Couple of points here:
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NEC does not use the language “extension of time”. Each and every compensation event has to be considered in terms of time impact and the cost agreed within that quotation, and the agreement of time delay to Completion Date (and/or sectional completions or Key Dates).
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Weather is one of the items in the list within clause 60.1, but only when it exceeds a “1 in 10 year event” for which you can get the local met office data as to what is a one in ten year event for rain, snow and freezing temperatures. If it exceeds that value in a calendar month then yes it is a compensation event. The tricky bit is proving what the effect is, as only the element that exceeded the 1 in 10 year event is a compensation event.