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How thin can closed cell foam be applied Post New Topic | Post Reply

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Mark Peterson
Posted: May 30, 2014 12:19 PM
How thin can closed cell foam be applied
I am attempting to insulate the underside of the roof of a pole type machine shed. To keep the costs in line yet maintain some R value I am installing some 3" Styrofoam in between the 2x4 purlins. I was hoping to then spray closed cell foam to help lock in that Styrofoam, seal the joints between the Styrofoam and 2x4s, and create a vapor barrier on the warm side of the space. My questions relates to the expansion properties of this spray. Is it feasibly possible to spray this thin enough to keep the expansion down to the 1/2" space that is available after I place the 3" Styrofoam? I want to place steel panels over the cavity and don't want to have to trim excessive amounts of foam. The 3" Styrofoam came from a recycled source so wasn't privy to selecting 2" or something that gave me more space. If the foam cannot be applied that thin I may just have to apply around the cracks and figure out something else for creating the vapor barrier.
Posted: May 30, 2014 05:16 PM
Closed cell foam needs to be applied at a minimum of 1/2". If you only have 1/2" space, that is going to be impossible without trimming. In addition to that, most closed cell foams need to be 2" thick in order to be a class 2 vapor retarder. BaySeal closed cell foam is a class 2 vapor retarder at 1".
Good Luck,
George Spanos

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