How to Install Poly Over Insulation

Unroll a sheet of polyethylene plastic. Lift the sheet up to the wall and extend it 4 inches past the wall's top header -- the horizontal board resting on top of the wall studs. Work from the center of the poly sheet towards the edges and secure the poly to the top of each wall stud with 1 staple, using a construction stapler.

Tug the poly straight down toward the floor to remove all the folds and wrinkles. Work your way up from the bottom and secure the poly to each wall stud it covers. Place 1 staple every 12 to 16 inches along each stud. Lift up a second sheet of poly, overlap the first sheet with the second sheet by 3 to 4 inches and secure it to the wall studs in the same way. Continue until you have installed a vapor barrier on all four walls.

Remove the poly covering all the electrical boxes using a utility knife. Cut as closely as possible to the boxes' edges. Reach inside the hole and pull the electrical box's vapor box through the hole and fold it down against the poly's surface. Apply a strip of seaming tape over the seam where the vapor box meets the poly's surface. Overlap the tape strips to make the seam airtight.

Place a tube of acoustical sealant in a caulk gun. Cut off the tube's tip with a utility knife. Squeeze a bead of sealant along the bottom surface of the foundation board or header. Lift the 4-inch poly flap up and press it into the caulk bead. Secure the poly with a staple every 12 to 16 inches.

Apply a strip of seaming tape along the seam of each overlapping poly sheet, from the top to the bottom.