Emmanuel:

On a brainwave I tried a new way to have two windows on top of each other.

First I imported a box and made it insertable. Then I combined the box with a window below, and a window on top of it. I then combined these three objects in a group, hoping the group would inherit the insertability of all three components. Guess what? It does!

This is a great way to have more flexibility when designing walls with windows over doors, etc etc.

There is just one snag: the windows lose their transparency. Do you think there is a solution for that?

Hans