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Community and Q&A

EPS over concrete filled concrete blocks

Kevin Lesh | Posted in Energy Efficiency and Durability on

New construction, concrete block filled with concrete and rebar. Would like to have 4 inch EPS (2 two inch layers). Recommendations for securing foam to the concrete block, vapor barrier placement, and proper method to attach siding over the foam.

Thanks, Kevin

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  1. GBA Editor
    Martin Holladay | | #1

    I assume you are talking about an above-grade wall, and I assume you want to attach the foam to the exterior. Is that right?

    What type of siding are you using?

  2. Kevin Lesh | | #2

    Martin, Thanks for the reply. Yes, above grade and am open to siding type, thinking about vinyl. Plan on insulating below grade as well so open to suggestions there as well.

    Thanks, Kevin

  3. GBA Editor
    Martin Holladay | | #3

    You can attach rigid foam to your concrete block wall with Hilti IDP fasteners.

    Many types of siding can be attached to vertical furring strips; however, there is some controversy about whether or not vinyl siding can be installed over furring strips. (Plenty of builders have done this successfully, whether or not the vinyl siding manufacturers like it.) For more information on this topic, see Can Vinyl Siding be Applied Over Furring Strips? and Fastening Furring Strips to a Foam-Sheathed Wall.

    Vertical furring strips are usually attached through the foam with long screws. In your case, you would want to use Tapcon screws to attach the furring strips. Tapcon screws are available up to 6 inches long:

  4. Mike Collignon | | #4


    I've never met a person more knowledgeable about masonry construction than Dennis Graber of the National Concrete Masonry Association. You can contact him at [email protected].

  5. Kevin Lesh | | #5

    Thanks again for good info. Do you have recommendations for vapor barrier placement, on top of the eps or under it between the foam and concrete block? Rather than furring strips would I be better off with a layer of plywood under the siding rather than using furring strips?

    Thanks, Kevin

  6. GBA Editor
    Martin Holladay | | #6

    Four inches of EPS has a perm rating of less than 1 perm and is therefore already a vapor retarder.

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