Your home is a shelter from the storm, figuratively and literally. Each structural component is intended to keep you and your loved ones safe. The roof, walls, windows and insulation are designed to keep water outside and the home comfortable on the inside. A membrane made of plastic or a combination of heavy paper and foil typically envelops the inside of the house; this is known as a vapor barrier and it is installed before the drywall. Proper installation around doors or windows ensures that a minimum of moisture makes it inside your home.
Vacuum the floors, walls and crevasses of the room thoroughly. When you install the vapor barrier, any dust or grime the film touches will be trapped between the barrier and walls, so you want the room to be as clean as possible.
Cut a length of vapor barrier to cover the entire window by at least 6 inches on either side. The barrier should reach from the ceiling to the floor. It should be about 2 to 3 inches too long at the floor.
Load staples in the staple gun. Position your step ladder so that you can hang the right corner of the vapor barrier where the wall meets the ceiling, ensuring that you are several inches to the right of the window. The vapor barrier will cover the width of the window with several inches to spare.
Climb up the ladder and staple the top right corner as close as possible to the place where the ceiling meets the wall. Staple the barrier every 10 to 12 inches to secure it properly.
Climb down from the ladder and position it to the left of the window. Climb back up and pull the barrier taut so there are no wrinkles or gaps in the sheeting.
Staple the top left corner at the ceiling and then continue stapling to secure the top of the barrier.
Smooth the left side of the barrier with your hand and staple down the side about every 10 to 12 inches to secure it. Staple the right side in this manner. It will look as though you have sealed in the window, but you'll adjust the barrier around the window as your last steps.
Cut an X shape over the sealed window, beginning about 2 inches beyond the window perimeter on all sides.
Cut out the window, using the points of the X as your guide. There should be a 2-inch gap between the window frame and the vapor barrier.
Cut a length of sheathing tape to secure the vapor barrier to the wall above the window, overlapping the perimeter of the window. Seal the rest of the barrier around the window's perimeter.
Pull back the vapor barrier at the floor and draw a bead of caulk along the wall near the floor.
Fold the vapor barrier under so that it clears the floor and seal the bottom of the barrier to the caulk, securing it in place.