Spray foam directly on underside of roof?
I have a conditioned attic, currently insulated with R19 fiberbatts between the rafters. No airsealing, hence I want to remove the fiberbatts and spray 3 inches of closed cell spray foam in before putting the fiberbatts back in place. The attic is unvented, for instance no ridge vent exists. Should I put any membrane or the like on the underside of the roof sheathing before spraying the foam in ? I was thinking that would help with keeping the insulation intact in case the roof needed repair later on?
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