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Community and Q&A

Downside of Reclaimed Polyiso Rigid Foam

okapi222 | Posted in Green Products and Materials on

We are thinking of using reclaimed polyiso rigid board on a roof exterior. What are the downsides of doing this? Can anyone come up with an argument against it?

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  1. PAUL KUENN | | #1

    If it's been on a roof for 20+ years I'm sure it's lost a bit of the R value (I figure 1-2 per inch) but I use it all the time. I do cap it with EPS though to keep it warmer as Polyiso does lose a lot of R value in colder weather.

  2. Expert Member
    BILL WICHERS | | #2

    The biggest downside is usually that there will be some chunks out around the edges of the polyiso sheets. I just fill them with canned foam when needed, so it's not a big deal. Sometimes there will be cutouts (this is usually noted by the reclaimers though), and holes from fasteners. Having the the holes line up with where you need you fasteners to go is even less likely than winning the Powerball, but the holes are small and don't really matter so they aren't a big deal either.

    Those are the downsides. Sure, it's aged a bit as Paul mentioned, but think of it as "stabilized at it's long-term R value", which sounds a lot better than "lost a bit of R value", and then that's not a big deal either :-)

    The big advantage is you save a lot of moneym and you're using reclaimed material so you have a greener option compared with buying new. I personally love when I can reuse something in a useful way rather than seeing it go in the trash.

    I don't really see a downside. Reclaimed polyiso is best in places where it will be hidden (crawl space walls, roofs, behind siding), since no one will ever see the downsides of the slightly rougher looking sheets that way. I think you have nearly only upside to using reclaimed polyiso for your project.


  3. brian_wiley | | #3

    I'm looking at reclaimed polyiso as well, and one thing I came across was that it can absorb quite a bit of water depending on how it is stored. I don't have any direct experience with that though, and that may not be an issue if you have the ability to inspect it first.

    edit: here's an post that mentions the concern in question, along with how to address those concerns:

  4. Expert Member
    Akos | | #4

    Make sure to give the polyiso a good sniff. Stuff that has been exposed to water can sometimes smell like @#$ and the smell won't dissipate for a very long time.

  5. Mifranc58 | | #5

    To not have odor problem, the kind of polyiso to reuse is the polyiso which is cover with a a fiberglass and acrylic facer, not the one with an organic facer. Also don't exceed a thickness of 2'', until 2'' the polyiso is permeable to the vapor and with a polyiso with a fiberglass facer coated with acrylic, the surface is waterproof.

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