Development plan single-family house - regulations for new construction on shared property

Hello! We want to build another house on my mother's property next to my mother's existing house. Basically, a semi-detached house directly adjoining. The floor area ratio and floor space index would be sufficient. However, the development plan specifies the building type for the property as "only single-family house permitted" (open construction method). What legal regulations are there – is it, among other things, possible to have separate entrances and heating systems? Where can I find building law information about this?

The property cannot be divided due to the requirement "only single-family house permitted." Therefore, we would have to arrange it through a partial purchase of part of the property area as co-ownership. Are there any risks involved, and where can I find information about this?

Thank you very much!

Welche rechtlichen Vorschriften gibt es

No concrete ones. In planning law, the term appears in §22 (2) of the Land Use Ordinance without clearly defined criteria. The distinction is always a case-by-case decision, initially made by the building authority. Legal remedies can then be filed against this, and a court decides whether the authority's assessment was correct.

ist es u.a. möglich separate Eingänge und Heizungsanlagen zu haben

Basically yes. However, you have to convince your caseworker or their superior – or the judge, if you want to go that far.

Das Grundstück kann nicht geteilt werden wegen der Vorgabe “Nur Einzelhaus zulässig“.

I cannot understand the reasoning.

Gibt es da Risiken und wo kann ich Informationen dazu finden?

You are building a condominium and always have to deal with the co-owners. Whether that is a risk, I do not know. Legal basis: Wohnungseigentumsgesetz (WoEiG oder WEG)

Basically yes. But you have to convince your caseworker or their supervisor – or the judge, if you want to go that far.

Thanks for the answer. What arguments could one bring forward here? Unfortunately, I have the feeling that the gentleman from the building authority here in the municipality somehow has something against our construction project. Initially, he told us that we were not allowed to build on the property at all. Only the architect made him aware of a section in the newer land use ordinance that this is indeed possible.

What is strange is the following regarding the development plan: In our documents (building permit for the existing house), a closed triangle with a circle is listed as the symbol for the building method: according to the legend, detached building method and single and semi-detached houses are permitted. So we initially assumed this.
However, in the development plan at the municipality, a downward open triangle with a circle is apparently listed instead: that is, detached building method, but only single houses are permitted. That seems very strange to me and I don’t yet know how we should deal with it. That is the limiting point for a possible subdivision of the property.

Our architect told us that subdivision of the property is not possible since only a single house is allowed on the entire property. With a separate property, however, the new building would be defined as a semi-detached house. From what I have learned so far, we would therefore have to buy part of the property (without subdividing the property) and thus be co-owners of the property. The share would then be notarized in such a way that our new building is located on this part of the property and clearly defined.

Thank you for the answer. What arguments could be made here? Unfortunately, I have the feeling that the gentleman from the building authority here in the municipality somehow has something against our construction project. Initially, he told us that we were not allowed to build on the property at all. Only the architect pointed out a section in the newer building use regulation that this is indeed possible.

Strange is the following with the development plan: In our documents (building permit for the existing house), the symbol for the building type is a closed triangle with a circle: according to the legend, detached building and single and semi-detached houses are permitted. So we initially assumed this.
In the development plan at the municipality, however, a downward open triangle with a circle seems to be shown instead: so detached building, but only single houses are permitted. This seems very strange to me and I still do not know how we should deal with it. This is the limiting point for a possible subdivision of the property.

Our architect told us that subdivision of the property is not possible, since only a single house is allowed on the entire property. With a separate property, however, the new building would be defined as a semi-detached house. What I have learned so far is that we would therefore have to buy a part of the property (without subdividing the property) and thus be co-owners of the property. The share would then be notarized so that our new building is located on this part of the property and clearly defined.

? Is it not possible for you to subdivide the property and then build a single house? Then there would be two properties with two single houses, which is allowed after all!

We would like to, but the architect says it’s not possible...everything seems somehow strange to me. The floor area ratio and the site coverage ratio would also be sufficient for the new building and the existing house after the division of the plot...

Post the plan including the development plan [emoji4]