Emmanuel,

I also imported the staircase, and, after checking Options -> Export two sided faces in Sketchup, the staircase exports correctly, and can be imported without problems.

The strange thing is that when I check staircase in step 2 of importation, the staircase does not make a hole in the ceiling. I checked height, and made a photo in Q3 with the VV.

When I use the furniture modification wizard, the square for staircase is unchecked, even though I checked the box when importing.

Hans