MULE-HIDE POLY ISO2
Josh24
| Posted in Building Code Questions on
Per the 2018 IRC, can “MULE-HIDE POLY ISO2” be used below a slab on grade?
My supplier says I can, but have read mixed reviews on it. I’m not really looking for more opinions on it, just will it pass code. Thanks!
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Replies
Josh24,
"Polyiso, however, should not be used under slabs or in contact with soil because it will absorb groundwater over time, resulting in lower performance."
Source: https://www.greenbuildingadvisor.com/article/the-best-way-to-insulate-a-foundation
That datasheet seems to only talk about using this product on a roof, not under a slab. Polyiso itself can't be used under a slab because it will take on moisture, basically it acts like a sponge. You don't want water logged insulation since it won't insulate anymore! Even if the polyiso was completely encapsulated (and that product doesn't say that it is), if you got ANY punctures or tears in the outer jacket, you'd end up with water getting in and wrecking the insulation.
Polyiso really isn't suited to any below-grade applications (note that that doesn't mean inside a basement where it's below the level of the ground, but still on a wall exposed to air). You should stick with one of the recommended foam types (XPS or EPS) for subslab insulation.
Bill