The use of separate vapor retarders with unfaced insulation is becoming more common. They should face the warm-in-winter side of the framing. Four-mil, or thicker, polyethylene sheeting, available in rolls, is rolled out horizontally and stapled to the face of the framing, at top, bottom and the side. If one sheet of poly is not wide enough to cover the area and a second sheet of polyethylene is required, they should be overlapped on the stud space where they meet and stapled to adjoining studs.

Foil-backed gypsum board is also an effective vapor retarder. Other options for providing a vapor retarder include gypsum board manufactured with a vapor retarder or vapor retarder type paint, which may be used in renovations.