Disruption and productivity loss: prove the changed work

The chain a disruption claim needs

1. An attributable event changed working conditions.
2. The change affected identifiable resources doing identifiable work.
3. Productivity fell because of that change rather than for another reason.
4. The loss can be measured reliably.
5. The contract and the governing law permit recovery.

Start with production, not the overrun

The fact that labour hours exceeded the estimate proves nothing. The estimate may have been low. The scope may have grown. Supervision may have failed. Crews may have been inexperienced. Rework, weather, absenteeism, sequencing or subcontractor default may explain a large part of it.

Instead, take a work package and ask what changed. Restricted access forced smaller work fronts. Late design caused stop and start installation. Staggered material release broke the planned sequence. Repeated changes caused demobilisation and relearning. For each, map the instruction or condition to location, dates, crews, quantities and observed consequences.

Measured mile

A measured mile compares productivity in an impacted period or area against reasonably comparable unimpacted performance on the same project. Its strength is that it reduces reliance on tender assumptions. Its weakness is comparability, and comparability is where these claims are won and lost.

Test scope, design, crew mix, learning curve, location, height, weather, shift, supervision, tools, congestion, quantities and timing. An unimpacted period doing different work is not a control simply because its output was higher.

Judgment Amey LG Ltd v Cumbria County Council [2016] EWHC 2856 (TCC) is generally cited as a warning that the label does not resolve the comparator and alternative-cause problems. Cited here for that practical proposition only.

When there is no clean mile

Say so. A modified comparison may be possible with the adjustments exposed. Work sampling, crew studies, earned value, contemporaneous estimates or carefully selected industry studies may assist as corroboration. No method should be used to hide weak project records, and a transparent factual analysis beats a precise-looking model built on data that will not bear it.

Total cost and modified total cost

A total-cost claim subtracts tender cost from actual cost and attributes the difference. That arithmetic is not causal proof. A modified approach removes identified claimant-caused and unrelated amounts, but still depends on a reliable bid, reasonable actual cost, established responsibility and the impracticability of more direct measurement. These claims are treated with suspicion for good reason.

Evidence checklist

• Contract entitlement and timely notice.
• A defined event, workface, period and affected trade.
• The baseline method and planned sequence.
• Labour and plant input matched to installed output.
• Crew, location, shift and condition data.
• Contemporaneous reports describing the mechanism, not the blame.
• A comparable unimpacted period, or an explained alternative method.
• Analysis of scope growth, rework, weather, learning, supervision and contractor causes.
• Actual cost reconciliation and mitigation.
• An overlap matrix preventing duplicate recovery.