Land planning for new single-family house 180 sqm, with space for a grand piano

Hello everyone,

I have always been a silent reader until now, but somehow I am not making progress with my plans.
Here are the basic details first:

Size of the plot	900 sqm (already available)
Slope	The entire plot slopes from north to south by approx. 1.2m over 29m, in the building window of the house over 13m it slopes approx. 0.6-0.8m
Site occupancy index	0.2
Floor area ratio	0.33
Building window, building line and boundary	House 15x11m, garage 6x8.5 (garage may be wider if it lies within the house’s building window) However, the building window was defined for a smaller plot. The plot was later extended slightly to the east, see image Baufenster.jpg. I assume that the building window may also be shifted accordingly to the east. Approval for this is still pending.
Edge development	garage only
Number of parking spaces	2
Number of floors	2 full floors
Roof type	Gable roof with 25-30 degrees
Orientation	View from living-dining room to the northwest as it is unobstructed here

Maximum heights/limits	- Wall height 6.1m (from top of ground floor) - Plinth height 0.3m (from top of ground floor) - Excavation not permitted - Backfilling up to 0.5m - The ratio of width to length must not deviate significantly from 1:1.2 - Excavations and backfilling are permitted for the garage driveway (plinth height up to 1m)
Basement, floors
Number of people, age	Currently 2+1 (+ space for a second child must be available)
Space requirements on the ground floor	Large entrance area with lots of storage, spacious living-dining room with pantry, guest room, guest bathroom
Space requirements on the upper floor	Bedroom with optional separate dressing room, bathroom, children’s room 1, home office. (If there is a basement, then the guest room will move to the basement so there is space for a second children’s room. If no basement, we need a second children’s room upstairs.)
Office	is needed (1x home office)
Overnight guests per year	Occasionally, for 1-2 days, about 5-10 people.
Open or closed architecture	Mixed. Staircase outside the living area, but an open space in the entrance area would be nice. Open living-dining area is nice for the feeling of space, but if it can optionally be closed off, that would also be advantageous.
Open kitchen, kitchen island	Open kitchen yes, kitchen island not necessary. We like U-shape because of short distances.
Number of dining seats	6+2 (dining table is 2.2x1 meters)
Music/stereo wall, TV wall	Should be on a wall and offer space for storage. We did not like an architect’s draft where the TV serves as a room divider to the dining area.
Balcony, roof terrace	If there is space in the bathroom for a sauna, a balcony would be nice. But probably it will be omitted for cost reasons.
Garage, carport:	For 2 cars. Garage would of course be better, but not a must. Possibly also a combination where the carport also serves as a roofed entrance to the house.
Special features	View to the southeast is not nice because of industrial facilities.

Client requirements
Bright with plenty of space, modern, open but not too stylish. Function follows design.
Lots of space and storage, no dark corridors, entrance area if possible with an open space.
Guest bathroom and staircase to the upper floor should not be directly at the front door (dirt area).
We have a grand piano (1.6x1.8m) that must fit in the house (heirloom with personality. It is played but only occasionally). Ideally in the living room on the ground floor in a dark corner to avoid direct sunlight. If necessary, upstairs. Definitely not in the basement.
Well insulated. We are considering pursuing a QNG certification to get the KFW loan. However, if this would only be possible with significant unreasonable extra effort, then not.

House design
Who created the design: -Do-it-Yourself

What do you particularly like?
The version with the straight staircase is basically just a larger version of a model house with a base area of 10x12, but I am not a fan of straight staircases and the access to the basement would be through the living room. On the other hand, I like the entrance area with the separate cloakroom.

With the bay window version: the bay window probably drives the price up a bit. Access to the guest bathroom here is through the dirt area of the front door. If I swap staircase and guest bathroom, the bathroom has no window. Unless I also push the garage further forward.

With the 10x12.5 version: The piano somehow doesn’t fit in.

Personal price limit for the house, basement, including equipment, garage, terrace, driveway
900k

Preferred heating technology:
Air heat pump with underfloor heating and ideally also with central residential ventilation.

If you have to do without, on which details/extensions
-can you do without:
The piano can move upstairs if necessary. The garage can be replaced by a carport.

-cannot do without:
The basement is still up for discussion. My wife is pro basement. I could do without it.

Why did the design turn out the way it is now?
Playing around with SweetHome 3D after studying many model houses and floor plans that all did not satisfy us because one room was always missing or there was not enough space in the living room for the piano.
The goal is to get an idea of how much living space is needed when all desired rooms are included to then make a cost calculation.

I always try to limit myself to 10x12 sqm so that the total living space does not get out of control.
But I always hit the limits of fitting in both a guest room and the piano on the ground floor. The whole thing should not feel cramped. I definitely do not want to go bigger because we don’t need the space upstairs.

I am open to any criticism. Mentally I am probably so fixated on the floor plans that a push in a completely different direction would not be bad.

Questions I ask myself:

[*]Will we manage with the budget of 900k to build the house + basement + garage + driveway + terrace and garden fence?
[*]Is a basement much more expensive? If I need a technical room, utility room, storage room, and a second children’s room instead of a basement, I also have high costs.
[*]Does it make sense to plan a guest room in the basement? We hope for a room in the southeast basement that gets some daylight, as the plot is lowest there and excavation is necessary anyway for the driveway to the garage.
[*]Can I accommodate my wishes on 10x12 sqm without the piano feeling too squeezed in?
[*]Is a standard house (or a free plan with a general contractor) sufficient for our idea, or should we urgently consult a freelance architect beforehand?
[*]Is the orientation of the house sensible or are there other suggestions? We are relatively restricted by the building window, but there are several houses in the building area that deviate considerably. And we want to apply anyway to shift the house eastwards after the plot was expanded there.
[*]Does it make sense to cellar the garage instead of the house? We don’t need a huge basement, but 50 sqm would be good.

Aerial photo attached. I was no longer able to attach it afterwards via the edit function.

Basic recommendation ... always align all site plans and floor plans uniformly.

Where is the [OG-Grundriss]?

With 900000€ AI you get a nice house on this plot with the restrictive specifications. 50000€ ancillary construction costs, 50000€ paving, 50000€ garden and garage, and about 50000€ for buffer. For 700000€ you can afford just under 200-220sqm of living space. Or less with a usable basement (at KfW40). Two children's rooms certainly fit upstairs next to a parent's unit - you can also manage that on a total of 140sqm as a single-story house with attic extension. What you apparently do wrong: you don’t manage or plan with the sqm, but simply apply a catalog grid to the 10x12, sketch it, and take that as your design. I’ll put it this way: with your budget, you can also afford an architect who gets the best out of the plot.

The goal is to get an idea of how much living space is needed if all the desired rooms are to be accommodated, in order to then make a cost calculation. I always try to limit myself to 10x12 sqm so that the total living area does not get out of control. But I always run up against the limits of accommodating both a guest room and the grand piano on the ground floor. The whole thing should not feel cramped. I definitely don’t want to go bigger because we don’t need the space upstairs.

Read your own words and realize: the grand piano will end up upstairs. But probably in one not self-designed. 120 sqm of floor area will result in about 190 sqm of living and usable space over two floors. The professional plans the upper floor first, by the way.

I am probably so stuck in my mind with the floor plans that a push in a completely different direction would not be wrong.

Then don’t deal with floor plans for several weeks.

Where is the upper floor plan?

Yes, valid question. I know that the upper floor is more important, but the decisive factor is whether the wing has to go into the upper floor or if there is space on the ground floor. And to answer the question, I first tried on the ground floor.