Extension of construction period & schedule verification: How can an extension of the deadline be verified? (VOB/B & BGB)
Bauzeitverlängerung richtig nachweisen:
On construction sites, deadlines are often ‘postponed’ informally – a sentence in a construction meeting, an email with a new schedule or a ‘we'll sort that out later’. However, when it comes to addenda, final invoices or disputes, it is no longer a question of who said what, but only of what can be verifiably proven. The decisive factors are the specific circumstances that caused the delay, whether this was reported in good time, how the event affected the construction process and in what way.
This article is a practical guide to professionally enforcing an extension of the construction period. It covers the legal basis according to VOB/B and BGB (German Construction Contract Procedures and Civil Code) as well as the requirements for reliable schedule verification. The text is for informational purposes only and does not constitute legal advice.
Clearly distinguish between contract terms and construction schedule
One of the most costly sources of error in large-scale projects is the confusion between contract deadlines and construction schedules. Contract deadlines are contractually binding dates, such as the start of construction, interim deadlines or the completion date. The construction schedule or timetable, on the other hand, is primarily an operational tool for managing the construction process.
According to the VOB/B system, dates from the construction schedule only become contractual deadlines if they have been expressly agreed as such. In practice, this means that the schedule is a key tool for project management, but the only dates that are relevant for claims for extension of the construction period are those that are contractually binding.
Extension of construction period according to VOB/B – obstruction pursuant to Section 6
Timely notification of obstruction as a key factor
If the contractor is prevented from performing the service properly, Section 6 VOB/B requires immediate written notification of the impediment. If this notification is not provided or is provided late, invoking the impediment as a defence is generally excluded. Exceptions only apply if the client was obviously aware of the cause and effects of the impediment.
Fristverlängerung bedeutet mehr als Stillstand
If there is an impediment within the sphere of influence of the client or another reason specified in § 6 VOB/B, the execution deadlines shall be extended. The duration of the standstill alone is not decisive in this regard. The effects on the resumption of work, on the construction sequence and possible postponements to a less favourable season with corresponding seasonal effects must also be taken into account.
Assess weather conditions correctly
According to VOB/B, normal weather conditions expected for the season are not automatically considered an impediment. An extension of the construction period can only be considered in the event of exceptional weather conditions that exceed the usual extent.
Obligations to cooperate and restart times
Verifiable evidence also includes demonstrating that the contractor took reasonable measures to mitigate the damage. This includes when it would have been possible to resume work and how long it realistically took to restart operations. In practice, direct downtime and secondary effects such as remobilisation are considered and assessed separately.
Extension of construction period for BGB contracts
In the case of contracts for work and services under the German Civil Code (BGB), there is no direct equivalent to Section 6 VOB/B. However, the logic behind the provision of evidence remains the same. The cause, duration and effects of the disruption on the construction process must be presented in a comprehensible manner.
Section 642 of the German Civil Code (BGB), which regulates the customer's obligation to cooperate, is particularly relevant. If this cooperation is not provided, the contractor can demand reasonable compensation. Under the BGB regime, early, factual notification of the disruption and clear, versioned documentation are also crucial in order to clearly record the start, duration and effects.
What is a schedule certificate?
A schedule verification proves that a specific impediment led to a schedule change on the critical path or that existing buffer times were completely used up, making an activity critical. Claims often fail because, although logs, emails and photos are available, no reliable connection can be established between the event, the affected activity in the schedule, the critical path and the actual deadline postponement.
Requirements for a verifiable extension of the construction period
For a claim to be valid, four points must be clearly and comprehensibly documented: the disruptive event with location, time and area of responsibility, timely notification and communication, the causal influence on the contractual deadline, and a realistic calculation of the construction time extension, including restart and, if applicable, seasonal effects.
What does a reliable schedule certificate look like?
Evidence that has been created promptly and clearly versioned is convincing. The basis for this is an approved baseline schedule with clear logic, defined milestones and a recognisable critical path. The actual construction process is regularly updated and documented with real start and end dates.
The so-called window approach is particularly informative. This involves comparing the target and actual status in defined time periods in order to show when and how an obstruction became critical. The evidence is supplemented by a construction log, photo documentation, meeting minutes and the currently valid plan or BIM status.
The Proof Pack for securing claims
An effective claim for an extension of the construction period must include at least one notification of hindrance and, ideally, a deregistration of the hindrance to define the time frame. In addition, there must be versioned schedule snapshots, a compact window overview, comprehensive construction site documentation, and evidence of mitigation measures taken and their limited effectiveness.
Common mistakes in enforcing deadline extensions
Typical errors include new schedules without a comprehensible methodology, lack of versioning, combining multiple faults in a single report, delayed notifications, and lack of evidence of damage mitigation.
Proven mini workflow for large projects
A tried-and-tested procedure consists of daily documentation on the construction site, immediate notification of any obstructions, weekly schedule updates with target/actual comparisons, deregistration of the obstruction once it has been cleared, and structured compilation of all evidence when submitting a claim.
Conclusion: Extending construction time requires evidence, not assumptions.
An extension of the construction period is not a gut feeling, but the result of verifiable and clear evidence. The decisive factors are a clearly identified cause of the obstruction, timely notification in accordance with VOB/B, the causal influence on the critical path and a realistic calculation of the extension of the deadline, taking into account restart and seasonal effects.
