Should I vent polyiso roof insulation in a Hot/Dry climate?
Hello all. I am helping some friends retrofit their existing roof on a 1960's ranch stryle house. They would like to strip the current roof system and replace it with polyiso foam board (thickness to be determined), and standing seam metal roof system. My question is: should we create a vent between the attachment sheathing and the polyiso, or not. It can get to 110 F in the summer, and down to 15 F in the winter here. Any and all suggestions greatly appreciated
Asked by David Bushlow
Posted Tue, 03/02/2010 - 02:43
Edited Tue, 03/02/2010 - 06:25
Posted Tue, 03/02/2010 - 02:43
Edited Tue, 03/02/2010 - 06:25
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David,
Venting is not necessary. However, to avoid potential ice-dam problems (assuming you have snow during the winter), be sure that your insulation thickness is adequate. You want the R-value of your polyiso to (at a minimum) meet current code requirements.
Posted Tue, 03/02/2010 - 06:19
While roof orientation and color have more effect on sheathing and attic temperatures than roof venting, a vented roof always outperforms an unvented roof and is more durable (except, perhaps, in very humid climates) because it allows quick drying of roof sheathing if it should ever get wet.
If the polyiso is foil-faced, a vent cavity will also become a radiant barrier to summer solar gain.
Posted Tue, 03/02/2010 - 12:21