What is quantum in a construction claim?

Every construction claim splits into two questions: liability, whether something happened that entitles you to more money or time, and quantum, the Latin the industry kept, meaning how much. Quantum is the valuation half: pricing varied work from the contract's own rules, building up the cost of disruption from allocation sheets and outputs, valuing prolongation, the time related cost of being on site longer, and tying every figure to a record that proves it was spent and a cause that links it to the event. It is a different discipline from delay analysis, which sequences programmes to prove time, and the two are often done by different people; my own practice is quantum only. The distinction matters because claims fail on the two halves differently: a claim can win on liability and still collect a fraction of its number because the quantum was assertion rather than build up, and no amount of eloquent narrative rescues an unevidenced figure. When an assessor or adjudicator says the quantum is weak, they mean the money does not prove itself, whatever the merits of the story.

Say a subcontractor claims £120,000 for disruption after months of out of sequence working. Liability is strong: instructions, revised drawings and site minutes all show the employer's team drove the churn. But the £120,000 is one line, actual labour cost minus tendered labour cost, with nothing tying the overspend to the disruption rather than to its own estimating or productivity. An assessor accepts the entitlement and awards £40,000 on a broad brush, because the quantum never proved more. The same records built the other way, gang allocations against affected areas, outputs before and during the disrupted period, would have carried three times the number. The lesson is that liability opens the door and quantum decides what walks through it.