Planning tasks change. That is not the exception — it is the rule. A revised structural requirement, a new variant in the fire protection concept, an additional coordination round with the client: services that were not originally commissioned arise in almost every live project. The real question is what happens next.
In many engineering firms, what happens is this: the additional work is carried out, perhaps noted internally, but rarely consistently formulated as a supplementary claim, assessed, and enforced against the client. At the end of the project the proof is missing, the discussion begins, and part of the work delivered remains unpaid.
This is not an isolated case. According to a survey by the Federal Association of Engineering Chambers, unclear service boundaries and missing supplementary claims documentation are among the most common economic risks in the planning business. The cause is rarely poor work — it is missing processes.
Key points: Where supplementary claims management has an impact at project level
- Scope changes often arise verbally or by email without being classified as a service change
- Additional work is often carried out before a commission has been issued
- Missing time documentation makes it difficult to provide proof to the client
- Without systematic recording, the foundation for a legally secure supplementary claim invoice is absent
- Unbilled supplementary claims directly and permanently burden the project margin
What a Supplementary Claim Means in Planning Law
In engineering law, a supplementary claim is a change or extension of services relative to the original contract. The legal basis, depending on the contract structure, derives from Section 650b of the German Civil Code (BGB) (the client's right to issue instructions) and, in the case of public clients, from the VOB/B and the HOAI provisions on fee adjustment for changed scope of services.
When Does a Supplementary Claim Arise?
A supplementary claim arises whenever services are rendered outside the contractually agreed service profile. These include:
- Additional variant studies not included in the schedule of services
- Extended coordination services due to changes in project participants
- Design changes resulting from subsequent client requests or regulatory requirements
- Repeat services triggered by the client's design changes
- Additional services in fire protection, building services engineering, or structural engineering due to changed normative requirements
What HOAI and BGB Say About This
Under Section 10 of the HOAI, additional services not included in the standard services of a service profile can be remunerated as Special Services. The prerequisite: they were agreed. Without written commissioning, or at least provable commissioning, things become difficult.
The German Federal Court of Justice (BGH) has clarified in several decisions that there is in principle a right to remuneration for supplementary claims when the client ordered the service or the contractor was entitled to consider it necessary to fulfil the contract. What is decisive is the proof.
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Where Supplementary Claims Management Fails in Practice
Problem 1: Changes Are Commissioned Verbally
In day-to-day project work, many decisions happen by phone, in meetings, or via informal emails. The engineer notes internally that the structural concept needs to be revised again. The client decided this in a meeting. It is rarely documented.
Without a structured record of these commissioning moments, the basis for a supplementary claim is missing later on. What was not recorded in writing does not contractually exist.
Problem 2: Hourly Expenditures Are Not Assigned at Project Level
Even if an engineering firm knows that additional work has arisen, without reliable time recording at service level it is impossible to show how much effort was actually incurred. If project time tracking only works at project level but does not allow assignment to service phases, trades, or tasks, the time record for a supplementary claim invoice cannot be produced.
This is a structural problem. In planning firms that work with Excel, this level of granularity is almost always absent.
Problem 3: No Clear Responsibility for the Supplementary Claims Process
Who creates the supplementary claim? Who follows it up? In many firms this falls implicitly to the project manager, who simultaneously has to deliver, coordinate, and steer. Supplementary claims slip to the back until the project is almost complete and the client has no more motivation to acknowledge additional costs.
Late-submitted supplementary claims have a significantly lower enforcement rate because the causal link between the service change and the additional work is harder to establish.
Problem 4: Missing Valuation Basis
Even if the additional work was recorded: at what hourly rate? According to which service profile? Without a stored rate and calculation logic in the project, every supplementary claim invoice triggers a fresh discussion about the valuation basis.
Setting Up Supplementary Claims Management in a Structured Way: From Recording to Billing
Step 1: Classify Scope Changes Immediately
Every deviation from the original scope of services should be assessed immediately as a potential supplementary claims situation. Concretely: meeting minutes are flagged with a change note, emails instructing service adjustments are marked as such, and it is recorded internally which service is to be rendered and on what commissioning basis.
This awareness must be embedded at the level of all project participants — specialist planners, project managers, and the office management. If only the project leadership is tracking the issue, changes at other levels regularly go unnoticed.
Step 2: Record Hourly Expenditures at Service Level
For a supplementary claim invoice you need proof, not an estimate. This requires that project time tracking is set up at a granular enough level for hours to be assigned to a service phase, a trade, or a specific activity — and not just to the project as a whole.
An engineering firm that only books times at project level cannot show in a dispute how many hours were attributable to the revised structural design and how many to the original service. With structured recording at task level, this transparency arises automatically, entry by entry, throughout the entire project. ZEP Compact enables exactly this: project times are assigned to service phases and tasks, the actual effort is evaluable at any time, and the data foundation for a supplementary claim invoice is created during live operations — without retrospective reconstruction.
