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Crawl space sealing – vapor barrier under or over wall insulation?

aklab | Posted in Energy Efficiency and Durability on

Hi, I’m working on creating a sealed, unvented crawl space and the information on this site has been very helpful. I’m in Zone 3, 100 year old house, brick foundation walls that are pretty tall for a crawl space, almost 4′. 

One question I can’t seem to find an answer to: should I put my foam board insulation against the brick, then vapor barrier over that, or vapor barrier first, with the insulation over it? Most pictures I see use the former approach, but maybe that’s because it’s more photogenic. 

I also thought about lapping the vapor barrier about 6″ up the walls, then foam board, then vapor barrier all the way over it. The XPS foam board is rated for ground contact but that might make it a little harder for subterranean termites and such to find it. Any thoughts?

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