Question How to move terrain straight up ?

I have a house that should be half in the ground because of a basement. But when I somehow do that with the usual tools, the heels always have sloping edges that penetrate through the basement walls. How can I move the terrain straight up without creating such strong inclines as in the pictures and thus the terrain not slipping through the cellar walls?

 

it isn't possible to have it exactly straight up, for the same reason you can't have a graph with a vertical line. You would have to have an infinite terrain resolution to have it go straight up. Best you can do is increase terrain resolution, or cover something on top of the terrain in that area to hide the problem

 

I have a Basement Stairway that goes up and the terrain should dock on the basement stairs, taht comes from under the terrain.
But I think the easiest solution is to make the basement walls bigger to cover the terrain penetration.