New Construction Method Metal/Foam

Guest User
I building a 32x24 cabin with a vaulted ceiling and a loft bedroom. I used engineered trusses and installed 2x4 furring strips horizontally across the trusses. My plan is to install synthetic vapor barrier on top of the furring strips then the metal. Also, I am going to have the roof insulated with foam insulation. My question is, is it permissible to spray the insulation on the underside of the synthetic moisture barrier? Will it adhere? Will it drupe down after spraying? Is there a need for ridge ventilation with this combination? Thanks in advance, Duane
Todd Miller
Isaiah Industries, Inc.
I am a little concerned about spraying onto your vapor barrier, It could indeed make it sag and potentially even have the foam crack or separate from it. Ventilation is kind of a different question and depends a lot upon how sealed the attic will be. If you all seal the entire attic with foam and not have any intake vents, then you do not need ridge vents. Here is an article on ventilation that may be helpful:
Eric Novotny
An informed customer is the Best Customer!
Duane, Todd is spot on in that I spraying to the backside of the underlayment/vapor barrier is not preferred. If you could stitch in some rigid foam the full length to the back side of the furring strips, you would then spray to the backside of the foam and have a sealed attic design.

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