Guest User
8/13/2010
Could tell me the minimize roof pitch required for a metal roof? Also, we're thinking of a SIPS panel under the metal. What can you tell me about the benefits/problems of a metal and SIPS panel combination. Thanks
Guest User
8/15/2010
The minimum roof pitch varies from manufacturer to manufacturer and panel style. You need to look at all the different manufacturers' styles and their technical data. When you use SIPS, make sure you allow for ventilation between it and the backside of the metal panel. If you don't allow for air circulation, the panel will rust out from the backside, as condensation will occur. To make your installation easier, I suggest you use a nail base polyiso of the R factor you desire.
Guest User
8/15/2010
Why would the panel sweat where it meets the SIP? If they are using a 6" panel thickness that is more functional insulation value that most homes that an unconditioned attic space. I would not recommend applying any panel directly to a plywood substrate without some sort of underlayment (preferably a synthetic woven polypropylene). Metal is going to sweat because of temperature differentials and moisture content. If there is no moisture leaving the structure (SIPs can me made to be air and moisture tight) the only source of moisture is atmospheric at that point. If you have sufficient insulation on the roof deck (SIP or applied) ventilation is redundant and unnecessary. Over deck roof venting is great if you don't have enough insulation and you are worried about heat loss from the structure and the resultant melting and Ice damning.
Todd Miller
Isaiah Industries, Inc.
8/28/2010
You want to make sure that the SIPS panels are joined properly and have a vapor barrier on their bottom side. Most metal roofs can be used down to 3:12 and a few to 2:12 pitch. Roofs less than 2:12 require a mechanically seamed standing seam panel.
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