Confusion about vapor barrier

Jay Wilks
6/28/2014
I'm ready to order the materials for my DYI metal roof, but I have one question.... I'm installing over the single layer asphalt shingles on my ranch home. I'm planning to run purlins along the rake, the ridge and across the roof paralell to the gutter line every 2 feet as the manufacturer suggests. Then I was planning to put a rigid foam insulation with an aluminum facing between each row of purlins. Do I still need a vapor barrier???? If so, should the vapor barrier be rolled completely over the top of the rigid foam and the purlins??? Or, should the vapor barrier be installed on the roof first and the purlins and rigid foam installed over that???? Thanks
Todd Miller
Classic Products, Inc.
6/28/2014
Unless there is something out of the ordinary about the rest of your home's construction, you probably do not need a vapor barrier. However, I would recommend a layer of synthetic roofing underlayment, either on top of the old shingles, or on top of your insulation and battens (preferably the latter).
Info @windowsonwashington.net
An informed customer is our best customer.
6/28/2014
No need for a vapor barrier as the shingles and underlayment and/or foam will all accomplish that. How is the roof vented currently?
Guest User
7/1/2014
Currently the house is vented with gable end vents. I will be installing a ridge vent and soffit vents along with the new roof. Also, do I need those rubber/foam closures on the bottom panels along the gutter line? Some people say you need them to keep insects out...others say not to put the closures in so the metal can breathe.... I'm confused.
Info @windowsonwashington.net
An informed customer is our best customer.
7/1/2014
No need for a vapor control layer. Attic is vented application. The foam enclosures are somewhat air open and will allow the roof to dry should water get behind them. Don't leave them open. Too many critters will get up there.

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