Case one: changed scope
The provision attaches to two cumulative conditions. One alone does not suffice, and that is precisely where most claims fail.
| # | Condition |
|---|---|
| 1 | Client and consultant agree during the term of the contract that the scope of the commissioned service is changed |
| 2 | As a result, the chargeable costs, areas or accounting units change |
Where both are met, the fee basis for the basic services to be performed as a consequence of the changed scope must be adjusted by agreement in text form. The adjustment does not take effect by itself but has to be agreed.
The cumulation is the decisive point and is regularly overlooked. A change of scope alone does not trigger adjustment; it must affect the fee basis.
Case two: repeated basic services
The second case concerns the situation where the parties agree on the repetition of basic services without the chargeable costs, areas or accounting units changing as a result. It closes precisely the gap the first paragraph leaves open.
The fee for those basic services must then be agreed in text form according to their share within the relevant work phase. The share is therefore a matter for negotiation rather than a calculation result.
This is the fitting provision for a common situation: the client rejects a design and requires it to be reworked, without the building volume changing. The basic services of the developed design phase are performed a second time; chargeable costs stay the same.
Here the same difficulty arises as with partial commissions: the HOAI does not weight individual basic services. The share must be agreed, and in practice assessment tables from the professional literature are used. The system is covered in the article on partial commissions.
What the provision does not cover
Three situations fall outside its scope and must therefore be regulated separately. What they share is that effort arises with no basis for a claim in the regulation.
| Situation | Why it falls outside | Where the answer lies |
|---|---|---|
| Change without effect on the fee basis and without repetition | neither chargeable costs altered nor basic services repeated; example: greater coordination effort without physical consequences | the contract, e.g. hourly rates |
| Additional services | the service is not a basic service | rules on additional services |
| Cost increase without a change of scope | the commissioned scope stays the same | none; the cost calculation remains governing and the fee unchanged |
Timing governs
The provision speaks of agreement during the term of the contract and of adjustment by agreement in text form. Together these imply a practical sequence whose neglect is expensive.
| Sequence | The designer's position |
|---|---|
| Discuss the change, agree the adjustment, then perform | strong, the claim is settled |
| Discuss the change, perform, then seek adjustment | weak, the work already exists |
| Perform, then assert both change and adjustment | very weak, even agreement on the change is missing |
The second row is the norm in practice and the reason for most disputes of this kind. The client has no further interest in an agreement once the work has been performed.
The most effective countermeasure is a message in text form before implementation, containing three items: the change, its effect on the fee basis or on effort, and the adjustment proposed. It costs ten minutes and moves the negotiation into the period when both sides still have something to gain.
The commonest triggers in practice
Four situations produce most changes, and they fall differently under the provision. The distinction decides which of the two paragraphs applies at all.
| Trigger | Do chargeable costs change | Applicable provision |
|---|---|---|
| Increase in building volume | yes | adjustment of the fee basis |
| Higher specification standard | yes | adjustment of the fee basis |
| Rejected design requiring rework | no | remuneration of repeated basic services |
| Conditions attached to the consent | depending on extent | in doubt, to be regulated separately |
The fourth row is the hardest. Consent conditions force adaptations that neither constitute agreement on a change of scope nor necessarily alter chargeable costs. They therefore frequently fall outside both paragraphs.
That is why starting detailed design before consent is granted should be regulated contractually, as described in the article on work phases 4 and 5. Without such a clause the consultant carries the risk of a condition they did not cause.
What belongs in the contract
Since the provision is narrowly framed, a contractual supplement covering the uncovered cases is advisable. Four points suffice, and they fit on half a page.
| Point to regulate | What it covers |
|---|---|
| A change procedure | who notifies a change, how it is recorded, within what period the consultant quantifies the effort |
| Hourly rates for uncovered cases | changes that neither alter the fee basis nor constitute a repetition |
| The weighting basis for repeated services | which table is used to weight partial services |
| The treatment of delay | a longer construction period without a change of scope: the effort of site supervision grows, the fee basis does not; the HOAI does not regulate this case |
The last point is economically the most significant on long construction periods and is almost never addressed in contracts. Where the construction period doubles, the effort of site supervision doubles and the fee for it does not.
Related articles
This article reflects the position of the rules and case law at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.