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Designing a home on the West coast of Florida shore with two low-sloped, standing seam metal roofs (1:12 and 1/4:12). The low-slopes have been approved by the metal roof manufacturer. We typically like to vent below the metal, above the sheathing. With such a low slope, is there still a benefit in venting below the metal roof? Are there any recommendations on how to ventilate in this manner? "Viper CDR Vent," "Sharkskin Roof Underlayment," and batten systems were all options we were considering. Thanks, William.
It's not unusual on projects similar this for me to hear of closed cell foam being used, often eliminating the need for ventilation That said, I'd like to see ventilation beneath the sheathing based on your description. Underlayment is required by code between the decking and the metal roof. Have you asked the metal roof manufacturer to review plans and help you work out these details?
Hello Todd, thanks for the comment. The manufacturer simply stated that they do not have a standard ventilation detail. We are simply wondering if a small air space directly below the standing seam metal is worth it with such a low slope? The ventilation should theoretically be useful to keep the roof cool and to wick away moisture, but if the roof is flat and does not create a stack effect, will the air space actually do anything? Thank you
Thanks. So, one of the concerns is that, with direct contact between the metal and the roof deck, the metal will drop the roof deck temp enough to cause condensation on the underside of the roof deck. Having ventilation to whatever degree you can below the roof deck will help carry out moisture and warm air originating in the living space. Having an airgap on top of the roof deck will provide a thermal break to help reduce the transfer of cold (or heat) from the roof surface to the roof deck. Here's a link to an industry webinar that may be of help to you: https://www.youtube.com/watch?v=NYwD9CWveKY
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