Is a vapor retarder required?
Jim writes from Detroit, Michigan: “I have an attached garage and heat in it, the ceiling was drywalled only with no vapour barrier between it and the attic, I want to insulate the ceiling, is a vapour barrier required? The attic is ventilated, and also is the insulation supposed to be put right up to the edge of the attic sealing the air space between it and the soffit and eaves troughs?” Answer: Always check with local building codes to find out their requirements. Varpor retarders are not always used in this type of application. We do recommend a minimum one inch air space between the bottom of the roof deck and the top of our insulation. Owens Corning recommends that you have a balance ventilation system in your attic, meaning that an equal amount ventilation should be located in the eaves or overhang and at the ridge or within three feet of the peak of the roof. Vent openings should conform to or exceed current construction standards, which usually call for a minimum of one square
