Measured mile and disruption

Because they are proved with different records, and a delay analysis will not establish a disruption case however good it is.

The consequence is practical. If disruption is a realistic prospect on your project — and on any congested, heavily varied or accelerated job it is — the records that support it must be collected as the work happens. There is no equivalent of reconstructing a programme afterwards.

The strongest method available, and the reason is simple: it compares the project against itself.

The comparison removes almost every argument about whether the planned rate was ever achievable, because it does not use the planned rate. It uses what this crew, on this project, actually achieved when conditions were normal.

A worked example. In a clean period, a crew installs 4,200 m² of blockwork using 3,000 man-hours — 1.40 m² per man-hour. In the affected period, they install 3,100 m² using 3,400 man-hours — 0.91 m² per man-hour.

Every number in that calculation comes from a record made at the time. That is the whole strength of the method.

Five conditions. All five have to hold, and the other side will test each one.

1. Same work type. Blockwork against blockwork. Not blockwork against general finishing.
2. Same or comparable crew. A different subcontractor, or the same one after a large turnover, is a different comparison.
3. Same or comparable location and access. Ground floor against floor 34 is not a fair comparison — height, hoisting and congestion differ.
4. No significant impacts in the period. No major variation, no acceleration, no severe congestion, no abnormal weather.
5. Long enough to be representative. A single week captures noise. Several weeks, or a complete repeating cycle, captures performance.

Where no clean period exists at all — because the disruption started early and never stopped — the measured mile is unavailable and the method drops down the hierarchy. That drop is a real loss of evidential strength, and it is worth knowing early rather than discovering it in month thirty.

The bottom of that list is treated with considerable scepticism, and reasonably so: it asks the reader to accept that the tender was correct and that none of the overrun was the claimant's own doing. Modified total cost improves on it by deducting the claimant's own contribution, but the burden remains uncomfortable.

Everything above rank 3 requires project records at activity level. Which brings the page back to the same point as several others on this site.

Six records. None is difficult; all are worthless if started late.

• Daily labour allocation by activity and area. Not just total headcount on site. Which trade, how many, where, doing what. This is the single record that decides whether disruption can ever be quantified.
• Quantities installed by period and area, tied to the same breakdown as the labour.
• The instruction, variation and RFI log, with dates and affected areas.
• Site diaries covering access, congestion, weather and interference.
• Programme updates, archived — establishing what was planned in each period.
• Photographs, dated and located.

Activity granularity determines whether any of this is usable. Labour booked against a 90-day activity spanning six floors and three trades cannot be compared with anything. Booked against Blockwork L07 zone 2, it can. That is why activity size and duration limits is a commercial decision made at baseline, not a scheduling preference.