Chapter 02
Weather claims substantiation
How to substantiate a weather claim with time-aligned site capture, a recognised meteorological source, and contemporaneous notes that hold against an assessor who has seen every shape of weather argument before.
01
Why most weather claims fail
Most weather claims fail not because the weather did not happen but because the claim cannot show that the weather affected the activity on the critical path. A rainfall report shows that it rained. A schedule extract shows that an external activity was scheduled. Without a captured view of the work front during the period, the assessor has to take on faith that the activity could not proceed. That assessment loses more often than it wins, particularly in jurisdictions where the assessor is expected to apply a documented baseline of expected adverse weather days. The substantiation requires a third source — site capture — that closes the loop between the meteorological event and the disturbance to the activity. The other recurring failure is the use of unrecognised weather data. A reading from a phone application or an unattended weather station on the hoarding will not survive challenge if the assessor has access to a Met Office or equivalent national service record. The discipline is to use the recognised source from the start so the data origin is never the contested point. The contractor who builds the file on a recognised source from day one writes a much shorter response when the weather record is challenged.
02
The contractual frame for weather
The treatment of exceptionally adverse weather varies by contract form, and the framing of the claim has to match the form in use. Under JCT, exceptionally adverse weather is a relevant event but typically not a relevant matter, which means time but no money. Under NEC, weather is a compensation event only if it occurs less frequently than once in ten years, which puts the burden on the contractor to demonstrate the rarity against historical data. Under FIDIC, the position depends on which sub-clauses are amended and on the particular conditions of the contract. The first task on receipt of any weather event is therefore to read the relevant clause carefully and identify what the contract treats as weather, what threshold has to be crossed, and what notice is required. A weather notice that argues for time and money under a JCT contract that gives only time is a notice that wastes the project´s credibility. The discipline is to claim only what the contract permits and to evidence the claim in the form the contract envisages. The same discipline applies to subcontracts; an upstream weather entitlement is not automatically a downstream entitlement, and the back-to-back position has to be checked at the moment the notice is contemplated.
03
The three-source test
A defensible weather claim uses three time-aligned sources. The weather record from a recognised source — a national meteorological service rather than a phone app or an unattended station. The site capture showing the work front during the period, ideally with both fixed-camera coverage and a 360 walk on the day. The schedule extract showing the activity that was supposed to be in progress, with the predecessor and successor visible in the same view. When the three sources align, the claim narrative writes itself: the weather was there, the work front was empty, the activity was on the path. When the three sources do not align, the project knows the claim is weaker than it looks before the formal notice goes out. That is a useful signal, even when the answer is to withdraw the claim. The team that runs the three-source test as a habit on every wet day spends less time on weak claims and more time on strong ones. The pattern that emerges across a contract is also useful evidence in itself; a contractor who can show that the project ran the test consistently is harder to challenge on selective citation than one who only produces the test when it suits.
04
Building the file at the time
The file should open the day the stand-down occurs, not the day the notice goes out. A short note in the diary, a tagged clip from the relevant view, a printed weather record from the source the team uses by default, and a programme extract dated at the moment. Five minutes of work that day prevents five hours of reconstruction six months later. Most weather claim weakness is the gap between those two moments. A simple discipline that works on most projects is the wet-day register: a single page per event, completed at the close of the affected shift, with the four artefacts attached and a one-line entry in the daily diary that cross-references the register entry. The register sits in the claims evidence folder rather than the diary, but the diary points to it. When the formal notice is later considered, the register entries become the index of the claim. The claim is not invented at notice time; it is curated from a stack of contemporaneous entries that have been waiting for the decision. Practitioners who run the register report that the decision to claim or not to claim becomes substantially clearer when the cumulative evidence is visible at a glance.
Practice
01. For your current project, write down the recognised weather source the team will cite in any weather notice and the contract clause under which exceptional weather is treated.
Look for: A strong response names a national meteorological service or comparable accepted source, identifies the relevant contract clause and threshold (for example NEC compensation event for once-in-ten-year frequency), and notes who on the team is responsible for retrieving the record.
02. Open the wet-day register or equivalent for the past month. List any days where the three-source test cannot be completed and note what is missing.
Look for: A strong response identifies the missing artefact for each day (weather record, site capture, or programme extract), states whether the gap is recoverable, and proposes a single change to close future gaps.
Checkpoint
Pick a wet day from this month. Can you produce the three sources, time-aligned, in under ten minutes, and identify the contract clause under which the entitlement would be claimed?
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