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Community and Q&A

Using Reclaimed Fiberglass (?) Faced Polyiso

rob kohaus | Posted in General Questions on

I have access to some 3.5″ reclaimed polyiso that I believe has a fiberglass facing on each side of the board. At least, I think its fiberglass. The best way to describe the facing is it kind of reminds me of landscape fabric.

My intention was to use the foam as sheathing on the walls of the house I’m building. I am just down the road from Urbana, IL (Climate Zone 5A….but feeling a bit more like 4A at times).

My wall assembly (from interior to exterior) is as follows…..
– drywall
– 2×6 with mineral wool batts (R-23)
– ZIP sheathing
– 3.5″ polyiso (~R-22)
– cladding (combination of air gap w/ stacked limestone veneer and EIFS)

My questions are…
1.) Am I right that this is probably fiberglass facing on the polyiso? I’m new at this and have seen felt faced and foil faced, but not fiberglass faced. (my guess is I’m right)
2.) Will the facing (whether its fiberglass or not) on the polyiso in any way effect my ability to use the foam for its intended purpose? (my guess is no)
3.) Martin, I read your blog “Return to the Backyard Tape Test.” If I can use the reclaimed polyiso and it is indeed faced with fiberglass, any suggestions for a good tape to use at the seams? (my guess is something that was tenacious on the house wrap will work well on this facing…)

Thanks in advance!

– Rob

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  1. GBA Editor
    Martin Holladay | | #1

    I can't answer your question about the facing, since I don't know what you have. Roofing polyiso is available with a variety of facings. All I can tell you is that polyiso is, indeed, manufactured with fiberglass facing. I'll attach a photo of one such product (Firestone ISO 95+).

    The facing won't cause any problems with your wall. The biggest problem encountered by builders who use recycled polyiso on walls is that the foam often has an inconsistent thickness.

    I haven't conducted any tests of tapes on recycled roofing foam. My guess is that it may be tough to tape. It's hard to beat Siga Wigluv as a tape for difficult substrates, and Wigluv would probably work better than other tapes.


  2. davidmeiland | | #2

    Does anyone have perm rating info for 2" fiberglass-faced polyiso?

  3. scottcmccullough | | #3

    We used reclaimed polyiso rigid insulation to insulate our roof and walls in our home that we recently completed. It had a paper facing with fiberglass in it which sounds like what you're looking at using. It is not intended to be used in any damp locations so I would not recommend it as part of any rainscreen system. When it gets wet it warps and the facing kind of falls apart. It should be located behind the exterior sheathing and kept dry. Also, I would not imagine that it would work well with any building tapes. The fiberglass facing frequently falls off and is generally not well adhered to the insulation itself. We did not find any thickness inconsistencies though that is something to look out for.

  4. GBA Editor
    Martin Holladay | | #4

    The Firestone product shown in the photo has a permeance of less than 1 perm, according to this document:

    Unfortunately, the manufacturer forgot to tell us the thickness of the product that was tested. Perhaps any thickness of this brand of polyiso has a permeance under 1 perm.

  5. GBA Editor
    Martin Holladay | | #5

    Thanks for sharing your experience and your advice about taping the seams. That is useful information.

    I disagree that "It should be located behind the exterior sheathing and kept dry." I think a layer of housewrap is all that is needed. So, from the studs out: sheathing, recycled polyiso, housewrap, furring strips, siding.

  6. rob kohaus | | #6

    Thanks for the quick responses everyone. Attached is a picture of the facing on the foam.

  7. rob kohaus | | #7

    Based on the picture Martin posted and the description provided by Scott, mine is probably something similar. The pieces (granted it was me eyeballing it) seemed to be in very good condition and consistent in dimension. I'm going to agree with Martin about the placement of the foam as well. Perhaps I will take a piece of the foam and try to saturate the facing with a hose and see how it handles a massive bulk water event.

    I tried peeling the facing off and it seemed generally well adhered. I say generally because I could peel it off in areas where it had already begun peeling. In places I tried where no peeling had occurred, the facing had a greater tendency to separate into layers than to peel off of the foam itself. Perhaps I will also experiment with some tapes and see how they do.

    Based on blogs and Q&A read here on GBA, it seems I could use certain foams as the WRB/"rainscreen system", but I was not intending to regardless of the facing. That was one of the reasons we decided to use ZIP sheathing. Martin, given our use of ZIP, do you still advise an additional WRB/house wrap over the foam? That would (almost0 be three barriers (housewrap, foam and ZIP).

  8. GBA Editor
    Martin Holladay | | #8

    In general, rigid foam behind a vented rainscreen is not a damp location; it is a dry location. So it's certainly possible to use Zip sheathing as your WRB if you want to.

    It's important to know where your WRB is located, because all of your window flashing and door flashing has to be intergrated with your WRB. Many builders would argue that it's easier to integrate your flashing with housewrap than with Zip sheathing, but either method is possible. Just be consistent, and remember where your WRB is located when you are planning your flashing details.

  9. Expert Member
    Dana Dorsett | | #9

    Without facers the permeance of polyiso is measured in 10s of perms. The facers are what controls the permeance of the sheet goods- the thickness of the polyiso foam itself does not make a measureable difference, whether it's 1 inch or 5 inches. The number and type of facers does.

    The fiberglass facers are typically between 0.5-1 perm, some asphalted paper facers are under 0.5 perms. Foil facers are in the sub-0.1 perm range. But it really would matter if it were 0.001 perms or 100 perms in your stackup- your foam/fiber R ratio is about 50/50 (OK call it 20/23), which has HUGE margin for dew point control at the ZIP sheathing layer in a zone 5A climate, for both winter & summer moisture drives.

