A site diary is the continuous, day-by-day record of what actually happens on a construction site. The German question bautagebuch pflicht, meaning whether a site diary is mandatory, is therefore not a formality. It affects whether dates, defects, instructions and delays can still be understood later.
When a site diary is required
HOAI, the German fee regulation for architects and engineers, defines service phases for planning services. In HOAI 2021, service phase 8, called LPH 8 in German practice, covers site supervision during execution. Site supervision means checking whether the works are carried out in line with permits, contracts, execution documents, regulations and generally accepted technical rules. When this service is commissioned, documentation of the construction process is part of the basic services, for example through a site diary.
For contractors, the position is different. VOB/B is the German set of general contract conditions for construction works, provided it has been validly agreed in the contract. VOB/B does not automatically require every contractor to keep a site diary. A duty can arise from the construction contract, special contract conditions, the bill of quantities or a clear instruction from the employer. In that case, daily reports or site reports become a contractual obligation.
For the responsible site manager under German state building law, additional organisational and supervision duties may apply depending on the federal state. Whether those duties require a site diary in a particular form depends on the applicable state law and the project. In practical terms, anyone who manages, supervises or later needs to support claims should not wait for a dispute before starting proper records.
What belongs in each daily entry
A daily entry is the individual site diary record for one calendar day or working day. It should be clear enough for a competent third party to reconstruct the day later.
- Project, date, author, inspection time and affected area of the building.
- Weather, temperature and relevant conditions such as frost, heat, heavy rain or wind, where they affect works, drying, safety or programme.
- Companies on site, workforce numbers, important equipment and notable downtime.
- Works performed, with location, element, axis, level or room.
- Deliveries, installed materials, samples, inspections and released drawing revisions.
- Mangel, a German construction defect meaning a deviation from the agreed condition, with exact location and photo reference.
- Behinderung, an obstruction or delay event that may affect proper execution, with start, cause and affected works.
- Anordnung, a binding instruction from the employer or an authorised representative, with time, content and recipient.
- Meetings, inspections, participants, outcomes and open points.
A site diary should not contain broad accusations, unmarked assumptions or personal data without a factual reason. DSGVO, the German term for the General Data Protection Regulation, governs the protection of personal data. Photos showing identifiable people, number plates or private items should only be stored if they are needed for the construction record.
A concrete daily example
Example: Tuesday, 5 May 2026, new office and workshop building, section B.
- Weather: 8 degrees Celsius in the morning, light rain until around 10:30, then dry. External works on the north side resumed at 11:15.
- Attendance: Company A with 6 workers, Company B with 3 workers, surveyor from 9:20, site supervision on site from 8:05 to 12:40.
- Execution: In level 1, service chases were closed in rooms B.1.04 to B.1.09. In staircase B, the substructure was continued. On visual inspection, the works correspond to released drawing A-203, revision C.
- Delivery: Three pallets of insulation boards arrived at 8:45. Packaging dry, storage in hall 2 on timber bearers. Delivery note recorded as photo 2026-05-05-03.
- Inspection: Moisture measurement in room B.1.07 documented at 10:10. Result forwarded to employer and Company B. Further work agreed only after release.
- Defect: Damaged connection edge identified in room B.1.05. Photo 2026-05-05-07, location axis 3/C. Company A informed at 10:35 and announced remedial work for the following day.
- Obstruction: Company B could not start in room B.1.12 because the released detail drawing for the connection was missing. Request sent to the design team at 9:55. Affected area: around 12 square metres of wall surface.
- Instruction: Employer representative released execution according to detail A-412, revision B, by email at 11:50. Start of execution planned for 6 May.
- Safety: Temporary fall protection at opening area B/2 was objected to and corrected at 12:20.
This example separates observation, decision and consequence. It does not replace a separate defect notice, obstruction notice or Bedenkenanmeldung. Bedenkenanmeldung is the German term for a contractor’s notice that the intended execution, supplied material or preceding work may be technically problematic.
Why it can count as evidence later
Evidential value means that a document can help establish facts in a later dispute. A site diary is generally not a court record and not automatic proof of everything it contains. It can, however, be useful evidence if it is created promptly, kept continuously, written specifically and free from contradictions.
Its evidential value increases when entries are linked to photos, drawing revisions, emails, delivery notes, measurements and minutes. Countersignature by a contractor or employer can also help. In digital systems, time stamps, version history and traceable user rights matter. Later changes should remain visible rather than silently replacing the original entry.
This is especially important for programme issues. A party alleging delay usually needs to show when the event began, whom it affected, why it arose and when it ended. For defects, the record helps capture location, timing, condition and reaction. For Nachträge, the German term for variations or additional claims, the daily entry may show whether and when an instruction was given. This does not replace legal assessment. It creates the factual basis for it.
Typical mistakes and limits
Many site diaries lose value because they are written too late or too generally. A sentence such as works proceeding to plan is of little help if the parties later argue about downtime, preceding works or quality. Photos without location, date and a clear link to the entry are also weak.
Typical mistakes are:
- Writing entries at the end of the month from memory.
- Recording activities without locations or building elements.
- Recording weather broadly although it affected the works.
- Noting defects without photo, deadline, recipient or next action.
- Recording instructions without clarifying sender and authority.
- Accepting AI-generated text without checking it.
Software can help, but it does not make the professional decision. It does not decide whether a claim exists, whether execution is defective or whether an instruction is payable. That remains the task of the responsible people and, where needed, legal advice. This article is technical guidance, not legal advice.
Keep it digital, but disciplined
A digital site diary is particularly useful when voice input, photos, tasks, drawing revisions and open points stay within one project context. The important point is that the daily report must not become a loose archive. Every entry needs date, location, responsible person, reference and outcome.
When artificial intelligence is used, meaning software that proposes content from speech, images or notes, those suggestions should remain recognisable and subject to professional review. KI-VO, the German term for the EU AI Act, contains transparency duties for certain AI systems in Article 50. For construction practice, this means AI may prepare content, but the responsible person must check, correct and release it.
In summary, the site diary duty is binding where site supervision has been commissioned or documentation has been contractually required. Regardless of that, a disciplined site diary protects the project routine because it records facts promptly instead of reconstructing them from memory.
Structify supports this workflow with mobile capture, voice input, photos, tasks and labelled AI suggestions that you can review and correct. Further site functions are available in Structify Mobile. If you want to see what this looks like on your project, book a short online demo.