2 level deck

[Katalyst777]

Make sure each of the decks is an enclosed room (use Invisible Walls or Invisible Railings if an actual deck railing isn't there), then open the Room Specification dialog for you first deck and set the appropriate floor height and click OK. Do the same for the second deck.

The steps in this article should help - http://www.homedesignersoftware.com/...?faqNumber=901

Pretty sure that there is a section in the Users Guide on this too, depending on your version.