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I am planning to install a corrugated metal (R-panel) roof on my upcoming build located in north central Texas. I am doing the work myself and have heard quite a few methods/opinions for the best way to install.
The roof will be an 8/12 gable with a large shed dormer on one side which will be a 4/12 pitch. Below will be an upstairs living space, cathederal ceiling with R-19 batting.
The methods I am considering now are decking/underlayment/metal or decking/underlayment/3/4 purlins on 24" centers with 3/4 rigid foam between them (or not)/metal. The rigid foam is an idea to reduce heat gain, not sure how effective it would actually be. I'm also looking into radiant barrier bubble foil below in the rafter cavities as an alternate idea for that.
Also interested in recommendations on OSB vs. plywood and what thickness of decking would be adequate for reasonable wind resistance, and synthetic underlayment (I'm considering Triflex XT or Dupont Protec 160) vs. 30# felt.
I prefer plywood. You could also incorporate a foil backed rigid foam for the best of both worlds and some above deck venting to get that heat moved out.
Would it be better to install the foil backed foam between horizontal purlins/strapping or directly over the decking with no purlins/strapping, fastening the metal directly to the decking through the foam?
Also, are there any synthetic underlayments that are best to use with metal roofs? I have seen that some synthetic products say they are to be used under shingle roofs only.
Ideally, a radiant barrier needs an air space to work best.
In that case, foam over the roof deck with purlins for a vent space will work best.
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