I'm getting ready to start hanging drywall on the ceilings (ceilings were previously acoustic tile stapled to ferring strips) in my project house and one of the issues that I've run into is that the with the strips removed I'm going to have about a half inch gap between the top of the drywall on the walls and on the ceiling and I was wondering if it would make sense to install some half inch foam board to close that gap rather than having to mud up the gap or cover with trim. Has anyone tried this?