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Community and Q&A

Detailing Wall to Stem Wall Foundation

anukeen_sprout | Posted in Green Building Techniques on

Hi all, Attached is my proposed detail for my wall and foundation. I am in Zone 3 (northern California), but shooting for a more energy efficient space. I would very much appreciate this community to review my detail, and comment away. Anything I’m missing? Anything you would do differently? Here are the questions I have: 1) My WRB is the Huber Zip Sheathing, but there is 1″ of polyiso foam. Does it make sense to also use the polyiso as an additional WRB for the approved tapes? 2) IF water was to get to the Zip WRB, I’m thinking I want to keep the bottom open. Even if tape the foam, shouldn’t I leave a gap at the concrete stem wall? 3) This is termite country. The foam will be exposed at the bottom albeit 14″ above grade. Should I be worried about termites and other insects? If so, how do I protect the foam AND allow the Zip WRB to drain? (Could this be solved by using a different type of rigid foam?) 4) My board and batten nails are ALL going though the foam and through the Zip sheathing. Huber says this is no problem. Should I be worried about all these penetrations in my water and air barrier? Thank you GBA community! I love this resource!

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  1. Expert Member
    Akos | | #1

    1) Doesn't hurt but also not worth any extra work/cost. Houses need one proper WRB, ZIP is more than enough.

    2) Reality is that even if not taped, the foam layer will channel most of the water down and it will never make it to the ZIP. Any moisture that is there can dry through the gaps in the foam, another reason no to tape the foam seams.

    You never leave any foam exposed. Critters will find it. Always cover with flashing. Perforated J mold is the best something like this with the perf adjusted to rain screen gap+foam thickness:

    3) I'm not in termite country, so I can't help much. Definitely figure out your termite details including the foam under the slab.

    In your climate, full rigid under the slab doesn't save all that much energy and increases cooling costs. Perimeter insulation might be a better option.

    4) Nail holes never matter on siding. They don't leak water or air, I would loose no sleep over them. This includes the heads of the nails holding on the ZIP to the studs, they don't need to be sealed unless grossly overdriven.

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