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Community and Q&A

Reclaimed polyiso that has been exposed to weather

Jaero | Posted in General Questions on

I’ve been looking around for sources of reclaimed insulation.  I found a listing on my local Craigslist with the attached photos.  1 1/2″ thick 4×8 sheets of used polyiso for $15 a sheet.  I am considering buying enough for 2 layers of interior insulation on my basement walls.

Should I be concerned that it has been stacked and stored outside, apparently uncovered, exposed to the weather?

The listing doesn’t say (and I haven’t called yet), but these appear to have a black felt coating.  If it is felt coated, is exposure to weather a bigger concern?

More general question… Is felt coated OK to use as basement insulation?


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  1. Expert Member
    Dana Dorsett | | #1

    Weigh a sheet of it., or maybe two. A 1.5" x 4' x 8' sheet is 4 cubic feet, and would/should weigh about 8lbs if bone-dry. If it's 10 lbs it means it's taken on some water (about a quart for the whole sheet) but it is not a disaster- it will (eventually) dry out in a basement wall application.

    Rain/dew wetted is one thing, pond-soaked is another. If it's 16lbs+ (a gallon or more per sheet) it's a wetter than I'd want to use. YMMV.

    A reclaimer near me was recently advertising sheets of 3" of known-soaked goods with sheets weighing north of 40lbs, (should be 15-16lbs if totally dry) and the ultra-low price reflected that.

    And yes, it's fine to use asphalted-felt faced foam on a basement wall. If the basement has a flooding history, stop the polyiso above the high tide mark. Even with no flooding history leave a gap between the cut bottom edge and the slab to prevent moisture wicking from a potentially damp slab.

    1. Jaero | | #2

      Thanks for the quick reply and density information. I hadn't thought about weighing it; I will take a scale along when I go to see it.

      The guy selling it will likely think I am nuts, but I have come to realize that I really am!


      1. Expert Member
        Dana Dorsett | | #3

        The guy selling it might already understand the issue- it's pretty common to have some pretty hefty sheets culled from old commercial & industrial roofs with chronic leaks. If it's news to him the education might prompt an investment in tarps (or even sheds).

        Almost all roofing polyiso is 2lbs per cubic foot nominal density, but there are both lighter and denser versions. For 4x8 sheets they should run approximately 2lbs x thickness" x 2.67 = lbs/sheet, give or take. The (rarely seen at reclaimers) denser versions are usually 4lbs, and noticeably stiffer, harder, more difficult to dent, often sold in 4x4' sheets and 1-1.5" thicknesses.

  2. dfvellone | | #4

    I bought quite a bit of 3'x4'x3" sheets a year and a half ago that I soon discovered had a good percentage of sheets that weighed considerably more than others. When I ripped them on the table saw I found that they were waterlogged, some more than others. A year and a half later and they're still waterlogged after having been stored inside. Didn't seem to matter how they were stacked or how much warm air flow I provided. They are 3" thick and that may well impede drying. I'd be wary of polyiso stacked outside. The last thing you want is to end up with a pile of it that you have to get rid of.

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