Build 1 DH or 2 single-family houses on the plot?

...

You could both do without the distance between each other and thus build your single-family houses as close together as semi-detached houses are .... ?

I am quite sure that, among other things, the regulated clearance area cannot be waived for fire protection reasons. Explaining or justifying this here would go beyond the scope. Every building authority could comment on this.

Personally, I see no advantage at all in squeezing two single-family houses in there. The building envelope offers no freedom to expand or to design the house more freely. On 6 x 10 there is hardly ... oh, the space is not worth mentioning ;)

In addition, single-family house plots must have a minimum size. It depends on the municipality and the development plan (and infrastructure). Often in pure residential areas 500 or 650 sqm. In very rural areas even larger with a smaller floor area ratio...

You can still check whether there might be room for 2 single-family houses.

The check is quite simple:
a) 18 m width divided by two, without space in between, gives 2x 9 m width.
b) 18 m width minus 6 m gap in between gives 2x 6 m width, for each house a fourth outer wall and a fourth light side.
c) 18 m width minus 3 m gap in between gives 2x 7.50 m width, and for each house a fourth outer wall for heat dissipation, which, however, is useless as a light side.
Conclusion: semi-detached house.

whether the building distance could also be shortened.

Only between your two houses (for the semi-detached house down to zero). I see no option towards the neighbors. So always 18 m from the left corner of the left house to the right corner of the right house.

2 single-family houses are, in our opinion, more attractive than 1 semi-detached house.

With this opinion you are wrong for this plot (or only one fits). However, I find 9 m house width per side practical.

Clear statement. This is a DH lot. Or just a single-family house. Everything else is nonsense.

... says the Ostholsteiner who uses walking sticks for a walk around the property two detached houses! ... says the North German terraced house in Westphalia who knows many building plots under 200m². The plot is estimated to be 800m², leaving 400m² for each party if divided. The minimum distance area in BW is 2.50m. If the street-side development boundary is not a building line, you do not have to build parallel to the street. For the northern plot (north at the top of the plan?), a rectangular building is obviously not an option due to the building boundaries. But an architect can certainly design two decent detached houses here if there are no further unknown development plan restrictions (see ). Then, no violation of the minimum distance would be necessary. Such a violation would be possible under certain conditions (e.g. building end walls without openings, see §6 LBO_BW), but not advisable (see ).

O God...south German laying hen husbandry....,Karsten

Oh God... southern German laying hen keeping...., Karsten

3 comments, 3 times not helpful... thumbs up, Karsten.... The property is located directly on Lake Constance. The land prices here are simply astronomical. Here you get 110 sqm of living space in a single-family house built in 1970 sold for a modest €750,000. The Swiss buyers outbid each other by thousands of euros... so much for the topic "laying hen keeping"... there simply are no plots for ordinary mortals. Whether you want to interpret this as "laying hen keeping" is up to you. You seem to be in the fortunate position to have a bit more choice. Unfortunately, that is not the case for us, so we do not want to leave anything untried and want to find the optimal solution for both parties with the means (plots) available to us. It was merely about whether maybe 2 single-family houses would fit on the plot while observing the building regulations. Personal opinions are certainly welcome, but preferably in constructive form. Unfortunately, we are (still) not very experienced in the industry, so we rely on advice and opinions from friends, family, and forums.

Oh God... southern German laying hen farming...., Karsten

I grew up exactly where you live. My parents built several times in new housing developments and the plots there usually had less than 400 sqm.

Also, your other descriptions of the local conditions remind me more of stories from my grandparents than of the reality I experienced - lovable folklore, really.