Thx a lot for your replies!
So its not a general problem rather then incompatible or bad modeling for sweet home 3D?
Since we are at it, i would have a followup question if its not to much

...concerning importing textures. Maybe you can also help me out here or i will simply open a new thread.
Anyway:
Can u skale textures after importing them?
Why i ask? -> while importing textures you have the option to skale textures, but i sometimes cant seem to find the right skale for my objects for them to connect right. So i "remport" and skale again and again until it suits my objects.
Or is there anything i have to check while importing and skaling?
Again, thanks a lot already!