Floor plan design for KfW 40 single-family house in a developed residential area with fully finished basement

Number of floors: 2 full floors required

How large is the atrium supposed to be?

By the way, something is wrong with the file formats of your drawings, they try to download immediately but are then unreadable.

Infinite Monkey is very popular among the "Architect Generation CAD" and their clients, but in my opinion not a recommendable design methodology; I prefer a preliminary design (only after the translation of the room program into a building volume has been conceptually "computationally tuned" is anything drawn at all) as a Clean Code basis. Starting directly in the design phase is basically like "starting off in third gear" and regularly produces such capers as partially or completely omitted originally essential elements. To me, this looks like the work of a discount architect (service phases 1 to 3).
By the way, something is wrong with the file formats of your drawings, they try to download immediately but then are not readable.


Really seriously with a circle around it?

I haven’t calculated the area separately now but that is already many square meters and I wonder if the costs will then match that.

1.5 meters on such a small plot are in my opinion still quite considerable, which in turn will increase costs for the outdoor facilities. Have you considered that?
As with every one of these designs, I ask myself about the necessity of an expensive basement, since you, as you write, want to place it on an almost flat site. The intended use here has been discussed thousands of times and just by the monster size of 23.5 sqm for the technical room and separate basement playroom or the later use by the children, opinions differ greatly.
At first glance, I could well imagine your need, also with regard to the mentioned budget, in a house without a basement. In the floor plan, in my opinion, square meters are thrown around just like that and in the end, rooms result that are large but difficult to furnish.
Please enter your real furniture with measurements each and then you will already see some sticking points. Surely you don’t want to furnish the living room as drawn.
Who made the cost estimate?
I would not like the endlessly long hallway at all.
The "T" in the bathroom is always popular and again rather disturbing here.
I don’t know if it’s only due to the missing real furniture but it seems to me as if a standard floor plan was simply a bit extended each time to make it bigger but without an obvious advantage for living comfort.
The island is more of a small island and the currently also popular pantry behind the kitchen cannot come from a thinking architect. Put furniture in with real dimensions and you will see.
Start with real furnishing in order to see how it works!

Regarding the floor plan itself. The classic layout usually works. However, I find the cloakroom niche for 4 people too small. The hallway would be too narrow for me. I would convey something with the openness of the open living area. In the upper floor, you can do without the hallway nook and could still equip the children's rooms with doors. If you absolutely want to build a basement in the slope, then you have to reduce the floor area due to the budget, but it should work. I would then plan the children's floor on the upper floor, the parents in the basement. Then on the upper floor another small bedroom (guest, hobby), which can initially serve as a parent's bedroom while the children are still small. The bathroom can be bigger. The T is a space eater here. Regarding the toilets in the Ts, it should be mentioned that you cannot easily take care of a toddler with stomach flu or on other days. Keep in mind that the row house line in your south has the courtyard driveway.