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

Hello everyone,
I am new to the forum and have purchased a plot of land from the municipality in a new development area, which is to be built on with a single-family house in the next 1.5 years (1.5 or 2 stories).
However, I have been stuck for some time on the issue of the plot conditions (slight slope and below street level) and the associated question of whether a basement in the present situation might after all be the smarter/more cost-effective (or at least cost-neutral) solution. To answer this question comprehensively, offers from civil engineers and especially a soil survey are probably necessary. However, on the subject of the soil survey, I am going around in circles because all soil surveyors want as exact specifications as possible regarding the planned construction, which in turn depends on the decision about a basement or slab foundation.

I am hoping for advice on the following questions:

[*
Can the excavation from building with a basement be used to fill up the plot to street level (no chargeable disposal)?
[*]What advice can you give me regarding the soil survey (exact later construction not yet fixed)?
[*]I am wavering between the following scenarios (which do you consider more sensible?):
[LIST=1]
[*]Basement and filling the plot to street level with excavation (catch the northeast plot boundary with 1 m high L-shaped concrete blocks), allowing partial slope to the northeast to create a basement room with daylight that could possibly be used as an office. The technical room would of course also be in the basement, but I would like to avoid a lifting station if possible!?
[*]Filling the plot (up to street level or slightly below) and building with a slab foundation (catch the northeast plot boundary with 1 m high L-shaped concrete blocks). However, I am concerned about the costs of the fill material and the necessary compaction. Technical room on the ground or upper floor, no lifting station, but probably a backwater valve.

All prefab house providers etc. I have been in contact with so far have really not responded to these conditions, ask for a budget frame, and then assume a flat rate of €25,000 for the earthworks etc. I suspect that will not be enough and I want to make these costs tangible for financial planning! When the subject of a basement is raised, even architects generally say a basement is always expensive. If the budget is tight, forego the basement...

I don’t want to withhold the following information and premises from you:

[*]The plot lies below street level. The adjacent neighboring plot (southeast) was filled up to street level (OK RF EG +156.14 m).
[*]Due to the filling to street level, a backwater valve could be dispensed with. On the opposite plot (northwest, behind the sidewalk), it was not filled as high, so a backwater valve had to be installed there. With construction including a basement, even with filling to street level, I would probably have to calculate on a lifting station.
[*]According to the development plan, a retaining wall of up to one meter high may be built to catch the slope; beyond that, slope angles of 30 ° must be observed (see attachment). Of course, both neighboring plots have made use of this and have set corresponding L-shaped blocks on the northeast side.
[*]Basically, I would not necessarily have filled in, but since the plot was raised on the southeast side to this extent and the main light naturally comes from there, I almost see myself forced to at least partially fill in.
[*]Deviating from the neighboring development, I am considering placing the house (gable roof) with the gable perpendicular to the street (see sketch). The plot would then be better lit and more usable.
[*]Northeast, there is a castle at some distance which should also be considered in the planning of the house (view connection).
[*]The plot is 464 m² and located 800 m from a watercourse (approx. 15 m above the water surface, no flooding risk). Additional sealing measures on a basement are assumed (probably even a “white tub” [waterproof concrete box]). A neighbor who built with a basement had to seal from the outside (probably afterwards).
[*]The development plan is generally quite generous: 2 full stories allowed, THmax = 6.5 m, FHmax = 10.5 m, floor area ratio: 0.4
[*]Surveying is available (see attachment)

Thank you very much and I look forward to suggestions and advice!

Note: Your wish for anonymity is okay. Otherwise, good help is often only possible if all the facts are known. Your contribution is somewhere in between. Veiled street names, but still findable if you can use search engines. Maybe you can bring yourself to name the B-Plan here. (I won’t.)

Regarding the decision yes/no to a basement, I can’t contribute anything professionally substantiated. I would prefer to build with a basement, but sometimes that simply isn’t within the budget.

Best regards

PS: Burgblick – I’m a bit jealous.

At first glance, I would estimate that you can still build well without a basement. The terrain modeling will not be avoidable for you anyway. But the basement is then quite an additional expense. The question that one should actually ask first would be in my opinion: What do you need and what is the budget? Apart from that, a lifting station is not a catastrophe. If you still fear it, no one forces you to build one even with a basement. If I interpret your sketch correctly, you place your house at most on a slope. Maybe a squarer shape would be a bit cheaper.

More gladly tomorrow. For now, in short: with "(11ant) Kellerregel" / "Keller-Frage" you will find here my contributions on the subject of your property's opinion on basement yes or no or possibly partial basement. Whether the excavation is suitable for backfilling depends on its quality. In any case, it is dug up fluffier than in the previously installed state, so it requires compaction. When backfilled, it therefore does not have the same volume as when removed.

On the subject of soil reports, however, I go around in circles because all soil surveyors want as exact specifications as possible regarding the planned construction, which, however, also depends on the decision of basement or .

That is nonsense. The property and certainly the building area are not so huge that it would result in a multitude of sampling points. I would simply select the inner circle of the building area here.

Basically, with the slope you have the problem that you are caught between two stools. It is too much slope for a purely flatland plan, too little for a hillside house. When considering, you should always also take into account the complete outdoor facilities. Where will the terrace be located, how do you want to get from the house to the garden (stairs?), where would the light well of the basement office be? What is more sensible also depends somewhat on your requirements (e.g., how often do you use the office?). Ultimately, two very different floor plans emerge here in two variants. That is why I only want to address one detailed question

Kann bei einem Bau mit Keller der Aushub zur Auffüllung des Grundstückes bis auf Straßenniveau verwendet werden (keine kostenpflichtige Entsorgung)?

Excavated material can of course be used for embankments, but most soils cannot be compacted in a controlled manner and you have to reckon with settlements. You can create lawns and flowerbeds there, but you must base a driveway on gravel.

Basically, with that slope you have the problem that you are sitting on the fence. For a purely flatland plan, it is too steep; for a hillside house, it is too little.

Which brings us to split-level as another option. It doesn't have to be half a floor right away. Sometimes just 2 to 3 steps on the ground floor are enough to achieve a noticeable effect. This also often allows for very nice zoning.