To add more insulation, remove the vapor retarder paper facing (asphalt coated?) just slitting it won't effect much; "Furthermore, the amount of vapor which diffuses through a building
component is a direct function of area. That is, if 90 percent of the
building enclosure surface area is covered with a vapor retarder, then
that vapor retarder is 90 percent effective. In other words, continuity of
the vapor retarder is not as significant as the continuity of the air barrier.
For instance, polyethylene film which may have tears and numerous
punctures present will act as an effective vapor barrier, whereas at
the same time it is a poor air barrier. Similarly, the kraft-facing on fiberglass
batts installed in exterior walls acts as an effective vapor retarder,
in spite of the numerous gaps and joints in the kraft-facing." From pp.5; http://www.buildingscience.com/docu...por-retarders/?topic=/doctypes/researchreport
Gary
component is a direct function of area. That is, if 90 percent of the
building enclosure surface area is covered with a vapor retarder, then
that vapor retarder is 90 percent effective. In other words, continuity of
the vapor retarder is not as significant as the continuity of the air barrier.
For instance, polyethylene film which may have tears and numerous
punctures present will act as an effective vapor barrier, whereas at
the same time it is a poor air barrier. Similarly, the kraft-facing on fiberglass
batts installed in exterior walls acts as an effective vapor retarder,
in spite of the numerous gaps and joints in the kraft-facing." From pp.5; http://www.buildingscience.com/docu...por-retarders/?topic=/doctypes/researchreport
Gary
