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Community and Q&A

Metal over exterior rigid insulation?

mcookarch | Posted in General Questions on

Hi all, I am an architect working with a private client on a farm structure in a cold-weather climate (many feet of snow accumulation during the winter months). I am trying to determine how we can utilize rigid insulation on the exterior of the foundation wall and finish it in a way that will protect the insulation, will stand up to nearby heavy-duty farm work, will not require ongoing maintenance as a result of freeze/thaw cycles, and will look attractive at any distance. I would also prefer a finish material than I can run below grade so as to eliminate the visual discontinuity that comes with ending a parge coat or other cementitious applied finish several inches above grade.

I have seen builders on this site recommend using a metal product, such as aluminum coil stock, as both a protective material and finish for this detail at the top of the foundation wall. However, I am having a difficult time selling my team on this idea and am also having a tough time finding images of metal-over-rigid online. I am hoping to crowdsource as many photos of this finish as possible. I am fairly certain it is a viable option for us, but I think our team is struggling with visualizing how it will work with our material palette (standing seam metal roof, dark blue Hardie siding). This is a fairly deluxe project, so photos of materials that may not work on a more conventional project (even something terne-coated, stainless, or copper) are also very helpful. The key is that the material should be resilient and attractive, not necessarily the most budget-friendly option. If you have other suggestions for a material that might work at this location in place of a metal finish, please let me know, keeping in mind our aesthetic requirements. Thanks very much for your help.

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  1. ERIC WHETZEL | | #1

    We struggled with the same area on our build last year.

    We intended to use a cement board with a parge coating, but we couldn't find long enough flat-head concrete screws to sufficiently penetrate 5" of Rockwool and the concrete of the foundation.

    Instead, we reluctantly went with metal flashing, essentially just continuing what would've ordinarily been Z-flashing from the Zip sheathing down over the face of the Rockwool on the foundation. We then combined this metal flashing on the exposed portion of the foundation with a washed gravel border around the perimeter of the house (covering the termination point of the metal flashing over the Rockwool).

    I was expecting it to be a pretty mediocre looking compromise, but we've ended up very happy with it. It helps, too, that for most areas around the house actual exposure is less than a foot tall. The one exception to this is on our west facade, but even where it's more fully exposed it looks good to us, and it's held up fine so far.

    I'll attach a couple of photos, including the west facade.

    When people have visited the job site, now completed house, they ask a lot of questions, but no one even seems to notice this area, in part probably because the metal matches the siding color so it blends in well.

    This seems to be an area of "green building" that continues to perplex people (someone contacted me through my blog just yesterday asking about this exposed above-grade area), probably because there don't seem to be that many options, and none of them seem all that ideal.

    Based on what I've read, including here on GBA, it's a choice between concrete board/parge coating, metal flashing, or some kind of pressure treated wood.

    Maybe someone else here on GBA has heard of, or even tried, other options?

    1. mcookarch | | #4

      Appreciate the reply and advice, Eric. This is essentially the solution I am proposing our team investigate, and I think it blends very well with the siding on your project. Your photos are additionally relevant to what we're doing, as we are planning to run a gravel drainage strip around the building perimeter.

      As you said, the options seem to come down to concrete board, metal flashing, or PT wood. I am concerned about long-term maintenance challenges RE: snow build-up with the former, and aesthetic issues with the latter, as well as potential for water damage/rot if anything goes wrong with the product or install. Which sort of leaves metal, as far as I can tell...

      Thanks again for your feedback and images.

  2. Jon_R | | #2

    I've had no problems with surface-bonding fiber reinforced cement/stucco direct to foam, even with it extending to just below the surface (gravel) in a cold climate.

    For maximum durability (at a cost), I'd consider brick.

    1. mcookarch | | #3

      Thanks for your reply, Jon. One thing I should have noted in my original post: while I agree that brick would be ideal at this location, we are intentionally staying away from masonry to simplify our foundation and to match materials used elsewhere on site (we do not have masonry at the water table on any other building). It would also be a bit unusual for a barn structure, though you are right that this option would certainly have the best potential for durability and resiliency.

  3. Expert Member


    Probably the best looking solution for a semi-industrial look in an agricultural building would be corrugated or standing-seam panels. The problem is that even if pre-finished, they both start with a galvanized base which won't do well over time if buried below grade.

    I'd suggest getting a fabricator to bend seams into pre-finished aluminium stock at regular intervals (say 2'-0"?). This would both help reduce oil-canning and might better fit in with the rest of the building the using straight stock.

    1. mcookarch | | #6

      Malcolm, this is solid advice. My primary concern going with an aluminum product at this location has been oil canning over time and wasn't sure how we might mitigate it. This is a good solution.

  4. Seabornman | | #7

    I used two coats of an acrylic-cement coating (Tuff II) over self-adhered fiber reinforcing mesh. It makes a very durable and flexible finish.

    1. mcookarch | | #8

      Thanks for your reply, Joel. Will Tuff II stand up to repeat freeze/thaw cycles and snow build-up over the winter? Their site does say you can run it right to (and even below) the grade line, which is what we're looking for.

  5. thrifttrust | | #9

    I used Tuff II on my house in Traverse City, MI (CZ6) 7 years ago and I it has held up well, and I think it has aged well. I took it below grade and around the 4' deep basement egress window. I parged it over XPS onto which I had abraded bullnose corners. On the window sills and areas of concern I used a second layer of fiberglass mesh over two coats, followed by a top coat of Tuff II. Freezing seems to have no effect. That said, the soil is essentially beach sand and it drains very well.

    Obviously any thin parging over foam is subject to damage (as would thin guage metal) but it is easy to patch and repair.

    Douglas Higden

    1. mcookarch | | #10

      Douglas, thanks very much for your response. I have now had Tuff II recommended several times, but was still concerned about how it would do below grade and in snow, so am reassured by your experience using it without issue. Thanks.

  6. GBA Editor
    Martin Holladay | | #11

    M. Cook,
    You might want to see the photos accompanying this article: "A Superinsulated House from 1984." (Look at the lead photo, as well as some of the photos in the photo gallery.)

    The owner-builder went with stainless steel.

  7. user-7022518 | | #12

    What about Boral--it is approved for ground contact:


    1. Expert Member
      Michael Maines | | #14

      Good tip, Lisa. Boral has promised to release a sheet-type product at some point, which will make using their product easier for taller foundations, at a lower cost than using their 3/4" material.

  8. Expert Member
    Michael Maines | | #13

    MCook, search Google for "GO Logic". They get a lot of projects published, and routinely use stainless steel sheets to cover the insulation on their foundation system.

    I'm not a fan of the look, and usually try to design the insulation to go on the interior instead. But when I have to use exterior insulation or ICF forms, I spec one of these parge/stucco systems:

  9. Seabornman | | #15

    This is my first winter with the Tuff-II in place so can't comment on freeze-thaw. I also applied to XPS and extended 6" or more below grade. I have hit it with string trimmer with no effect. I might add that it bridges various materials fairly well. BTW, if you plan to use Tuff-II, follow the instructions re: not applying in direct sun. It sets up very quickly on even a mild day in direct sunlight.

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