GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Who sells magic rigid foam insulation that is also usable as structural sheathing?

LX2xNRcGsd | Posted in General Questions on

I am a licensed Architect in the Seattle area. Why is it that so very many of the DWG details particularly wall sections, fail to show or call out the structural sheathing? What kind of magic rigid insulation do you use and where do I get it?

Seriously, please Send me an email at
[email protected] from a email address where the mail is picked up by someone

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. vQpreEBoVw | | #1

    Dow SIS board comes in 1/2" & 1" thickness & should be available through most lumber yards . It's not magic , but it is structural .

  2. user-869687 | | #2


    On the west coast you will not easily escape using plywood sheathing for lateral loads on a conventional wood frame building. In some areas it's sufficient to use let-in 1x bracing, steel T-bars or thin fiber board (Thermoply) under foam sheathing. Or, the mysterious SIS, which may be a higher density plastic. Sadly your engineer will not agree to this in Seattle.

    With light gauge steel framing it's possible to use diagonal flat straps and foam sheathing, but that's only because the straps can be welded to HSS corner posts. Wood framing in seismic areas (or near a windy coast) will generally require full coverage plywood sheathing and lots of nails.

    Speaking of light gauge steel, there is a panel made with drywall laminated to 22 gauge sheet metal, which could go at the interior and replace exterior shear panels. I forget the brand but they also sell a thin (1/8") panel with sheet metal over MDF, to install behind regular drywall.

    Or, you could handle lateral loads with interior concrete shear walls, as is typical in high-rise construction with non-structural curtain walls. Interior shear walls could even be plywood and frame, but this will require engineering.

  3. user-869687 | | #3

    This is the aforementioned sheet metal shear panel: Of course it would be unwise to install sheet metal on one side of a frame and foam sheathing on the other, as there would be no possibility of drying. You could add add this under foam sheathing, and if the lateral loads were light it may be sufficient to only brace certain areas of the wall.

  4. LX2xNRcGsd | | #4

    Thanks, knowledge is power!

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |