safety restrictions, delays or defects affecting temperature-sensitive activities (such as concrete pouring and curing, and application of asphalt and adhesives), and disruption to resource deployment, logistics or programme sequencing.
Accordingly, contractors may seek to pursue extension of time (EOT) claims for heat-related disruption, though entitlement will depend on the contract terms.
Standard industry forms provide limited protection:
- JCT: Contractors may claim additional time for “exceptionally adverse weather conditions” as a Relevant Event3. The heat aspect is undefined, and no temperature threshold applies. Additional costs from reduced productivity, temporary working arrangements or suspended operations are generally irrecoverable.
- NEC: The weather-related compensation event regime may provide time and cost relief, although the Contract Data may require amendment to address heat-specific risks. Where the prescribed weather measurement test is met and evidenced (typically comparing actual site weather data against a 10-year average), parties may be entitled to additional time and/or cost.4
- FIDIC: Entitlement depends on whether the event delaying completion was “exceptionally adverse” and “unforeseeable having regard to climatic data”5.
The bar for each of these is quite high. As heatwaves become more frequent, it may become harder to characterise such events as “exceptional”. Parties should review force majeure, relief events, change in law and insurance provisions to ensure heat-related risks are clearly anticipated, assessed and allocated.
Heat also creates broader governance risks. Failure to implement appropriate site controls may expose dutyholders to regulatory enforcement, personal injury claims and reputational damage. Prolonged drought can cause shrinkage and subsidence, particularly in clay soils, creating material risks for foundations, drainage systems and below-ground infrastructure and increasing the impact of unforeseen ground conditions.
Substantiating claims
Even if it can be established that temperatures meet the contractual threshold, this will generally not be enough. Contractors will typically need to demonstrate compliance with notice requirements, adherence to relevant government or industry guidance, a clear causal link between the heat event and project impacts, the extent of resulting delay and mitigation measures taken to reduce disruption.
Showing that heat has caused delay is likely to be the most difficult element. Unlike rainfall, where effects can be more tangible (such as flooding or conditions making specific work impossible), heat-related causation may be harder to establish in the absence of government guidance or recommendations.
Robust contemporaneous records are critical. Site diaries, weather data, photographs, progress reports and delay analyses often underpin entitlement. Project-specific weather monitoring, local data or agreed baseline measurements can improve certainty and reduce later evidential disputes. Where heatwaves are expected, it will be important to discuss the impact and potential mitigation measures with the employer and subcontractors at an early stage and seek to agree a way forward.
Design liability
Designers are increasingly expected to deliver assets that comply with evolving standards, meet sustainability objectives and remain resilient throughout their design life. Potential future claims may arise from alleged failures to address evolving climate-related risks, design for vulnerable occupants, comply with applicable standards (i.e. Building Regulations Approved Document Part O), incorporate appropriate adaptation or retrofit measures, or warn clients of foreseeable issues.
Design life assumptions, environmental exposure criteria and resilience requirements may become areas of dispute. Where contracts impose outcome-based or performance requirements relating to design life or climate resilience, such obligations may be outside the scope of professional indemnity insurance and should be carefully considered during procurement and contract negotiation.
Contract drafting
Construction contracts were traditionally drafted against assumptions derived from past weather patterns, but those benchmarks may no longer be reliable. To reduce uncertainty, parties should consider bespoke provisions addressing trigger events and temperature thresholds for heat-related EOT entitlement, notice and evidential requirements, mitigation obligations, and cost or commercial consequences. Obligations linked to design life, climate resilience or ground conditions should also be considered carefully.
Looking ahead
Claims relating to weather-related delay and disruption, additional cost, defects, performance failures and professional negligence may increase as temperatures rise and environmental conditions change. For contractors, consultants and insurers, the key issue is no longer whether climate-related risks will affect projects, but whether those risks have been appropriately identified, allocated and managed.
It is important to consider heat-related risks when drafting and negotiating contracts, to manage them proactively during a project, and to take them into account in approaches to design and programme planning. If you wish to discuss the impact of heatwave risks on your projects or contracts, please contact the authors
1 UK legislation requires indoor workplace temperatures to be ‘reasonable’ (i.e. Workplace (Health, Safety and Welfare) Regulations 1992). For outdoor sites, HSE guidance requires employers to undertake suitable risk assessments and implement appropriate controls during periods of excessive heat. Factors including air temperature, humidity, heat sources, work rate, ventilation, and clothing or PPE influences heat risk.
2 WMO confirms 2025 was one of warmest years on record, Press release, 14 January 2026
3 See Relevant Event in Clause 2.26.10 of the JCT Design & Build, 2024 Edition
4 See compensation event under Clause 60.1(13) NEC4, 2017 Edition
5 For example, Clause 8.5 (c) FIDIC Red Book and Yellow Book, 2017 Edition
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