NEC4 Optional Clause X1

NEC3 and NEC4 Contracts General
1

Currently managing an NEC4 Option A with Clause X1 selected.

The indicies used is the BCIS TPI. This is often updated retrospectively, so an individual index can change from being forecast to provisional to final over the course of a number of months.

I appreciate that once an adjustment is made that’s not changed and that for the assessment index you use the index that is published on that date.

However, what if the base index changes between assessments. So for example when you undertook assessment 1 the index was 300 and you used this in your calculations. However, when you undertook assessment 2 the index for the same period had been updated and was 302.

Do you use 302 in the assessment 2 calculations or 300? And where is this clearly stated in the contract or guidance?

2

My interpretation (with the usual caveat about Z Clauses) is that the calculation is not changed.

My reasoning is as follows:

  • In Clause X1.1, there are definitions for two indices, the Base Date Index and the Latest Index.
  • Clause X1.2 says “If an index is changed”, if the intention had been for this to apply only to the Latest Index, it would have said “If a Latest Index is changed”.
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