Residential construction on existing building - parents' property

The last two answers are heading in the right direction: You must first clarify (or have clarified) whether an increase in the number of full or non-full floors is permitted under planning law. This also includes the utilization indicators of the property (site coverage ratio/floor space index), which are specified in the possibly existing development plan. From this, it must also be determined whether two or more residential units are allowed. If there is no development plan, the concept of adding floors must be officially confirmed in a preliminary building inquiry, including proof of setback areas and a sufficient number of parking and bicycle spaces.

The second important aspect concerns the structural prerequisites for adding floors: the existing construction must be capable of bearing the additional loads and transferring them down to the foundations. Requirements for soundproofing, fire protection, and the 1st + 2nd escape routes must also be checked. For two residential units, a separate staircase may need to be inserted into the existing building or added on the outside.

You should have the initial situation analyzed by an architect experienced with old buildings and have realistically possible scenarios for adding floors developed, if this is fundamentally feasible. For this purpose, you can gain access to the building file (archive of the responsible building authority) through your parents and have everything copied that is important for the architect and the preliminary design: building plans of the building permit, existing structural analysis (drawings + calculations) + the building description.

The question of financing and further ownership law aspects of the house extension arises once a basically approvable preliminary design has been developed.

PS. Some points have already been answered in the meantime.

Should not be a problem, next door 4 floors of terraced houses were spread over 10,000 sqm, and several floors have already been approved for the building. But I will check it.

With something like this, it also always depends on the number of parking spaces, connections, consumption, etc. So not just on the building. But it sounds promising at first.

Two more floors are allowed to be built on the building

Also structurally?

A 4-story townhouse is still one residential unit. Adding 2 more residential units to an existing building with probably one residential unit should be clarified. As already stated, this can trigger additional parking spaces for cars, it may generally not be desirable, etc.

Hello

here in Düsseldorf and Cologne they even pressure the house owner to add one or two more floors on top. This is happening to a friend of mine right now. 3 floors, 6 residential units. He was just asked to build one floor higher. He gave the authority the middle finger.

Steven

The building is currently a catering business. There is enough space all around for a possible staircase, parking spaces, etc. The roof's statics have been designed so that two additional floors can be added. On the neighboring property, a total of 27 residential units, including townhouses and granny flats, have been built. However, I am checking the points you mentioned to, of course, have the GO before further planning. That is exactly the INPUT I was hoping for. Thank you all for the critical input!

Hello my dears,
the whole thing was postponed a bit because of Corona. But it is not urgent.
2021 will be the year of planning. For that, I first want to educate myself a bit, organize consultations, and plan everything calmly.
Can you specifically recommend sources, books, etc. on the topics of "Aufstockung", "Hausbau Grundlagen", "Hausbau Finanzierung Grundlagen"?

Looking forward to your tips - have a good start into the new year, everyone! Stay healthy.