What does NEC4 clause 60.1(13) mean?

It replaces arguments about bad weather with a measurement. The measurement must be recorded within a calendar month, before the Completion Date for the whole of the works, at the place the Contract Data states. Compared with the weather data, it must be shown to occur on average less often than once in 10 years. The Contract Data names the place and the measurements to be recorded, such as total rainfall or days with snow lying. It also names the source of the weather data. To prove the event, get the recorded measurement for the month, and the once-in-10-years value for that measurement and month. Then show the recorded value is worse. Weather at a different place, a measurement the Contract Data does not list, or a bad fortnight in an ordinary month do not count. You only know once the month's record is available. That is when you become aware, and you notify under clause 61.3 within 8 weeks of it. The change to the Prices, your contract price, is assessed under clause 63.1. It is the effect on actual Defined Cost up to the notification and forecast Defined Cost after it, plus the Fee. Clause 60.1(13) itself limits the assessment to the difference between the measurement and the once-in-10-years weather. So you are paid only for the excess over a once-in-10-years month. Two things go wrong most. You claim for every wet day. Or you cannot separate the cost of the excess days from the days you should have allowed for. Any delay to the Completion Date is assessed separately under clause 63, and that is a job for your planner.