Inland development (second row)

Here again is an excerpt from Par. 19 Baunutzungsverordnung

(1) The floor area ratio indicates how many square meters of floor area are permissible per square meter of plot area within the meaning of paragraph 3.
(2) Permissible floor area is the portion of the building plot calculated according to paragraph 1 that may be covered by buildings.
(3) For determining the permissible floor area, the area of the building plot that lies in the building land and behind the street boundary line established in the development plan is decisive. If no street boundary line has been established, the area of the building plot that lies behind the actual street boundary or that is designated as decisive for determining the permissible floor area in the development plan shall apply.

You see, there is a before and after the street boundary line.

Many thanks YPG! Thus, the whole matter presents itself much more positively than previously assumed for both us (who can build the full 109 sqm with the house, disregarding the terrace) and our neighbor/seller (who could also build 109 sqm).

Thus, the whole situation appears significantly more positive than previously assumed, both for us (who can build the full 109 sqm with the house, without considering the terrace) and for our neighbor/seller (who is also allowed to build 109 sqm).

What is stopping you from asking the expert? – I have given you several hints about his "location"...

What is stopping you from asking the expert? - I have given you multiple hints about his "location" ...

I have actually considered asking a specialist lawyer. Does that make sense with such a question?

Who is this mysterious contact you mentioned here? Unfortunately, I couldn't make anything of the partly very cryptic hints...

I was actually considering asking a specialist lawyer. Does that make sense with such a question?

Yes, but it’s not necessary if you ask the expert in the forums.

Who is this mysterious contact you mentioned here? Unfortunately, I couldn't make sense of the partly very cryptic hints...

Just google, for example, "11ant Forum." Then you will find two of them (which are green or blue there, whereas this one is orange) and in both a user named Dimeto. He is a surveying engineer – not mysterious, but competent. Unfortunately, it can’t be made any less cryptic here.

our neighbor/seller (who is also allowed to build 109sqm)

Now you are overlooking your driveway. Although it counts toward the floor area ratio-2, 20m at 3m width is 60sqm and consumes the entire floor area ratio-2. In addition, the front property will still need a parking space and access to it, which will branch off from the house accordingly. And the fact that a terrace, under still to be clarified circumstances (with such issues, you also have to expect that the building authority lacks the corresponding knowledge), is not counted toward the floor area ratio-1 does not mean it is not counted at all. That would then be floor area ratio-2 again. I maintain that dividing at 0.2 is a shot in the foot. Viewed in isolation, right at the limit of buildability, the one with the driveway is literally blocking all possibilities.