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Old 09-02-2012, 02:41 PM   #1
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New metal roof -how to prevent condensation problems

I am building a shop using 40*64*16 pole barn type construction in western NY, but many features will be more similar to standard home construction: will have continuous in concrete pex heating, will have interior vapor barrier all walls and ceilings-- so attic will be cold.
roof will be 9/12 pitch, Fabrel metal over purlins, continuous ridge vent, and soffet vents. Shop ceiling will be horizontal ceiling joists with bat r30 insulation and vabor barrier below that.
I'm mainly concerned about how to prevent condensation on the uderside of the metal roof-- and having that drip down onto and destroy (over time) the glass bat insulation insulating the shop ceiling.

I've read posts on this forum suggesting foam against the metal roof, but I'm wondering if there is a less expensive way to prevent the condensation.
Also, can I use a reflective foil somehow under the metal (perhaps between the roof joists and purlins so there would be a continuous space for air flow from ridge vents to the soffet vents) to cut down on heat gain in the "attic" in our hot summers/cold winters.
Thanks in advance,


Last edited by rvander1; 09-02-2012 at 02:49 PM. Reason: Sorry about the duplicate post--
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Old 09-03-2012, 11:37 AM   #2
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Skip the foil layer. No application value in upstate NY.

Makes sure the ridge and soffit vents are correct and balanced, air seal the attic floor, blow in an R-50 cellulose.


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Old 09-04-2012, 01:31 AM   #3
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Use an absorbent/breathable type underlay, this absorbs any moisture that drips, and holds it until it evaporates. Standard practice here.
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Old 09-06-2012, 05:12 AM   #4
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To add to my previous post: Here's an example of a metal roof with the foil type underlay and no ceiling, typical of warehouses/factories here... without the foil, condensation would be a serious problem, given the building's current use as a kendo dojo.
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