Spray foam on crawl space rim joists – vapor barrier still needed?
Doing a crawl space encapsulation job. Customer wants spray foam on the rim joists plus I am doing a full floor system with poly vapor barrier.
Question: If I am spraying 2 inch closed cell on the rim joists, do I still need to extend the poly barrier up the foundation wall to the joists, or does the foam take the place of the vapor control at that location?
Climate zone 5 here (Indiana). IRC 2021 applies.
My understanding: closed cell foam at 2 inch IS a Class II vapor retarder, so the poly is not technically needed at the rim joist location. But I want to make sure there is no air leakage path between the poly on the floor and where the foam starts on the rim.
Also: should I foam the sill plate area before the rim joist, or foam both together?
Indiana CZ5 contractor here. Yes, 2 inch closed cell on rim joists is a Class II vapor retarder – you do not need poly there. My process: spray the sill plate and 6 inches of foundation wall first, then move up to the full rim joist. This creates a continuous air seal. Then lap the ground poly barrier up the foundation wall 6-8 inches and tape it. Perfect thermal and vapor bridge with no gaps. I have done it this way for 5 years with zero issues.