House construction planned, what sums must one reckon with today?

If closed development is permitted, of course you can do that. But with us, open development is specified. Although we have also considered that my girlfriend would buy the plot to the south and build a garden h...Tiny House on it. Meanwhile, we have a neighbor again, so that is settled for the time being.

We are also building on both plots due to building obligation… for us, it will be two unequal semi-detached houses…

If closed development is permitted, of course you can do that. But for us, open development is required.

Semi-detached houses are not "closed development" - "o" needs a gap at least every 50 meters, which even rows of six terraced houses usually still fulfill, semi-detached houses all the more so.

Ok. So why does "open" development even exist then? ;) And are buildings allowed to extend beyond property boundaries just like that?

...
And buildings across property boundaries are just allowed like that?

If encumbrances have been registered, often yes ... (unless something else speaks against it, but that is clarified before registering a Baulast)

Why is there even "open" development then?

To be able to mandate it where closed development is to be prevented. Letting the fire department into block perimeter courtyards would only require driveways. But if a hundred-meter-long row of houses allowed no cross breeze, it would become a wind tunnel. As a rule, development is already loosened by many development plans prescribing the type of house, whereby house groups (H) are only scattered to a small extent between the E and E/D areas.

I am now at least on the waiting list... However, the plots have not yet been transferred to the possession of the provider. That is supposed to happen in the next few months. So no plots have been sold yet. As a local resident, I apparently have the right of first refusal. Let's see what comes of it.