The question I keep asking myself: Is this now a free market or how do such fluctuations come about?
In HOAI 2013 there is an annex 10 that lists the basic services in the service profile "Interiors and Buildings". It finally lists what the individual service phases include.
In addition, there are so-called "partial service tables" (e.g. from Siemon), which in turn assign the proportional fee of each service phase to these basic services.
Example:
Billable costs (=/= construction sum!) = €300,000, fee zone III, middle rate
For service phase 2 (preliminary planning) 7% of the total fee are due, therefore €3,144.57
Service phase 2 includes the following basic services, to which Siemon assigns the following shares:
a) Analyzing the basics, coordinating the services with the parties professionally involved in the planning
--> 0.25% to 0.50%
b) Coordinating the target objectives, pointing out target conflicts (included in a)
c) Developing the preliminary planning, investigating, presenting and evaluating variants according to the same requirements, drawings to scale according to the type and size of the object
--> 3.00% to 3.50%
d) Clarifying and explaining the essential contexts, specifications and conditions (e.g. urban planning, design, functional, technical, economic, ecological, building physics, energy management, social, public law)
--> 1.00% to 2.00%
e) Providing the work results as a basis for the other parties professionally involved in the planning as well as coordination and integration of their services (included in d)
f) Preliminary negotiations about the approval
--> 0.10% to 0.50%
g) Cost estimation according to DIN 276, comparison with the financial framework conditions
--> 0.75% to 1.50%
h) Creating a schedule with the essential processes of the planning and construction sequence
--> 0.10% to 0.50%
i) Summarizing, explaining and documenting the results
--> 0.10% to 0.50%
Now the architect can go ahead and cut service phase 2 by basic services that he considers dispensable for the specific project. For example, point f) would probably only rarely be an obligatory part of his services. He deducts 0.5% of the total fee for this and his offer will then be €224.61 cheaper.
In this way it is of course also possible to fall below the minimum rates of HOAI (according to service phases), but this requires explicit agreement and should be stated in the contract.
In my humble experience, however, it usually works more like this: the architect simply sticks to his routine and makes sure that his working time ultimately fits the fee. Single-family houses are simply fillers between the lucrative projects.
I have written this somewhere here before; the nonsense known from relevant shows (e.g. BR "Dream Houses"), where the architect is passionate about the matter, designs x totally creative variants, lovingly builds small models, brings samples of numerous materials, advises the client while choosing finishes and finally proudly puts the construction on the landing page, you will not find in reality. These are either the architects’ own projects, or it is about construction sums beyond all sense at which the architect actually earns really well.
Honestly: If I absolutely needed an architect, but could not really afford the actually necessary €35,000 upwards, I would take the cheapest one and lower my expectations to zero, then everyone will be satisfied in the end.
PS: A quick note on the "billable costs". HOAI writes about this:
§33 Special basis of the fee
(1) For basic services for buildings and interiors, the costs of the building construction are billable.
(2) For basic services for buildings and interiors, the costs for technical installations, which the contractor does not plan professionally or does not supervise professionally in their execution,
1. are fully billable up to an amount of 25 percent of the other billable costs, and
2. are billable at half the amount that exceeds 25 percent of the other billable costs.
(3) Costs for site preparation, for non-public development, as well as for services for equipment and works of art are not billable, especially if the contractor neither plans these services nor participates in procurement or professionally supervises their execution or installation.
If the construction sum is €350,000 and of that €100,000 accounts for the "technical building equipment" (heating, electricity, controlled residential ventilation, etc.), the calculation would be as follows:
€350,000 gross corresponds to €294,000 net. Of that €84,000 net for the TGA. Results in billable costs of
210,000 + 52,500 + 15,750 = €278,250 billable costs