Expert article
Site diary: obligation, contents, evidential value — what really has to go in
For the site supervisor, the site diary is a basic service of service phase 8 of the German HOAI ('Leistungsphase 8', the fee and service structure for architects and engineers) — whoever fails to keep it risks a fee reduction and loses the most important piece of evidence in a dispute.
Expert article by Open Experience GmbH. · As of: July 2026
What is the site diary?
The site diary is the continuous documentation of events on the construction site. For the site supervisor, it is a basic service of HOAI service phase 8. At a minimum, each working day's entry includes: date and weather, companies present with headcount, work performed, deliveries, disruptions, instructions, and special occurrences. What decides its evidential value is that it is kept promptly and continuously — not reconstructed after the fact.
Is the site diary mandatory?
For architects and engineers in site supervision: yes — owed as a basic service of service phase 8 as soon as that phase is commissioned. For executing companies, documentation obligations can arise from the construction contract (such as daily reports under VOB/B, the German construction contract procedures, or by contractual agreement); in public contracts, daily construction reports are regularly required.
What belongs in the site diary?
Eight mandatory contents — and why every single one counts in a dispute.
| Content | Why it counts |
|---|---|
| Date and day of the week | Placement in the construction sequence |
| *Weather* (temperature, precipitation, wind) | Disruptions, concrete pours, proof of construction time |
| Companies present and headcount | Proof of work performed, questions of delay |
| Work performed per trade | The actual construction progress |
| Deliveries and equipment deployment | Proof of logistics and performance |
| Disruptions and interruptions | Basis for construction time extensions |
| Instructions and directives | Who ordered what, and when |
| Special occurrences | Accidents, findings, visits — the memory of the construction site |
Who keeps the site diary — and how often?
The site supervisor keeps it continuously — in practice that means: one entry per working day, created promptly. A diary reconstructed weeks later loses its evidential value; that is exactly what courts and experts check first. Delegating to the site management on location is common; the responsibility stays with the site supervisor.
Digital or paper?
Both are permissible — what matters is completeness, continuity, and traceability. The digital site diary has three evidential advantages.
- Immutable timestampsEvery entry carries the time it was created — not the time it was written up.
- Automatic weather dataMeasurements from your own construction site instead of a forecast "somewhere in the region" — decisive in disruption claims.
- Linked to photosReport and picture from the same day and place stay together — the chain of evidence holds.
On paper, all of that is assertion; digitally, it is proof.
The five most common mistakes
Written after the fact
Entries in one batch at the end of the month — worthless in a dispute.
Weather forgotten
Of all things, the column that decides construction time disputes.
"All normal"
Without companies, headcount, and work performed, the day is not documented.
Disruptions only reported verbally
What isn't in the diary didn't disrupt anything.
No link to photos
Report here, pictures there — the chain of evidence breaks.
How to do it better
Daily report done mobile on the construction site: weather automatic, photos linked, timestamps immutable, distribution included.
The daily report that almost writes itself
With Construction Diary, our site diary app, the entry is created where the working day happens: weather data comes from your own station, photos from the same site walk, and distribution to the owner and all parties happens at the push of a button.
Frequently asked questions
Does the site diary belong to the owner?
It is part of the services owed in service phase 8 — the client is entitled to the documentation.
Are photos enough instead of a diary?
No — photos prove conditions, the diary proves sequences, attendance, and events. Together they are strong.
How long do I have to keep the site diary?
At least beyond the warranty period; because of possible secondary liability, considerably longer is recommended.
What distinguishes the site diary from the daily construction report?
The daily report is the individual day's entry (often from the contractor); the site diary is the continuous overall documentation of site supervision.
Can the subcontractor supply their own daily reports?
Yes — and it pays off for both sides: their proof of work, your complete file. The accounts for this are free.
Keep the site diary without typing in the evening.
45 minutes on your project — including the question of how the reports reach the owner.