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Community and Q&A

Insulating Steel Columns in a Basement

Brian M | Posted in Energy Efficiency and Durability on


I am starting a project to frame and finish my basement with 2×4, 2″ XPS foam board in zone 5. I am trying to plan on how I will insulate the support I-beams that one wall has previously had installed.

There is essentially no gap between the beam and the concrete so I’m thinking the only solution is to go around the beams with the XPS board I have or to put the board on the concrete wall and use some kind of spray foam on the beams with the spray foam meeting the boards.

I’m also curious if anyone  has recommendations on if I should add batts of insulation in addition to the 2″ XPS.

Any suggestions? I attached images to illustrate this.

Appreciate you guys

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  1. Expert Member
    Michael Maines | | #1

    Brian, beams are horizontal members; you are showing a column. The only option I can think of is to wrap it in insulation. Builders who care about their environmental impact don't use new XPS, as it has extremely high levels of embodied carbon (i.e., major greenhouse gasses) compared to nearly any other option. EPS or polyiso would be just as effective and more environmentally friendly.

    1. Brian M | | #2

      Thanks for the info Michael. So stay away from XPS, got it! Do you have any suggestions on what product would be best to wrap the columns in?

      1. Expert Member
        Michael Maines | | #4

        Brian, for basement interiors I use polyiso, which has a high R/in, is vapor-impermeable if it has foil facers, and has relatively low global warming potential compared to other foam options. There is some debate whether foundation walls should be able to dry to the interior but as long as the exterior, above-grade portion can dry to the exterior, I prefer to block drying to the interior. Thermax brand polyiso has gone through testing to allow it to remain exposed on the interior, and it's available with white foil facing, which makes a nice semi-finished interior if you aren't fully finishing the space.

        Alternatively, you can use EPS, GPS or recycled XPS. As long as you have enough foam to control the dewpoint location, you can add a framed wall with fibrous insulation on the interior.

    2. Patrick OSullivan | | #6

      But! Sometimes those members are used to stabilize bowing foundation walls, and I have heard them referred to as "wall beams" in that application. The CMU cracking near that piece of steel makes me wonder if that's actually what it's there for!

      1. Brian M | | #7

        You are correct, I believe these beams/columns were installed by the previous owner to support the foundation wall.

    3. Will R | | #8

      Michael, this has changed recently, correct? Blowing agents have improved for xps on 3 of the big brands.

      1. Expert Member
        Michael Maines | | #9

        Will, yes, the blowing agents in some formulations of XPS have improved, reducing XPS's global warming impact by roughly 25%--still worse on a carbon emission per R value basis than any of the other options.

        1. Will R | | #10

          Thanks I didn’t realize it was still more than the others. Good to know.

  2. Expert Member
    Zephyr7 | | #3

    I would box over the column with polyiso. I'd probably use Dow Thermax here (or Johns Manville's equivalent), since it doesn't need a thermal barrier (drywall) over it, and with a column I'd want to keep the dimensions as small as possible.

    BTW, I would make sure the column's paint is in good shape before boxing it over. If you find any loose paint, use some Rustoleum "Rusty Metal Primer" on it, and ideally a top coat of one of the "stops rust" enamels too. Once you box that column over, it will likely see higher moisture levels, so it's prudent to make sure it's well protected against rust.


    1. Brian M | | #5

      Thank you Bill, I really appreciate the columns rust advice. That never crossed my mind.

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