Single-family house Bauhaus style living area 180m with double garage

Hello everyone,

after a long time of (silent) reading, here comes my first post – I just need your opinion / advice now – Warning: This will be a wide-ranging attack, the number of questions just doesn’t get any smaller.
We (my wife, me, and one child – prospectively we wish for another child) are going to buy a plot of land from a municipality in South Baden (notary appointment on 14.08.).
The plot is 530m² and very "free" in terms of development, i.e. roof shapes etc. are very open.

So now we come to our idea:
- We want a single-family house (Bauhaus style) with a living area of 180m² (don’t ask me why we want exactly 180m² living space (more on that in open questions) – so far it was just a number, but it is becoming more and more solid…), no golden faucets, smart home if at all only basic, a tiled stove, 2 children's rooms, ... possibly ventilation system, heat pump,... How much living space do I actually need? We don’t really get any wiser through our research…
- Furthermore, we want a basement mainly for storage & building services – further development into a hobby room / office prospectively conceivable, but not at the beginning
- A double garage (alternatively single garage and a carport) round off the "hard facts"
- Energy efficiency: Good question – we would like to do “something”, but that something is “towards” KFW 55 and not KfW40 plus
- About the budget: We always hovered around the magical number of half a million, but reality caught up with us, so we adjusted our budget, it looks as follows: - The plot costs us 150,000 EUR, current estimates (+-15% deviation, but the architects have credibly assured us that this is a conservative estimate and rather represents the upper edge) from the architects are between 550,000 EUR and 650,000 EUR (without own services but including all ancillary services), so we adjusted our maximum budget for the entire project to 800,000 EUR, consisting of the land, the house including ancillary services as well as 50,000 EUR for kitchen etc. => 800,000 EUR.
- Own services we plan, if at all, the "usual" such as floors and possibly painting work as well as the garden
- Through my father’s network, we know one or the other craftsman with whom he worked in his old company (self-employed in the field of gardening & landscaping). Therefore, for example, we get the excavation work done cheaply by the construction group, etc.
- We had contact with a large and well-known prefabricated house manufacturer – based on wood – for quite some time but after seeing the price, we decided against it (Note: We once lived in an apartment in a house made of timber frame construction, that was a horror and we were therefore somewhat biased regarding the subject of wood)
- So far we have been in contact with four architects, one was dropped on price (about 20% more expensive than the other two) and another did not convince us => So two remain. (After we reduced the shortlist to two, we were recommended another architect with whom we had coffee, but he was so chaotic, so disorganized and the office completely messy that we did not even speak "intensively" with him.)
- With the two architects in closer selection, we have now agreed to get in touch early next week and share our decision.
- At the same time, the Association of Private Builders (Verband Privater Bauherren) pointed out in their welcome email that the cost estimate with the model with architect and awarding of individual trades "may be exceeded by 30 to 40%".
- Now we are somewhat confused because we respect the price framework and the possible deviation of +15% on 600,000/650,000 EUR (thus between 90,000 EUR -100,000 EUR, simply not a small amount)

How do you see the whole thing? Is the cost estimate (details below) realistic? Realistically overestimated? Should we perhaps consider a general contractor after all? Do you know any? (Is it even allowed to mention names here?)

As mentioned above, here is the rough cost estimate we received from our architect number 1:

*: All prices without tax

a) Building – Building constructions: 371,500

[*]Shell construction: 170,000
[*]Carpentry work, roof construction: 65,000
[*]Scaffolding: 5,000
[*]Interior & exterior plastering: 30,000
[*]Tiling work: 13,000
[*]Screed: 8,500
[*]Interior doors: 5,000
[*]Metalwork: 7,000
[*]Window construction work: 40,000
[*]Painting work: 8,000
[*]Floor covering work: 5,000
[*]Dry construction: 15,000

b) Building – Technical installations: 100,000

- Heating: 26,000

- Sanitary: 25,000

- Ventilation system: 14,000

- Electrical: 30,000

- Sewage lifting pump: 5,000

c) Additional building costs: 79,000

- Architect including drainage: 55,000 (for 60,000 gross, including tax we could provisionally agree)

- Structural engineer: 7,500

- Energy consultant: 1,200

- Surveyor: 1,500

- Soil report: 1,000

- Permit fees: 3,800

- Sewer connection development: 200

- Power connection, telecom connection, cable connection, water connection: 4,500

- Construction power: 1,300

- Other additional building costs / fees: 2,000

Thus, we come to around 550,000 net +19% => 655,000 EUR

What do you think? Is that justified? Is it overplanned? Conservative? Too expensive?

Should we rather go with a general contractor to have "planning security"?

Thanks in advance for reading and your advice.

That's fine. But for the house, you have to calculate at least 600,000 to 650,000.

All the mentioned trades would be cheaper here. But you are in southern Germany, so everything costs a bit more.

In my opinion, the shell construction is quite high. What is included? Monolithic, basement, garage, including earthworks? Electrical 30k€ for conventional electrics is also rather a lot. 40k€ for windows is not little either, I assume including the front door and a bit more glass with blinds? Ancillary costs look good, only the house connections I find too optimistic, I would rather estimate 10-12k€ including wastewater (the 200 is a joke?! Just the transfer shafts alone cost 2k and up).

So I find it quite fitting. But diagnosis from afar is of course difficult.

How much living space do I actually need?

130-170... that would be a rough number. But I tend to around 160. More can’t hurt if you can afford it.

Furthermore, we want a basement mainly for storage & house technology –

Then you only need 130-140.

Make a room plan, a room concept. You need about 5-6 sqm for house technology. Storage should be where you need it: laundry room on the upper floor, storage and pantry on the ground floor... for that you don’t need a basement.
Ps: the office is already included in the 160.

Two architects to choose from should be enough, although I also have good experiences with chaotic types and would give more weight to client references than to how the office of the absent-minded professor looks. 180 sqm is definitely not a size for poor people, and especially in the "Bauhaus style" some modernity is expected, i.e. with regard to resale value, I would not keep the smartness of the equipment too low.

Is the double garage including the roof already part of the shell construction as well as the basement? Stairs and carpentry must also be considered. Don’t forget shading, paving, furniture, interior window sills. 7500 for the structural engineer seems very high to me; the construction must be very complex for that.