Chris writes from Jacksonville, Florida: "I'm preparing to add insulation (blown in) between the ceiling joists in the attic of a small commercial building I own that was built in the '50s.

"The building originally had 1x3 furring strips nailed perpendicular to the bottoms of the ceiling joists with acoustical tiles stapled to bottom (interior side) of those furring strips. During a later remodel, the previous owner installed a suspended grid ceiling about a foot below the acoustical tiles with batts of unfaced insulation laid on top of the ceiling tiles. (I think that as of 2006, FL code no longer allows that practice.) I realize that insulation is not doing much the way it's installed.

"With the penetrations of the original acoustical tile ceiling (lots of places where electric conduit and AC vents were added to the grid ceiling down through the acoustical tile ceiling) I know I have large amounts of conditioned air moving up into the uninsulated attic and out through the ridge vent.

"I am thinking of using visqueen as an air block stapled to the tops of the ceiling joists before blowing in the insulation. Or do I need housewrap or something else for this? Am I thinking right here?"

Answer: You may want to inspect the existing insulation to make sure you do not have a vapor barrier already in place. If you are uncertain, I recommend using a housewrap that is breathable, such as the very nice PINKWRAP® housewrap from Owens Corning.