How may disruption be evaluated, and what is the measured-mile method?
The measured mile compares productivity on substantially similar unimpacted and impacted work. It can quantify lost productivity, but it does not establish contractual entitlement or prove which event caused the difference.
Use a like-for-like productivity comparison after proving the compensable disrupting event and affected work
Select an unimpacted baseline from the same project where possible. Compare the same work type, method, crew skill, location and maturity, using consistent units and hours. Remove learning curve, weather, design, access and contractor-responsible differences. If no valid measured mile exists, use a modified comparison, event-specific additional-resource analysis, reliable industry data or a reasoned assessment. Tender productivity and total-cost approaches require particular caution.
| Issue | Position |
|---|---|
| Entitlement | Identify compensable event and contractual route |
| Measured mile | Compare like unimpacted and impacted productivity |
| Causation | Remove non-compensable causes and confounding factors |
| Alternative analysis | Use event-specific hours, external benchmarks or reasoned assessment |
| Global overspend | Does not by itself prove disruption loss |
Disruption is productivity loss
Disruption concerns inefficient use of resources, not merely delayed completion. The contractor must identify what work was performed, the resources used, the expected reasonable productivity and how a compensable event changed that productivity.
Entitlement precedes measurement
A productivity comparison quantifies difference. It does not prove that the employer was responsible, that the event was compensable or that every difference resulted from it. Establish the causal event narrative first.
Separate tender error, learning curve, poor supervision, absenteeism, weather, access, rework and other contractor-risk causes before attributing loss.
Measured-mile method
Calculate units completed per labour hour, or labour hours per unit, for a demonstrably unimpacted period and the impacted work. Apply the supported productivity difference to the comparable impacted quantity, then value the resulting lost hours under the contract.
Comparability tests
| Test | Requirement |
|---|---|
| Work type | Same operation, specification and method. |
| Complexity | Comparable geometry, interfaces and quality demands. |
| Crew | Similar size, skill, supervision and learning stage. |
| Location | Comparable access, congestion and workface conditions. |
| Time conditions | Account for season, weather, shifts and fatigue. |
| Other events | Remove changes, defects and contractor inefficiency. |
Whittall Builders
Productivity during hindered dwelling work was compared with a later orderly period. The agreed production figures supported a practical percentage assessment of labour productivity loss.
Alternative event-specific schedules
Where no clean baseline exists, isolate extra labour and plant hours by event and activity, compare them with a supported no-event requirement, and present the calculation in traceable schedules.
Difficult quantum does not erase proven loss
A tribunal should make the best reasonable assessment where breach and actual loss are established but exact monetary measurement is difficult.
An estimated valuation was adopted where the owner's breaches caused loss but accurate proof of additional cost was impracticable.
Cost-less-recovery risk
A labour-cost-over-tender approach may be substantially reduced where the evidence does not show that all the excess cost arose from the matters relied on, or where it reveals inefficient use of labour.
Walter Lilly and causal proof
The court addressed disruption and global claims, confirming that causation remains essential. A claimant is not automatically barred because precise allocation is difficult, but material contractor-responsible causes and evidential gaps affect recovery.
Data and calculation
| Data | Control |
|---|---|
| Quantity | Installed units measured consistently. |
| Hours | Paid and productive hours reconciled to payroll. |
| Crew | Trade, skill, size and supervision. |
| Conditions | Location, access, weather, design and sequence. |
| Maturity | Learning curve and repetition stage. |
| Events | Dates and activities affected by each compensable cause. |
Practical sequence
Define the compensable disruption events.
Map each event to affected activities and dates.
Select a genuinely comparable unimpacted baseline.
Normalise quantity, hours, crews and conditions.
Calculate productivity difference and lost hours.
Remove contractor-risk and other confounding causes.
Use alternative assessment only with disclosed assumptions and sensitivity checks.
Authorities
| Authority | Citation | What it decides |
|---|---|---|
| Whittall Builders Co Ltd v Chester-le-Street District Council | (1987) 40 BLR 82 | A like-for-like project productivity comparison supported the recorded disruption award. |
| Chaplin v Hicks | [1911] 2 KB 786 | Proven loss may be reasonably assessed despite measurement difficulty. |
| Penvidic Contracting Co Ltd v International Nickel Co of Canada Ltd | (1975) 53 DLR (3d) 748 | Estimated damages were permitted where accurate proof was impracticable on the recorded facts. |
| Walter Lilly & Company Ltd v Mackay | [2012] EWHC 1773 (TCC) | Disruption recovery remained dependent on proof of causation despite allocation difficulty. |