CedAir roof ventilation mat under standing seam roof?
I am building the style of roof shown in the attached photo. Except, I’m using Corten standing seam roofing instead of shingles. I’m also using Sharkskin Ultra SA as both my air barrier and roof underlayment. I have 9″ of high density EPS for an R 45, and am using 1/2″ plywood, instead of OSB. Building in southern Idaho.
Against what I was always taught, and led to believe, I decided not to ventilate…just as shown in the photo. I based this largely on my take-away from Joe Lstiburek’s writing and lectures. In hindsight though, I’m sort of wishing I had ventilated. At this point (I have the roof completed sans the standing seam)….there’s no way I’d consider adding another roof over what I have to provide true ventilation.
By pure chance, I was offered some CedAir roof ventilation mat. It’s not something I’d normally consider. However, I got the impression it was either going to be given to me free of charge….or for a good deal. In looking at it though, I wonder if it could cause more problems than it might solve. In my case at the moment though….I can’t help but wonder if I shouldn’t give it some serious consideration….mostly for a way for some heat to escape.
Thoughts?
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Replies
deanbowman,
I'd definitely use it under wood shingles, I'm just not sure it adds much under metal.
What worries me are the gasketed fasteners. Installed over a mesh product I'd be afraid two things might happen: The gasketed fastener may depress the panel creating a dimple. Or without a solid substrate, the gasket may be too loose and let in water.
I am working with a company who sells metal shingles, and one of thier big selling points is energy efficiency . I was trying to find where I read it, but essentially a white standing seam panel added more heat to the structure then a dark metal shingle, due to the majority of the shingle not touching the substrate. I doubt that you will notice much with that much foam though. What kind of standing seam are you using?
Thanks, Malcom and Idahocottage.
To answer your question Idahocottage, I'm using a 1.75" tall snap lock standing seam (18" width) with clips, and a thermally applied butyl sealant.
I got to thinking about the corten steel, it will have a pretty low reflectivity rate, that will cause it to transfer more heat into the building. The cedar breather seams like a good idea if it is inexpensive.
We were working on a matte black standing seam roof last winter, and on the north side of the roof the snow was powder, and I threw a snowball onto the melted off south side, it was steam before it reached the eave. Metal gets hot, and it moves, your panels will move freely, but anything poking through might not. Also trim can be a challenge like that. I am still trying to figure out how to attach large metal fascia, and allow it to expand and contract,attaching roof trims to it pins it as well. If anyone has any good ideas let me know.
Idahocottage,
Western States Metal Roofing, Sheffield Metals, and Bridger Steel all have installation guides with excellent details. I'd recommend looking at them. They show how to do fascias without exposed fastners.
DB