Insulation, Radiant and Vapor Barriers - vapor barrier?
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parkway
10-31-06, 05:35 PM
I am planning on blowing cellulose into my attic. there is currently no vapor barrier. Any suggestions on what and how to apply it? I assume it would not be a good idea to skip it? (the ceilings below are lathe and palster, it that makes any difference....)
twelvepole
10-31-06, 06:30 PM
If you have never been to a home show and have not seen the blown-in insulation guys demonstrate the low air permeability of cellulose versus fiberglass insulation, you have missed out. These guys get really excited.
By virtue of the low air permeability of blown-in cellulose, many say that if sufficient attic ventilation exists a vapor retarder is not needed. The key is if its sufficient--a net free ventilating area equal to 1/150 of the attic floor area.
Others will tell you that a vapor retarder is worthwhile in cold climates to prevent condensation problems and to not take a chance. Some recommend a combination of faced fiberglass batts with vapor retarder turned down toward heated area below along with blown-in insulation. Others recommend a vapor retarder ceiling paint below. Still others recommend a polypropylene vapor retarder.
One way to clear up the confusion is to check with your local building code office to see what their requirements are. In the meantime, seal all gaps, cracks, crevices where warm, moist air can enter attic from below.
By virtue of the low air permeability of blown-in cellulose, many say that if sufficient attic ventilation exists a vapor retarder is not needed. The key is if its sufficient--a net free ventilating area equal to 1/150 of the attic floor area.
Others will tell you that a vapor retarder is worthwhile in cold climates to prevent condensation problems and to not take a chance. Some recommend a combination of faced fiberglass batts with vapor retarder turned down toward heated area below along with blown-in insulation. Others recommend a vapor retarder ceiling paint below. Still others recommend a polypropylene vapor retarder.
One way to clear up the confusion is to check with your local building code office to see what their requirements are. In the meantime, seal all gaps, cracks, crevices where warm, moist air can enter attic from below.