Step 3: Formulate and Communicate the Supplementary Claim Early
The ideal time for a supplementary claim is before the service is rendered. That is the ideal scenario. In practice it often falls shortly afterwards, once the actual additional work is visible.
What is decisive: do not wait until project completion. A supplementary claim submitted three months after the service has been rendered is rejected significantly more often than one submitted promptly. The documentation is fresher, the causal link clearer, and the client still has a memory of the decision-making situation.
Formulate the supplementary claim such that scope of services, commissioning basis, time record, and fee assessment are clearly presented. This protects you in a dispute and increases acceptance with the client.
Step 4: Track Supplementary Claim Status in the Project
A submitted supplementary claim is not a completed matter. It must be followed up: was it confirmed? Disputed? Is the client silent? Depending on the contract structure, silence has different legal consequences, which makes a structured follow-up system indispensable.
In project controlling, every open supplementary claim should be tracked as its own line item, with status, amount, and expected decision date. Only in this way can the economic position of a project be realistically assessed.
Step 5: Transfer the Supplementary Claim into Billing
Once the supplementary claim is acknowledged, it must flow into billing. This sounds obvious, but in many firms it is a manual step in which information is copied back and forth between project documentation, Excel, and the billing system.
Media breaks at this point are not only laborious — they also generate errors. Hourly rates are transferred incorrectly, items are forgotten, invoices have to be corrected. With project billing based on the same time data as the controlling, this step is eliminated.
When Supplementary Claims Become a Recurring Issue: Time to Ask the System Question
Individual supplementary claims can still be managed manually. But as soon as an engineering firm is running multiple projects in parallel — each with its own service changes, its own commissioning histories, and its own billing statuses — the issue becomes structural.
The questions that then arise are:
- Which supplementary claims are currently open across all projects?
- How much unbilled additional work is contained in the current project portfolio?
- When were supplementary claims submitted, confirmed, and billed?
- Which projects systematically show unresolved additional work?
These questions cannot be reliably answered with Excel, because Excel is not a living system that consolidates time data, project status, and billing status on a single data foundation.
ZEP Professional closes exactly this gap: from additional work through the supplementary claim to the invoice, everything runs on a single data foundation. Project times, task assignment, service records, and invoicing are integrated. What was delivered is also billed.
Conclusion: Supplementary Claims Management Is Project Margin Management
Supplementary claims that are not submitted are not an academic question. They are direct margin loss. An engineering firm that consistently bills additional services achieves higher economic output from the same resource deployment than one that does not.
The foundation for this is not a complex process but a cleanly configured system:
- Classify scope changes immediately — do not reconstruct them retrospectively
- Record times at service level, not just at project level
- Formulate supplementary claims promptly and track them as their own line item in controlling
- Base billing on the same data as the recording
If you find that additional work in your firm regularly arises but is rarely fully billed, that is the moment to rethink the process. Start with time tracking. Everything else builds on that.
FAQs
When do I as an engineer have a right to remuneration for an additional service?
A claim to remuneration arises when the service falls outside the originally commissioned scope and was either explicitly ordered or was necessarily required to fulfil the contract. What is decisive is the ability to prove the claim: anyone who can document the commissioning and the actual effort is in a significantly stronger position in the event of a dispute. Without proof, even a justified claim is difficult to enforce.
Does a supplementary claim have to be agreed in writing?
Written form is not strictly required under the German Civil Code (BGB) for a supplementary claim to be valid, but it is almost indispensable in the event of a dispute. Verbal commissions are legally possible in principle but difficult to prove. In practice, at a minimum a confirmation by email or a minute entry documenting the commissioning situation is recommended.
How do I calculate the fee basis for a supplementary claim under the HOAI?
If the additional service qualifies as a Special Service under the HOAI, the fee is governed by agreement between the parties, since the HOAI does not prescribe binding minimum rates for Special Services. Without an agreement, the customary market rate applies. It is important to base the calculation on comprehensible hourly expenditures and hourly rates that have been stored internally in advance.
What do I do if the client rejects a supplementary claim?
First, point out the claim in writing and request a justification for the rejection. If no agreement is reached, mediation, an expert determination, or legal proceedings are possible depending on the contractual situation. A complete set of documentation — commissioning proof, time records, and correspondence — is the most important basis in this case.
From what point should an engineering firm introduce a system for supplementary claims management?
As soon as multiple projects are running in parallel and scope changes are no longer the exception, a systematic approach pays off. In practice: firms with more than five to ten active projects simultaneously regularly lose supplementary claims volume without structured processes — volume they can no longer quantify. That is the point at which a manual approach becomes too expensive.
What data do I need for a legally secure supplementary claim invoice?
At least four elements: the commissioning basis (instruction, minutes, email), a description of the additional service rendered, a service-level time record with date and activity, and a fee assessment based on agreed or customary hourly rates. If any one of these components is missing, enforcement becomes significantly more difficult.
