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Community and Q&A

Put exterior wall on top of ICF foam?

paulson123 | Posted in General Questions on

I am building a wood building slab on grade in North Dakota. I poured ICF frost walls, keeping the wall down 3 inches from the top so that i can cut inside form down and pour the slab tot he outside form to prevent heat loss from radiant floor. If I put the wall flush to the outside of the slab, how do I deal with the 2 inch foam on the outside? Z flashing over it? A friend said he just put his 2X6 wall flush with the outside foam, so he has 3 1/2 inches on the slab and 2 inches on the foam. Is that a good idea? Not sure how to deal with this. I could use a 2X8 wall and have more wood on the slab, but that would be expensive!

Any suggestions would be greatly appreciated. Thank you!

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  1. GBA Editor
    Martin Holladay | | #1

    The first step for you is to contact the manufacturer of the ICFs you are using and ask for access to construction details for their products. Many such details are available online; check the website of the ICF manufacturer.

    One way to handle your detail is to install 2 inches of rigid foam on the exterior of your wall sheathing; it's also possible to use Z-flashing. You may want to consult an engineer to discuss the maximum amount of cantilever (over your foundation foam) permitted for the bottom plates of your walls.

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