Extension to an existing "multi-family house" - boundary distance?

Hello,

I have the opportunity to extend the existing house of my grandfather. His house is approximately 13.5m long * 9.75m wide * 11m high. The extension side is constructed as a firewall, as it was originally planned to basically build the house again there. However, this was not realized. What should definitely be possible is to catch up on this construction now, but it is too large for me. Additionally, I would like to have a garage. Therefore, my plan is to build a garage as a boundary development, and then build my residential house attached to it, which would then be roughly square. Moving it further will be difficult, as the property ends at some point. In my opinion, the advantage would be that windows could be installed again on the upper floor, from which one wouldn’t have a particularly nice view, but there would be some light. The development plan allows for 3 full stories; I would like to build a 1 1/2 to 2-story house, with a height of about 7-8m. Are there any opinions on this, especially regarding building law issues? The applicable law is Lower Saxony. I can also upload pictures/plans, I am just on the go right now.

Thank you very much in advance for the input.

The multi-family house has either fully met its boundary distance on its own property, or an offset acceptance must be recorded in your land register sheet. Or - see the development plan - semi-detached houses are planned, then both properties may have an obligation to build an extension (which, in my opinion, would not be fulfilled with a garage). "Undoubtedly" does not exist in planning law - after grandpa's building completion, the development plan may have changed.

I am attaching the relevant information from the still legally binding development plan and a sketch of the property. It is clear that a building encumbrance would have to be registered, but is it even possible with the windows on the upper floor?

It is clear that an easement would have to be registered, but is it even possible with the windows on the upper floor?

Not today it would have to, but back then it had to – or better: would have had to, if we were talking about a neighboring property. According to the plan, however, it is probably from a part of a larger property that has not yet been built on, with the mentioned building. Of course, you could have that divided now, with a setback easement or only beyond the setback area of Grandpa’s house. And that has windows on this side, despite the annex planned back then?
In any case, the plot is located in a [SO]. Either your part would have to be incorporated into the neighboring WA section after the division, or I see you having to build shops on the ground floor.

No, the house has no windows on the side, see attachment. I could only imagine having windows on the side for my new build, but it is also possible without them.

The SO area is of course another "problem," Grandpa has not had his for about 10 years, the neighbor to the east also gave up his shop years ago and converted it into residential use. I do not know the legal actions taken by those neighbors today, but I could find out. Let’s put this side issue aside for now.

The SO area is of course another "problem", [...] Let's put this side issue aside for now.

That would be counting without the host, the side issue in war is called "front".