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Community and Q&A

How are utilities installed on a foundation wall with interior rigid foam?

Michael Schonlau | Posted in Green Building Techniques on

How are electrical and other utilities installed on a basement foundation wall (8″ poured concrete) that has 2″-3″ of rigid foam insulation installed on the interior side? We have some sections of the basement walls we plan to finish right away and others where we only want to insulate and add electrical for now. Are the utilities installed over the foam or does the foam typically get notched out? We are planning to build the stud walls against the foam and insulate the cavities with dense pack cellulose for both the walls we finish right away and the walls we finish later.

Thanks in advance for your feedback.

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  1. Riversong | | #1

    If you're going to be finishing all the basement walls at some point, then stud them out now so the wiring can be installed in the stud cavities and the boxes placed at the proper depth for future drywall.

    It makes no sense to tapcon conduit and metal boxes to the concrete if the wall will be interiorly insulated and later extended and finished.

    You could fasten strapping through the foam into the concrete and attach wiring to that, but that creates thermal bridging and requires later rewiring.

  2. David Meiland | | #2

    Agreed. Do your complete rough-in now.

  3. Jesse Smith | | #3

    Not sure where you are in the process, but my company installs a fair bit of 3"-5" EPS on basement and crawlspace walls, which generally requires an ignition barrier. Partly because of the thermal bridging problem Robert mentions above, we quickly got away from fastening through the foam . Our current solution is to glue 20 gauge steel to the foam, and attach drywall or plywood directly to the furring strips. I probably wouldn't recommend it for a highly finished space, but for a utility grade space it will work fine. If you have access to metal brake you can really speed things up by creating a 2" 'L' at the top of each piece of metal. Make certain your adhesive is compatible with both foam and metal.

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