The contractor's productivity on the same work, before and during the disruption, is the record that turns lost hours into money.
A measured mile compares the contractor's productivity on the same work in an unimpacted period with its productivity in the impacted one, and prices the hours lost at the difference. On an illustrative drylining package, 4.00 m2 an hour before the disruption against 3.00 after, adjusted for harder floors and the contractor's own rework, the claim is 656.1 hours, or 30,180. The total cost method, measured against the tender, would claim 55,200.
Worked in full in Construction Cost Control by Julian R. Sterling, with every figure reproduced in a free workbook.See the book on Amazon →
Disruption is lost productivity: the work gets done, but it takes more hours than it should because of something the client carries, late information, out-of-sequence access, trades stacked on the same floor. Unlike prolongation, there is no weekly rate to multiply. The loss has to be shown from the contractor's own records, and the measured mile is the method that does this with the least assumption: the contractor is compared with itself, on the same job, in the same trade.
| Input | Value |
|---|---|
| Unimpacted period, floors 2 to 4: area completed, m2 | 4,600 |
| Unimpacted period: operative hours | 1,150 |
| Impacted period, floors 5 to 8: area completed, m2 | 12,600 |
| Impacted period: operative hours | 4,200 |
| Tender output, typical floors, m2 per hour | 4.20 |
| Tender output, upper floors with more bathroom pods and shafts, m2 per hour | 3.86 |
| Hours of the contractor's own rework in the impacted period | 120 |
| All-in cost per operative hour | 46.00 |
The impacted period is the one in which, on the record, the client's late services coordination drawings forced the drylining gangs to work around incomplete risers and return to finished areas. The unimpacted period is floors 2 to 4, completed before the drawings were late.
Step 1: the two productivity rates. Unimpacted: 4,600 ÷ 1,150 = 4.00 m2 an hour. Impacted: 12,600 ÷ 4,200 = 3.00 m2 an hour. Productivity fell by 25.0 per cent.
Step 2: the hours the impacted work should have taken. At the unimpacted rate, 12,600 ÷ 4.00 = 3,150 hours. The raw loss is 4,200 − 3,150 = 1,050 hours, 48,300 at 46.00. That is the number that usually appears first, and it is not yet a claim.
Step 3: make the comparison like for like. The upper floors are harder work: the contractor's own tender priced them at 3.86 m2 an hour against 4.20 on typical floors, a ratio of 0.92. Applying that ratio to the measured rate gives an expected upper-floor output of 4.00 × 0.92 = 3.68 m2 an hour.
Lost hours = actual hours − impacted quantity ÷ (unimpacted rate × complexity factor) − contractor's own hours
= 4,200 − 12,600 ÷ 3.68 − 120 = 4,200 − 3,423.9 − 120 = 656.1 hours
Value = 656.1 × 46.00 = 30,180
In Excel, with impacted hours in B5, impacted m2 in B4, unimpacted m2 and hours in B2 and B3, the factor in B7 and own hours in B8: =(B5-B4/(B2/B3*B7)-B8)*B9, the hourly cost in B9.
Step 4: take out the contractor's own losses. The allocation sheets record 120 hours of rework on boards damaged by the contractor's own follow-on trades. Those hours sit in the impacted period but are not the client's risk, so they come off. What remains, 656.1 hours, is 15.6 per cent of the hours actually worked in the impacted period.
| Step | Hours | Value |
|---|---|---|
| Raw measured mile, no adjustment | 1,050.0 | 48,300 |
| After the 0.92 complexity factor | 776.1 | 35,700 |
| After removing 120 hours of own rework | 656.1 | 30,180 |
| Total cost method, against the tender rate | 1,200 | 55,200 |
The total cost method takes the tender output of 4.20 as the benchmark: 12,600 ÷ 4.20 = 3,000 hours expected, 1,200 lost. It overstates the defensible claim by 25,020, or 82.9 per cent, because it charges the client for three things the client did not cause: the harder floors, the contractor's own rework, and a tender that was 5.0 per cent more optimistic than the gangs ever achieved, even on the good floors.
The Society of Construction Law's Delay and Disruption Protocol prefers project-specific productivity comparisons, of which the measured mile is the best known, to industry studies or to total cost claims. It works only if the records exist: daily hours by gang and by area, and the area completed. Without them, there is nothing to measure.
| Complexity factor | No own hours | 120 own hours | 240 own hours |
|---|---|---|---|
| 0.88 | 28,541 | 23,021 | 17,501 |
| 0.92 | 35,700 | 30,180 | 24,660 |
| 0.96 | 42,262 | 36,742 | 31,222 |
| 1.00 | 48,300 | 42,780 | 37,260 |
Each step of 0.04 on the complexity factor moves the claim by between 6,038 and 7,159, more than another 120 hours of own rework would, at 5,520. The factor is where the argument will be, and it is strongest when it comes from the contractor's own tender build-up, as here, rather than from a judgment made after the dispute began.
The choice of unimpacted window matters as much. If the good floors averaged 3.80 m2 an hour, the claim falls to 475.9 hours and 21,891; at 4.20 it rises to 819.1 hours and 37,680. A window chosen because it shows the best week of the job will be attacked, and should be.
The common mistake is to treat the tender as the measured mile. A tender rate is a price, not a record of what the gang could do on this job, and any gap between the two that existed before the disruption is the contractor's risk. The client's quantity surveyor should ask first for the unimpacted rate actually achieved, then for the evidence behind any complexity factor, then for the rework log. Each one usually takes a slice off the claim, and together they took 45.3 per cent off this one.
The book traces disruption, prolongation and every other line of a final account back to inputs that existed at signature, and the free workbook for this case on the Construction Cost Control companion page runs the productivity loss as one of its sensitivities. The time-related side of the same delay is priced in how to calculate prolongation costs for an extension of time.
It measures lost productivity by comparing the same contractor, on the same work and the same project, in a period without disruption and a period with it. In the worked case drylining ran at 4.00 m2 an hour on unaffected floors and 3.00 on affected ones; after adjustments the loss is 656.1 hours, priced at 30,180.
It assumes the tender was achievable and that every overrun was the client's fault. Measured against a tender rate of 4.20 m2 an hour the drylining claim is 1,200 hours and 55,200, which includes harder floors, the contractor's own rework and a tender 5.0 per cent more optimistic than the gangs ever achieved.
Use the closest comparable: another floor, another trade gang, or a similar earlier project of the same contractor, adjusted for differences, and accept that the claim weakens. The adjustment itself carries weight: here a complexity factor between 0.88 and 1.00 moves the claim from 23,021 to 42,780.
This article is one calculation from Construction Cost Control. The book takes the same case from first principles to the decision, chapter by chapter, and every figure it prints is a live formula in the free companion workbooks.
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