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Metal roof sweating issue

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Al Givens
11/5/2010
I've made a building plan change midstream of construction. I was building a DIY 24' x 40' pole barn and have the frame work pretty much done. Now, I want to make it into a work shop/garage. I plan on using metal for the roof and sides, the sweating issue has now come into play. The truss's are up, 16" centers, purlin's attached 2' centers. Should I put a Foil-Foam-Foil underlay or some sort of double bubble overlay over the truss's before putting the metal on? Or, can I put the metal on and have the underside sprayed with polyicynene foam? I plan on putting a Foil-Foam-Foil ceiling up with some sort of insulation over that, also insulating walls.
Nate Libbey
11/5/2010
Al, The foil-foam-foil or double bubble should work will for this purpose. You could also put the metal on first, and then spray the underside with foam, but this tends to be a much costlier method of insulating.
Eric Novotny
An informed customer is the Best Customer!
11/5/2010
Unless the bubble radiant barrier is sealed up tight, you are going to have some condensation and sweating issues if you condition that space. It is not cheap but it is much easier to spray foam that area and get your vapor barrier tight that it is with plastic or other layers. You are still going to have to insulate that roof deck regardless if you want to use that space as conditioned space to some capacity. If you don't care much about losing heat through it, put a radiant barrier or poly layer and make sure the seams are tight.
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