Additional costs for residential units

What can I do myself in terms of planning to design multiple residential units as cost-efficiently as possible?

It is best to hire an architect who has experience with this type of house. The draftsman of a general contractor is unsuitable for this.

Bathroom over bathroom, kitchen over kitchen saves costs and simplifies planning.

Connections partly run through empty conduits.
Insulation, windows, dormers for hätte vielleicht evtl are expensive.

Parking spaces usually 2 per residential unit not one behind the other
Are 3 residential units allowed
What do the floor area ratio and the plot ratio say?

Bathroom after bathroom, kitchen after kitchen saves costs and makes planning easier.

All right, thank you very much, I can already take that into account in the rough planning.

Insulation, windows, dormers might maybe possibly be expensive.

Insulation will certainly be an expensive factor (for 40 plus). I have planned the windows so far as an architect once recommended to me for a passive house (more windows on the south and west sides with blinds to let in heat in a controlled way, few on the other sides). The architect will surely make changes here, but I am only planning a draft first so that he has something to work with. Dormers or fancy stuff on the exterior walls are not planned. Square floor plan, a pyramid roof on top.

Parking spaces usually 2 per residential unit not in a row

That would really be very intense. Yesterday, in a quick search, I found numbers more like 0.6 to 0.8 per residential unit. But since it strongly depends on the municipalities, that will definitely be an important point to clarify.

What do the floor area ratio and plot ratio say?

Floor area ratio 0.4, plot ratio 1.0. Both should not be a problem.

Best to take an architect who has experience with this type of house. The draftsman of a general contractor is unsuitable for this.

Definitely! I think I have a good one with a lot of experience who has also built multi-family and multi-generational houses. He also has experience with 40plus (which was harder to find than expected), so I am confident. I have a question about the roof, although basically off-topic. If this shouldn't be discussed here, I can gladly start a new thread for it. Insulating a roof is said to be significantly more expensive than a simple ceiling. Do you have a rule of thumb for how much more expensive the insulation makes it? And could I reasonably avoid that if I hang another ceiling in the attic (e.g. at 2.4m) so that I don’t have to insulate up to the peak of the pyramid roof? Then there would be an uninhabited cavity above, which should also help with the insulation, as far as I have read.

Square floor plan, on top a hip roof.

From a perspective point of view, a third residential unit is also to be created (attic). I would initially want to leave the attic unit in shell condition, but already have all connections, pipes, etc. installed.

Insulating a roof is said to be significantly more expensive than a simple ceiling.
Do you have a rough estimate of how much more expensive the insulation would be?

A hip roof contradicts having an attic.
With a hip roof, you build a three-story building; the hip roof is then constructed as a cold roof, so you can't have a living space in there.

Above all, how is that supposed to work with the staircase? Wasn't there something like the obligation of exclusivity?

Pyramid roof contradicts the attic.

Is that so? I have currently planned it optionally with a 30-35 degree pitch. This still results in considerable living space when converted, which would then suffice for an apartment for the child (especially in the first approx. 5-10 years during/after training/studies).

With a pyramid roof, you build a three-story building, the pyramid roof is then built as a cold roof, you also can't get a habitable room in there.

Is "cold roof" the correct term for what I previously meant by "hollow space for insulation"?
That would be my question: is something like that strictly necessary? Would it help to limit the ceiling in the pyramid roof to 2.4 m so that the peak would still be a "cold roof"?
Or is it basically the same cost-wise whether you insert the additional ceiling in the attic or insulate the roof all the way up to the peak?

Above all, how is that supposed to work with the stairwell?

The stairwell is designed so that each residential unit can be entered through a lockable door. Why should there be a problem in the attic? There, too, the stairs then end at a lockable door.