Basement or ground slab: which is more sensible for the property situation?

Thank you very much for the further contributions and variant discussions ( ), I will have various options from earthworks companies offered to get a feel for the costs. I assume that for a serious statement, in addition to the survey plan, a geotechnical report is also required...

I am in talks with a prefabricated house supplier, where the base slab etc. is included in the fixed price. The site-specific works (GSA) are of course not included, but a geotechnical report is needed to be able to calculate these. I have now inquired which information etc. a report must contain so that it can be used by the supplier and how high the credit would be in the event of a possible contract conclusion. In return, I have been offered to have the geotechnical report prepared in advance (costs borne by me, €1500, deduction from contract sum upon commissioning). After the evaluation, a fixed price offer for the GSA would be created. Would that be a feasible approach or should I rather commission individually and independently?

The ridge directions are marked in the garage annex. Are these mandatory? At least the neighbors have adhered to them.

No, there are almost complete freedoms regarding orientation and roof shape (see attachment)

In my opinion, the garage can comply with the development plan in this way. The house as high as necessary so that the slope towards the street works. I have already written that.

I now understand why this building form should also be possible. I had not thought of this idea so far. Can such questions be clarified in advance (e.g. call to the building authority etc.)?

You can still plan to place the front door on the side with a slightly recessed front:

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Then you have to excavate 20 cm more at the front, but need to fill less at the back and the adjustment to the terrain is even smaller. If it were mine, I would probably go even lower at the street front to overcome my garden exit at the back with few steps. But with these variants, the heavy rain issue must be specifically planned and of course the sealing against the soil.

Is the planning regarding heavy rain handled by the commissioned architect (or if a prefabricated house builder is commissioned, by them)?

This may sound a bit strange now, but you are always the one responsible first for something. It is your soil survey and you are buying it for your land. The soil survey also has relatively little to do with the executing company. You need to know what kind of soil it is, how load-bearing and permeable it is, whether there are rocks, etc.
If someone offers you a charge for it, that is in my opinion just an attempt to get you locked into the contract.

In my opinion, the planning of drainage is the architect's task. But even here: it is your project. If he forgets it, you have a problem, not so much him.

Depending on how much time people at the office have, you can of course ask questions before the construction. It is advisable to be very specific. With us, you can submit a preliminary request online. This is free of charge. Since we are a small community, I can also directly approach our head of office. Your architect can (hopefully) answer all of this as well. Btw. [Fertighaus am Hang] - that would not be my first choice.

Thank you for the explanations. That means under the given circumstances you would classically work with an architect (service phases 1-4) and then continue with the architect or general contractor (service phases 5-9)?

I am in talks with a prefabricated house provider,

Prefabricated house provider because of the popular misconception that they are the first choice for more accurate final price predictions?

where the base slab etc. is included in the fixed price.

The base slab should be seriously included in the offer precisely because it belongs in the scope of services of the (shell construction) general contractor. Without the base slab everything is nothing; it is literally THE foundation. Moreover, the upper edge of the concrete slab is also the root of all critical interfaces.

They offered me in return to have the soil survey carried out in advance (costs borne by me, 1500 €, deducted from the contract sum if commissioned). After evaluation, a fixed price offer for the general contractor would be prepared. Would that be a viable approach or should I rather commission individually and independently?

This is an intelligence test to check your ability to think beyond the obvious, with a bit of lubricant added for safety.
Your plot is the same with every contractor. Always commission the survey yourself. I already deliberately advised you to do a broad screening of the entire building window (and close enough to the corners to also capture homogeneity), because making a new one for each specific house footprint ("I take that back!") is nonsense.

So you would under the given conditions build classically with an architect (service phases 1-4) and then continue with an architect or general contractor (service phases 5-9)?

Although the question was not directed at me, I gladly give (and already gave in "A house-building schedule, also for you: the HOAI phase model!") the generally valid answers: always a freely chosen independent architect, NEVER!!!! service phases 1-4, service phase 9 is also complete nonsense for owner-occupied single-family houses, but:
1. Service phases 1 and 2 (called "Module A" in the house-building schedule)
2. Dough resting (normally with a setting of the direction, here I would omit all the wood constructors though, so just ask about 3 or 4 masons)
3. Service phases 3 to 8 (= Modules B and C) preferably with the same architect (note: 3 + 5 = 8).
And general contractor again my eternal litany "basically gladly, but not without a proper tender process anyway". The homeowner mistake of concluding from the balanced scorecard that one can safely commission them as a black box is an expensive national pastime.

So you would typically build under these conditions with an architect (service phases 1-4) and then continue with an architect or general contractor (service phases 5-9)?

The question should rather be, what would I recommend for you? I'm clearly on ’s side. On a slope, I would generally advise against prefabricated house providers. They only place their hut on the finished foundation slab without considering all the other issues of your slope. A general contractor (GC) is already better because there are definitely willing and committed professionals. If they are local, they have probably already built one of those "slope huts," which I would first inquire about, including references, as a prerequisite. Planning the outdoor area is usually no problem for a GC. As long as everything is paid for, everything is included, and you can put together a nice package. Most likely, I would advise you to go with an architect on the slope. The good thing about one is the focus on planning. A GC often only delivers mediocrity because they often only employ draftsmen. If it were mine, I would definitely start with an architect and go up to phase 2. Here I would first see if the matter has a chance. If so, I would continue with him up to phase 5. Since I already have quite a bit of experience and already have various trades more or less permanently in use with us, my approach from here is certainly different than yours. We would leave some things to the architect but take over most trades ourselves from then on. However, I cannot recommend this at all for "first-time home builders" and therefore strongly advise to continue with the professional. You can also mix both and, for example, continue with the GC after phase 2. But everyone has to find that out for themselves.