When the heat is on: extensions of time and extreme weather

In the UK, we all well recall the mini heatwave back in July. With further disruption from climate change likely, Taj Atwal looks at some of the key statutory and contractual issues that the construction industry needs to be aware of. 


Journalists were observing the temperature very carefully during the summer of 2022, waiting for the moment the temperature in the UK reached a new record high. And, in Lincolnshire on 19 July 2022, the temperature did just that, reaching 40.3 degrees.1 With schools closing and the government advising people to work from home where possible, there was yet more disruption to the construction industry.

There are measures available to mitigate the effects of usual high temperatures, but the inevitable question is: who pays? For example, one of the world’s oldest suspension bridges, Hammersmith Bridge, was wrapped in foil to keep cracks from spreading and ultimately destroying the development. A £420,000 temperature control system was installed so that the bridge could maintain a safe temperature. The system allowed the council and engineers to track and maintain the temperature and alleviate any stress on the pedestals.2

With climate change getting worse and the never-ending burning of fossil fuels, such as oil, gas and coal, the planet is heating up and it looks like heatwaves in the UK may become far more common. So, what might the construction industry need to be thinking about? 

Extreme heat and legislation 

Temperatures in the indoor workplace are governed by the Workplace (Health, Safety and Welfare) Regulations 1992.3 In addition, where reasonably practicable, assessments of the risks to health and safety are required under the Management of Health and Safety at Work Regulations 1999.4 However, putting it into perspective:

“There’s no maximum temperature because workplaces with hot processes such as bakeries or foundries would not be able to comply with such a regulation. They use other measures to control the effects of temperature. These other measures should also be used to manage the risk of working outdoors in a hot environment.”5

When there are high temperatures, the working environment needs to be properly controlled because heat is a hazard and can cause overheating and fire to flammable materials.

So, what can employers do to make working in hot weather safer? The Health and Safety Executive (HSE) issued guidance recommending that they should adhere to the following:6

  • provide sun protection advice in routine health and safety training; 
  • site water points and rest areas in the shade to encourage hydration; 
  • remind workers that they can remove personal protective equipment when resting. 
  • provided it is safe to do so, encourage workers to wear clothing that covers the skin including hats with a brim or flap that protects the ears and neck; 
  • remind workers to use sunscreen with a sun protection factor (SPF) of at least 15 on any exposed skin;
  • where practicable, schedule work to minimise exposure to heat and sun; and
  • encourage workers to check regularly for any unusual skin spots or moles.

A failure to provide a safe and healthy working environment may leave an employer at risk of possible prosecution. 

What do the contracts say? 

As well as protecting their workforce, employers and contractors need to consider where the risks of working in excessively hot temperatures lie in their contracts. 

JCT Contracts

Under the JCT standard forms, “exceptionally adverse weather conditions” are a relevant event which may entitle a contractor to an extension of time. However, the JCT does not define “exceptionally adverse weather conditions”. Therefore, the contractor will need to persuade the contract administrator that there is an entitlement.

Here, it is important to note that JCT have collaborated with the Met Office to provide two forms of weather reports: A Weather Planning Report and A Downtime Report. Both are designed to support claims for an extension of time and compensation under the JCT (and NEC) contracts.7

FIDIC 2017 Yellow Book 

The FIDIC 2017 Yellow Book provides more clarity on “exceptionally adverse climatic conditions”. Subclause 8.5(c) states:

“exceptionally adverse climatic conditions, which for the purpose of these Conditions shall mean adverse climatic conditions at the Site which are Unforeseeable having regard to climatic data made available by the Employer under Sub-Clause 2.5 [Site Data and Items of Reference] and/or climatic data published in the Country for the geographical location of the Site.”

Further, clause 2.5 requires an Employer to provide any information about the climate that is in its possession to the Contractor: 

“The Employer shall have made available to the Contractor for information, before the Base Date, all relevant data in the Employer’s possession on the topography of the Site and on sub-surface, hydrological, climatic, and environmental conditions at the Site. The Employer shall promptly make available to the Contractor all such data which comes into the Employer’s possession after the Base Date.”

FIDIC has also provided some limited guidance on what exceptional climatic conditions are. The 2000 FIDIC Guide suggests that: 

“it may be appropriate to compare the adverse climatic conditions with the frequency with which events of similar adversity have previously occurred at or near the Site. An exceptional degree of adversity might, for example, be regarded as one which has a probability of occurrence of four or five times the Time for Completion of the Works (for example, once every eight to ten years for a two-year contract).”

If you had a two-year contract, the UK summer heatwave of 2022 clearly falls within that definition.

NEC4 (2017)

The NEC4 Form provides more detail about when weather conditions might be considered to be suitably adverse to qualify as a compensation event. Sub-clause 60.1(13) states:

“A weather measurement is recorded:

  • within a calendar month, 
  • before the Completion Date for the whole of the works, 
  • at the place stated in the Contract Data,
  • the value of which, by comparison with the weather data, is shown to occur on average less frequently than once in ten years.

Only the difference between the weather measurement and the weather which the weather data show to occur on average less frequently than once in ten years is taken into account in assessing a compensation event.”

Clause 60.1(12) allows the Contractor to make a claim for a compensation event where adverse weather is recorded “within the Site”

NEC “seeks to define exactly what constitutes adverse weather by defining it as weather conditions that are shown, in comparison to local weather data recorded at a weather station identified in the Contract Data (which ideally should be the weather station closest to the site).”8 However, the Guidance Notes specify that “if there is not a weather station nearby, the weather measurements should be made using gauged and equipment installed at a place stated in the Contract Data9.

What records must be taken to qualify as a “compensation event”? Well, NEC suggests the following:

  • cumulative rainfall (mm);
  • number of days with rainfall more than 5mm;
  • number of days with minimum air temperature less than 0 degrees Celsius; and 
  • the number of days with snow lying on the ground at a time to be agreed by the Employer and the Contractor.

What is missing from these notes is any reference to the impact of high temperatures. A sign perhaps of the NEC’s UK origins. The Contractor must, therefore, fall back on the specific reference in the sub-clause to temperatures which “occur on average less frequently than once in ten years”.  

What can a Contractor do before making an extension of time claim?

  1. Look to see which party bears the risk for exceptionally adverse weather conditions. 
  2. Check the contract requirements and ensure that any notice is given in time and in the correct form. 
  3. Keep proper records of weather reports on site, where possible use the Met Office website. Be ready to compare the conditions encountered with those you would expect to encounter based on previous years. 
  4. Remember, it is not enough to simply say that it was hot, even if the temperatures were record-breaking. You must explain how the hot weather caused delay and/or led to disruption or the incurring of other additional costs. 


In the UK, we only tend to think about adverse weather in terms of snow, torrential rain or storms, but the summer of 2022 has shown that unusually high temperatures now may also need to be taken into consideration. As well as the risks to workers, parties need to consider the potential for increased fire hazards. When it comes to looking for relief under the standard forms, however, even if there is no specific mention of high temperatures, the approach to claiming time and money is no different whether there is a heatwave or prolonged snowstorm. 

Be guided by your contract and remember that, whilst it is tempting to concentrate on proving just how hot it was, it is just as important to demonstrate how that caused delay and/or additional cost. 

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