Two-family house, optimize?

3. the granny flat, we want to rent it out or later swap it in old age

The question was more about the motivation for this consideration... WHY do you want to rent it out? Because the financing is supposed to be paid with it? You should seriously reconsider that because it is usually not worthwhile.

2. spatial understanding, where is the problem?

... that you do not see certain things. The , whom you criticized, rightly put the finger on the wound, so respond to the concrete points if you want help here...

There is also an 18-year-old child who will soon finish training and wants their own apartment. Besides that, there are hardly any apartments and almost no houses for rent in our town.

I am by no means a professional, but probably somewhat more practiced than you.

You should be able to read the floor area ratio/site coverage ratio from your development plan; they indicate the extent of the construction. You cannot arbitrarily build over much of your property; there are usually regulations. A floor area ratio of 0.3 means: only 30% of the available area may be built on. Explained very roughly – there are also details like terraces, driveways, outbuildings, and how they are assessed. Educate yourself on that! If there is no development plan, usually §34, insertion requirement, applies. That means, explained very roughly: you have to build like the neighbors. Not in style, but in the type of construction. If all around there are farmsteads with large plots and little built-up area, you will not get approval for a floor area ratio of 0.8. The site coverage ratio is then the floor area ratio and tells you how much upper floor is permitted or what kind of knee wall you have to build. As a non-professional, I’m not in the mood to explain this in more detail now. You can easily find this on Google and read it explicitly. Every non-professional can manage that.

For an 18-year-old child, no separate apartment is needed; a separate living area is sufficient at first. Will the child always stay in the area? What if the job in the next larger city is more interesting, exciting, and better paid, and the child wants to move to the city? Should strangers then move into the house, meaning should the separate apartment be rented out? And if I see the age correctly, the child is not included in the list of the three children living in the house, right? Now plan for old age. Unfortunately, no information on how old you are. But if you are not already near retirement age, it is rather unlikely that you will stay in that huge house when all four children have left. And if you do, you can remodel after 20 or more years. I wouldn’t limit myself for that now.

But these are very basic considerations you should think about. The design is simply just bad, I’m sorry. There are people here (for example Kaho) who as non-professionals bring good designs, they have a knack and a feel for it. Others don’t. It requires a lot of experience. You will meet people here who have been hanging around this forum for years. Because it’s fun (to me too!) to deal with floor plans. You see a lot. And very often enthusiastically presented designs by people who might be great cooks but should rather leave the floor plan to someone who can do it. There are also people who burn water, I wouldn’t go to eat at their place either… There are also people who have a flair for designs. We also see quite good amateur designs and bad architect designs. Or lousy designs from a general contractor who tries to adapt his standard design to the client’s needs with as few changes as possible and makes it worse. We have all of that here.

Only: if you ask for feedback here, then take it. For this design you will hardly get good feedback. I say this as a non-professional but an experienced forum member.

And by the way: nobody here deals with standard designs. At least I don’t know anyone here who waves little flags around *lol*

Size of the plot 750 m² South slope approx. 25% Site coverage ratio Floor area ratio Building window, building line and boundary B 21m x D 14m

Where is the slope considered in your design? Site plan missing.

This is what a development plan looks like. In this case (is from Forchtenberg), for example, a floor area ratio of 0.4 is specified ==> so 40% of the property may be built upon (including driveway, terraces, garages, etc., although there may be other calculation variants there). You will also find statements there regarding the number of floors, ridge heights, and other points. If you want to build two stories, you must also be allowed to do so.

I gladly accept and take the feedback. After looking at the plan again with the note about the buildable area, I have to admit that the plan is rubbish.

Regarding the granny flat and the 18-year-old, it is the wish and decision of the person involved, and reasons have already been given why it should/must be a granny flat.