Floor plan design of a brick house with approximately 145 sqm

We would then be chain houses - I’ll write an email to the building authority.

I wouldn’t do that!
An email gets rejected quickly. Much too impersonal. The first step would be to go to the neighbor anyway, unless you want to pay the 70K alone.
And then I would prepare that strategically a little bit.

We would certainly only put parking spaces or a garage there.

The heat is getting to your head!

"Not possible" is often relative.

Well, with f.i.v.e. green bills per square meter of building land (!), this "relative" in my opinion already fairly sharply borders on "absolute" for the average budgeter.

We would certainly only put parking spaces or a garage there.

That much money just for parking spaces - seriously? - the world is going downhill in style, what kind of R- or W-salaries are we talking about here?

So the community is considering it as an option. However, we would not really change anything about the house, since with a significantly larger house the price would also increase further. For now, we are just waiting it out – over 40k for parking spaces is really quite expensive. Maybe the price will eventually drop to a level that suits us.

Well, with f.i.v.e. green bills per square meter of building land (!) this "relative" in my opinion already borders quite sharply on "absolute" for the average budgeters. Such an amount of money just for parking spaces - seriously? - the world is going downhill in style, what kind of R- or W-salaries are we talking about here?

I don't see it that way, just for parking spaces... I rather think that one could then plan a real semi-detached house on 280m² of land. It doesn't even have to be bigger than your current house, , but everything around it would be significantly more relaxed. The plot would be much better usable than if simply a strip 3.5m wide were added on one side (which, from today's perspective, would have to have a wall to the middle house, no windows - which would also be completely unnecessary if there were none at all...).

Don't understand either. How do you come to the conclusion that the house needs to be made bigger? Only the plot gets bigger. Here you go - I hope it roughly comes across (grey = before, red = semi-detached house): Now enough parking spaces in front of the house. House size exactly the same.