Compressive Strength of XPS for Steel Building
I will try to keep this brief, but I wanted to explain a bit of the process in hopes it may help someone else, or someone can poke holes in the design.
I am in the process of building a steel building. The building has steel girts and purlins. I wanted to do something to remove the thermal bridge between the outside metal panels, and the steel girts. To do so, I want to sheath the building with 1″ foam board and then put the metal paneling on top. To achieve this with less hassle, I am planning on building “foam panels”. I found some second-hand house wrap, so i plan to lay the wrap down, then (lightly) glue 4×8 sheets of foam down to the house wrap, sealing each joint between boards, making an 8′ wide panel the exact height needed for a wall (18′ in this case). I can the set the panel up against the wall, put up some temporary support, and then screw wall panels on top. I will leave house wrap on either side of the panel to allow overlap with the next panel. After the panels have been assembled, I can go back from the inside and seal between the panels with can foam.
Next, i wanted to do something similar with the roof. I figured it may be beneficial to go with something a little thicker, so I decided I would do the same thing only use 2 layers of 1″ foam, staggering the joints in my “panels”.
Finally, (but chronologically, first), I have made glued 2′ tall 16′ long panels out of 2 layers of reclaimed 1″ foam to insulate the buildings footing/stem wall (I am not putting foam under the floor, just insulating the perimeter with 2″ foam).
Everything I have done has been with Foamular 150 (15PSI) insulation so far. However, I got to thinking, will this lower compressive strength foam be a problem in any of these applications?
In my head, it seems that I don’t need a ton of compressive strength for the walls of the workshop. Guys regularly use those rolls of fiberglass batts and double bubble, both of which I consider “squishy”. I am hoping the 15PSI foam works better without oil canning the panels.
The foundation lining seemed okay as it is not underneath any of the load bearing surfaces, it simply lines the sides of the foundation. Documentation online seemed to make me thinking 15PSI was sufficient.
Perhaps my bigger concern, is the roof. Is 15PSI foam okay for this application? Keep in mind, the foam panels will sit directly on the purlins, then the metal panels on top. Do I need to put some kind of support board in my panels to sit against the purlins and distribute the load?
I’d be interested to hear peoples perspective on this plan.
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