Disruption is not prolongation

Prolongation is about time: the site was open longer, so it cost more to run. Disruption is about productivity: the same work took more resource than it should have, because of the way it was interfered with.

They are frequently claimed together and they are not the same thing. Crucially, disruption can occur with no delay to completion whatsoever, and a claim that requires an extension of time as a precondition has confused the two.

What causes it

Out-of-sequence working, where trades follow each other in an order nobody planned. Trade stacking, where too many operatives work in a space designed for fewer. Repeated interruption, where a gang stops and restarts. Late information, where work proceeds in fragments as details arrive.

None of these necessarily moves the completion date. All of them make the work cost more.

Why it is hard to prove

Because the loss is the difference between what happened and what would have happened, and only one of those two things is observable.

The contractor knows it used twelve thousand labour hours. It has to establish that the work should have taken nine thousand, that the difference was caused by the employer’s events rather than its own performance or its own optimistic tender, and that the events in question are relevant matters.

The methods

Several approaches are used, and their credibility varies considerably.

• Measured mile. Compare productivity in an undisrupted period on the same project with productivity in the disrupted period. Generally the most persuasive, because the comparison controls for the site, the labour and the design.
• Comparison with a similar project. Weaker, because no two projects are alike enough to isolate the variable.
• Industry studies. Published factors for trade stacking, overtime and similar. Usually treated as supporting material rather than proof.
• Total cost. Claiming the difference between tendered and actual cost. Rarely accepted, because it assumes the tender was correct and that every overrun was the employer’s fault.

The records that make it possible

Allocation sheets recording who worked where and on what, day by day. Progress records showing what was actually achieved. Site diaries recording the conditions.

Without those, the measured mile cannot be constructed and the claim falls back on weaker methods. This is the single clearest case in construction where the quality of routine record keeping directly determines whether money is recoverable.

Getting it into the account

Notify when the disruption is occurring, not when the account is being prepared. Identify the events. Keep the labour records separately for the affected areas if you can.

A disruption claim assembled at the end from monthly cost reports is an argument about who was inefficient. One assembled from contemporaneous allocation records is a calculation.