Expert article
Weather in the site diary: what counts once there is a dispute
"Rain, work stopped" is a sentence, not a record. What a weather entry has to carry to still be worth something months later.
Expert article by Open Experience GmbH. As of: September 2026
Which weather details belong in the daily site report?
For every working day the daily site report should carry at least temperature, precipitation and wind — sensibly with the time of day and the way conditions developed, not as a single figure — together with the consequences that followed: which activities were affected, which trades, from when and for how long. The decisive part is the link between the two: the weather situation on its own is a footnote; only the documented effect on specific activities turns it into a usable record. A weather entry evidences the conditions people worked under — in itself it does not establish any claim to an extension of time or to payment.
Legal framework: Germany (Civil Code BGB, construction contract rules VOB/B, fee schedule HOAI). Other countries have different rules, and contractual agreements take precedence over the standard periods named here.
Four details that a robust entry contains
What separates a note about the weather from an entry you can actually use is not its length but the way it is tied to the work.
- Reading with a timeTemperature, precipitation and wind with a time reference — morning, midday, afternoon, or as a curve over the day. A single daily figure leaves open whether it actually rained during the working hours in question.
- Place of measurementThe site itself or a reference station, and how far away that station sits. With showers and gusts, there is a considerable difference between a station at the building and a reading taken 20 kilometres away.
- Affected activity and tradeNot "work obstructed", but which task on which building element could not be carried out because of which condition.
- Duration and consequenceFrom when, until when, with what result — interruption, rescheduling, rework, plant or personnel standing idle.
Rule of thumb: someone reading the entry a year later must understand without asking why no work was done that day.
When the weather actually stops the work
Typical orders of magnitude taken from codes of practice and manufacturers' specifications. What binds you is always the specific product, manufacturer or equipment requirement — the table replaces no assessment of the individual case, it shows which values are worth recording in the first place.
| Activity | Critical condition | What to record |
|---|---|---|
| Concreting | Frost, low fresh concrete and air temperature | Air temperature across the day, fresh concrete temperature, measures taken (covering, heating) |
| Screed, plaster, painting | Temperature below the workable limit, high humidity | Room and element temperature, humidity, drying times |
| Crane operation and erection | Wind speed and gusts above the manufacturer's clearance | Peak gusts with times, moment of shutdown, lifts affected |
| Waterproofing, roofing, bitumen | Wet conditions, proximity to dew point, moisture in the substrate | Precipitation with duration, moisture in the element, interruption times |
| Earthworks, foundations | Persistent rain, softened ground, frost in the formation level | Total precipitation over several days, condition of the formation level |
| Outdoor work in general | Storm, thunderstorm, heat | Warning situation, time of evacuation, instruction by site management |
What a weather entry proves — and what it does not
This is where documentation and entitlement part company. That distinction is why carefully kept daily site reports make the difference in a dispute without being the claim themselves.
- The entry evidences the conditionsIt records what prevailed on the working day and what followed from it. That finding of fact is precisely what nobody can reconstruct later.
- Not every weather event is an obstructionUnder § 6 of VOB/B (the German construction contract procedures), weather conditions that had normally to be expected when the tender was submitted do not count as an obstruction. What matters is therefore the departure from the usual — and that only becomes visible against long-term figures.
- Giving notice is a duty in its own rightAn obstruction must be notified in writing without undue delay; the site diary does not replace that notice. It supplies the facts behind it.
- Claims have their own preconditionsWhether an extension of time, compensation under § 642 of the German Civil Code or an adjustment of payment comes into question depends on the contract, on causation and on the notice given — not on the weather alone.
This article describes documentation practice; it is no substitute for legal advice in an individual case.
Reading, forecast, reference station — three different things
The most common weakness in weather documentation is not missing weather but the confusion of these three sources.
- Reading taken on siteA station on or beside the site measures the conditions that actually occurred. That is the most robust basis for looking back at a single working day.
- Reference data from the weather serviceStation records and climate archives — such as those of the German Meteorological Service (DWD) — are the way to answer the question of what is "usual": did the period depart from the long-term average?
- ForecastA forecast estimates conditions to come. It is valuable for planning the work and unsuitable as retrospective evidence.
In practice: carrying a forecast in the daily site report as though it were a reading weakens the entire documentation — including the entries that are correct.
How Open Experience solves this
Construction Weather feeds the readings into Construction Diary automatically; which stations and which data appear in the daily report is something you set per project. The weather then no longer sits alongside as a separate list but in the same report as the affected activities, photographs and people on site.
- Local readings instead of regional weatherAs our weather partner, Cordulus supplies stations and measurement data for the project location — including historical figures for looking back.
- One report, one contextWeather, work carried out, obstructions and photographs all arise in the same daily report. Nobody has to establish the link that matters later after the fact.
Further reading
Site diary — duty, contents, evidential value
The overview article: who has to keep a site diary, what belongs in it, and where its evidential value fails in practice?
To the guideCordulus as weather partner
Weather stations, historical readings and local forecasts for the site — and how that connects with Construction Weather.
To the partner pageFrequently asked questions
Is recording the weather in the site diary mandatory?
For site supervision under the HOAI, keeping a site diary is a basic service of service phase 8, and the weather is one of its classic contents. For contractors the duty follows from the construction contract; on public contracts daily site reports are regularly required. Either way, without a weather entry you later lack the basis for any discussion about weather-related interruptions.
Is the weather app on my phone enough?
For planning the work, yes; as evidence, no. An app usually shows a forecast or a regional observation, often without a documented time reference and without naming the measuring point. For looking back you need traceable readings with place and time — or reference data from a named station.
How accurate does the measurement have to be?
What matters is less the decimal place than the traceability: where does the figure come from, when was it recorded, how far away is the measuring point? A station at the building has the advantage over a distant reference above all with showers, gusts and local frost.
Do documented bad-weather days justify an extension of time?
Not automatically. Under § 6 of VOB/B, weather conditions that had to be expected when the tender was submitted do not count as an obstruction; on top of that come notice without undue delay and proof of the specific effect on the construction sequence. The documentation supplies the facts; the assessment follows from the contract and the circumstances.
How long should weather data be kept?
Sensibly for as long as the rest of the project records, at least until the warranty periods have expired — disputes about weather-related defects or delays rarely arise during construction, but years later.
Sources and legal basis
The legal statements in this article are based on the primary sources listed below. The article is not a substitute for legal advice in an individual case.
- VOB/B (2016 edition), official text of the German Federal Ministry for Housing (BMWSB) — Section 6: obstruction and interruption of the works
- Section 642 German Civil Code (BGB) — compensation where the client fails to cooperate
- HOAI, Annex 10.1 — basic services of service phase 8, including keeping a site diary
- German Meteorological Service (DWD) — climate data archive of daily and monthly values Reference for the question whether a weather situation departs from the long-term average.
- Cordulus Construction — weather stations and weather data for construction sites
Make the weather part of your documentation.
In the demo you see, at your own project location, how readings reach the daily report — and what that is worth in a dispute.