What’s the point of the extension if the basement is supposed to be living space?
Building in the 2nd row, the front house and the 2nd house must have a common building structure. So it’s house-extension-extension-house. At least this way you have more space between the houses.
I would really like to build a detached house here, but if the building authority doesn’t allow it...
And of course it would be better to build without a basement if the house could be 20sqm larger. But it can’t! So heating, technology, laundry room go into the basement, and you can fill it up immediately, and also accommodate a guest room, etc. there.