How to Install a Vapor Barrier on the Ceiling

Check that your light fixtures have a vapor barrier box mounted behind them. If not, take the time to remove each light fixture and install boxes around them. If you do not, warm air will find its way out of these gaps.

Unroll the polyethylene sheeting across the floor, parallel to the ceiling joists. Use a scissors to cut the sheeting to the room's length.

Lift the sheeting's corner up to the room's corner and use construction staples to secure it to the wall's top plate -- the horizontal board running over the wall studs. Move down the length of the polyethylene sheeting and place a staple in the top plate, behind each wall stud. Remove all the wrinkles and folds as you go along.

Move 6 to 8 inches down and lift the polyethylene sheeting up to the ceiling joists. Remove all the wrinkles and staple the sheeting in place. Continue all the way down the sheeting's width, stapling it to each ceiling joist.

Move another 6 to 8 inches down the polyethylene sheeting's length. Lift the sheeting up to the ceiling joists, smooth it and staple it in place. Continue in this manner until you install the plastic sheeting from wall to wall.

Lift a second polyethylene sheeting up to the ceiling. Overlap this sheeting with the first sheeting by about 2 to 3 inches. Staple this sheeting to the ceiling joists. Continue until you install the vapor barrier over the entire ceiling.

Cut holes around the light fixtures with a utility knife. Reach inside and pull out the vapor barrier box and smooth it over the polyethylene sheeting. Run strips of seaming tape along all four sides to make it air tight. Run strips of seaming tape along the seam of the overlapping polyethylene sheeting.