Meanwhile I found some related threads.


BUG: Sloping slope works as soon as new level is created
Windows in a inclined roof


If the answers to those threads are still valid, my question is answered.

It is a pity that windows have to be positioned before ex-/importing them. I am planning ...

I followed the Tutorial for sloping roofs and ceilings, dormers and more with success to create a sloping ceiling. Then I was surprised to find out that it did not work with my own model.

After long hours of testing and checking my coordinates I found out, that the slopes are applied if I remove ...