insulation per fabril technical bulletin 721

jim hoffer
when reading fabril technical bulletin 721, it states that you can put a metal roofing over an existing asphalt shingles. add 2" X 4" pirlins and an underlayment (either over or under the pirlins) then is states that insulation can be added in between the 2 X 4s followed by a vapor barrier (such as 6 Mil plastic). My question is what effects does the insulation have and how does it interact with ventilation. My home is a two story with all of the insulation is above the ceiling and none near the roof. there are six soffits vents and two vent gable vents. If you add the insulation, you then have insulation at the ceiling below the ventilation, and insulation above the ventilation. 1. Will this insulation provide energy savings, or will the ventilation eliminate the savings? 2. is additional ventilation needed? 3. Is both a vapor barrier and underlayment required? This seems like an overkill to me, or do they serve different purposes?
Todd Miller
Isaiah Industries, Inc.
Jim, because this is specifically about one of our member manufacturer's products, please contact them direct. I would suggest emailing [email protected]
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