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Cutting through the legalese: “exceptionally adverse weather”

“I’m dreaming of a White Christmas… just like the ones we used to know”.

So does that mean that snow is now unusual?  How much snow does there need to be before the contractor gets an extension of time? 

Whilst most sensible programmers will have allowed for a certain amount of cold weather this winter, what happens when the unexpected happens, weather-wise?  It’s all very well and good saying that we should expect snow in the winter but of course an official “White Christmas” merely requires the falling of a single snowflake at the Met Office in London at some point in the 24 hours of 25 December and that is actually rarer than rocking-reindeer-sh….. anyway, suffice it to say it’s hardly enough to stop construction works (even if it were a Working Day)!

 So what exactly gets you an extension of time anyway?


Contract type




“exceptionally adverse weather conditions”

There is nothing in the guidance to help and very little by way of judicial interpretation.  It is generally considered to be different from “normal” adverse weather.  Amendments are often made to bring the assessment closer to NEC methods (1 in 10 year).


“A weather measurement is recorded:

  • ·         Within a calendar month,
  • ·         Before the Completion Date for the whole of the works and
  • ·         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.”

There are clear, prescriptive and objective data and measurement details in the Contract Data that can be agreed by the parties. 


It is worth noting that it only deals with rain, cold and snow (i.e., it does not deal with extreme heat or wind).


“exceptionally severe weather conditions or the consequences thereof” (as part of Force Majeure”

Similar to JCT – ends up being a matter for the Engineer to consider in the circumstances.


“exceptionally adverse climatic conditions”

Similar to JCT – ends up being a matter for the Engineer to consider in the circumstances.

Whilst NEC may be too prescriptive for some, we would recommend making amendments to JCT, IChemE and FIDIC contracts to give greater objectivity.  Setting the boundaries at the drafting stage could save a lot of difficulty at final account stage. 

Finally, it is worth noting that all building contracts are usually quite prescriptive about timescales and contents of notices to be given where weather may cause a delay.  You should always check your contract (and any bespoke amendments) as a matter of urgency so as not to risk being time-barred in a claim for extension of time.

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These notes have been prepared for the purpose of an article only. They should not be regarded as a substitute for taking legal advice

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