Prolongation and disruption are the two principal heads in most loss and expense claims, they arise from similar events and they are proved in entirely different ways. Claims that treat them as one are the commonest structural failure in this area, which is why separating them comes early in loss and expense claim preparation.
The distinction is not academic. An assessor can deal with a prolongation claim from a programme and a resource schedule; a disruption claim needs quite different evidence.
What prolongation is
The cost of the site being open longer than planned: time related preliminaries, supervision, site establishment, plant retained.
It is measured against a period, which means it depends on establishing that the period was extended and by how much.
That makes it closely linked to the extension of time position, and usually assessed after it.
What disruption is
The cost of work taking more resource than it should have done, whether or not the project finished late.
It is measured against productivity rather than against time, which makes it independent of the completion date.
A project that finished on time can still carry a substantial disruption claim, and frequently does.
Why they get merged
Because they arise from the same events and the cost appears in the same accounts.
Because disruption is harder to evidence, so it gets folded into a prolongation claim where the evidence is easier.
And because a total cost approach captures both without distinguishing them, which is why total cost claims are attractive and weak.
Proving prolongation
Establish the extended period, from the programme and the extension of time position.
Identify the time related costs actually incurred in that period, by resource, from the accounts.
And show that those costs relate to the period rather than to the whole project, which is where tender allowances and actual costs have to be reconciled.
Proving disruption
Identify the activity affected, the period, and what happened to it.
Establish the productivity that was achieved and compare it with a baseline: the tender allowance, an unaffected period of the same work, or comparable work elsewhere.
And link the loss of productivity to the matter relied on rather than to everything that happened at the same time.
The evidence each needs
Prolongation: the programme and its updates, the preliminaries build up, and the actual costs for the extended period.
Disruption: labour and plant allocated to activities, output records, and the sequence as planned against the sequence as worked.
The second set is far less commonly kept, which is why disruption claims fail more often.
Double counting between them
The same preliminaries can appear in both, where the prolongation claim covers a period in which the disruption claim also sits.
Resources can be counted twice where a gang appears in a disruption calculation and in a prolongation resource schedule.
An assessor who finds one instance of double counting treats the rest of the claim with suspicion, which is why checking for it before submission is worth the time.
Double counting with variations
Where a variation valuation has already included an allowance for disruption to the varied work, claiming the same effect again under loss and expense is duplication.
Separating what the variation account covers from what remains is part of putting the claim together.
That separation is also what makes the remaining claim credible.
What a good structure looks like
Prolongation set out by period and by resource, tied to the extension of time position.
Disruption set out by activity, with the baseline stated and the comparison shown.
And a statement of what is excluded from each, so the assessor can see that the two do not overlap.
What to do when disruption cannot be proved
Say so, and claim what can be shown. A prolongation claim that stands up recovers more than a combined claim that collapses.
Where the records genuinely do not support a disruption calculation, that is worth establishing early rather than after weeks of work.
A claim scaled to the evidence is a stronger commercial position than a larger one that cannot be defended.
The order to prepare them in
Prolongation comes first, because it depends on the time position and the time position has to be established anyway. Once the extended period is settled, the time related cost for that period follows from the accounts with very little argument.
Disruption comes second, and what it can attempt depends on what the records turn out to support. Starting with disruption means spending the budget on the harder head before knowing whether it is provable, which is how claims end up unbalanced.
It also means the submission can be written in stages, with the prolongation part finished and capable of being put forward while the disruption analysis is still being tested against the records.
Acceleration, which is neither
Where the contractor was instructed to accelerate, or did so to mitigate, the cost of that is a third thing again: not the cost of being there longer and not the cost of working inefficiently, but the cost of working faster than planned.
Whether it is recoverable depends on whether it was instructed, and if it was not, on whether the contract supports a claim for mitigation measures taken without instruction. That is a point on which the contract wording matters more than the cost records do.
Claims frequently fold acceleration into disruption because the cost appears in the same accounts. Separating it is worth the effort, because the entitlement arguments for the two are entirely different.
Where it fits
The separation is structural and it is done at the start, before any cost is assembled.
Prolongation depends on the time position, which is extension of time work, and the two are usually prepared together.
The records that make both provable are kept during the project, as part of commercial management rather than in anticipation of a claim.
Costs incurred that nobody has agreed to pay?
Loss and expense claim preparation sets out the contractual provisions relied on, the costs actually incurred and the link between each matter and each head of cost, in a form that can be tested.