    Facers on roofing iso aren't really designed for air-sealing with tapes. The most common application is under membrane type roofing, which is already air tight. For better air tightness you can add a layer of half-inch or 1" foil-faced goods on the exterior (seams staggered by a foot or more), and air seal the foil facer seams with FSK tape ( as was done on a deep energy retrofit I was involved with last year using copious quantities of reclaimed roofing iso.)

    (edited to explain) The reason I'm only allowing R20 for the 3.5" polyiso for the dewpoint control perspective is that it's 2lb roofing iso that's barely R6/inch @ 75F center-depth temp, and on the exterior side of R23 rock wool it'll be averaging under well under 40F center-depth at the outside temperatures that matter, a point at which you can expect ~R5.7/inch type performance from 2lb polyiso. Some 2lb & 3lb iso is only R5.5/inch @ 75F center-depth at it's fully aged performance, but most do somewhat better than that. The 1.5lb density foil faced stuff used as wall sheathing insulation is usually in the R6-6.5/inch range at 75F, but at 35Fcenter-depth it won't beat R6/inch.

  10. rob kohaus | | #10

    Thanks Dana and Martin for your contributions and sound advice.

    The "taping the seams" issue is one that has been bouncing around in my head. Is this done mostly for air tightness (as in the finished interior ACH type) or more to prevent moisture laden air from penetrating the seams and getting to the sheathing?

    If its more of an "ACH" thing.....Air tightness performance numbers on ZIP sheathed houses I've seen are usually very impressive. I've also asked three local drywall companies about Airtight Drywall Approach and not a single one had any idea what I was talking about. But one of them actually did a bit of homework and called me back and said they would give it a long as they weren't responsible for hitting any performance numbers. Better than nothing I guess.

    Dana - thanks for commenting on the HUGE margin for dew point control. I put a lot of time in researching and deciding on a wall assembly. I ultimately decided that this offered the best combination of cost, performance, embodied energy, recycled content, "greenness" and build-ability in my area.

    The house is Prairie style with stacked limestone up to a certain height (~3/4 way up the wall) then a ledge and then transitions to EIFS for the remaining 1/4. Every EIFS installer I've spoken with insists on putting 1" of their own foam on top of my 3.5" of iso.

    Given all the advice and my additional info about the cladding, would it be wise/necessary to install (as Dana suggests) an additional inch of foam in the "non-EIFS" section of the wall as well so the foam is all in one plane?

  11. GBA Editor
    Martin Holladay | | #11

    Q. "Would it be wise/necessary to install (as Dana suggests) an additional inch of foam in the "non-EIFS" section of the wall as well so the foam is all in one plane?"

    A. That's what I would do if I were you.

  12. Expert Member
    Dana Dorsett | | #12

    EIFS has no rainscreen gap, and you'd need something less hygroscopic to protect the polyiso from taking on moisture. An inch of EPS is probably necessary in the EIFS section, but you can use either foil faced iso or EPS elsewhere if you like. Stagger the seams with those of the iso.

  13. rob kohaus | | #13

    Thanks again guys.

    Sounds like maybe we should go with this assembly instead....
    - drywall (w/ attempted ADA)
    - 2x6 stud w/ rock wool
    - plywood or OSB (no ZIP)
    - 3.5" reclaimed roofing iso
    - 1" EPS or foil faced iso (staggered and taped seams)
    - house wrap

    All penetrations would be flashed to the house wrap. ZIP was switched out for regular OSB or plywood due to the WRB location(s) to save on cost.

    I think this would put a belt (housewrap) and suspenders (taped foam) WRB protecting the sheathing. There would now be an even larger margin of error for dew point control at the sheathing. And there would also be multiple air barriers.

    Does this all sound right?

  14. Expert Member
    Dana Dorsett | | #14

    Sounds good!

    BTW: A bead of can-foam or FrothPak between the edges of the polyiso as it goes up fills in most of the edge & corner dings and makes for a reasonable air seal (though imperfect), but requires trimming it flush before putting on the next foam layer. Whether it's worthwhile in your case depends on just how dinged up it is, and how straight the edges still are on the reclaimed iso.

  15. rossn1 | | #15

    Robert, if you're still getting notifications for this old thread, did you confirm if the polyiso shown above was coated glass fiber faced or paper faced? It looks similar to what I have available, which is shown in the below photo, and I want to use glass fiber faced, due to potential moisture issues. To me, it looks like a form of paper faced, but I really haven't seen different facers, except the foil.

  16. Dustin_7022224 | | #16

    Does anyone know about weather exposure with in progress construction for this (fiberglass faced polyiso)? We are using 2 layers of 2-1/2" polyiso over our roof sheathing and under a vented metal roof. I am first debating how quickly the metal roof needs to cover the polyiso and second if I should add a layer of synthetic roofing underlayment over the polyiso - my inclination is that the latter is overkill. FYI, we already have a peel & stick water and ice shield over the roof sheathing, which will sit right below the foam.

    1. Dustin_7022224 | | #17

      Answering my own question perhaps. I did just find this:

      Yes, it is still necessary to cover the insulation. The glass fiber reinforced felt used as the facer for most polyiso roof insulation should never be allowed to get wet whether from overnight rainfall or dew. The felt facer can and will absorb water, and it is never a good idea to trap it within the roof system. For more information, click the link below for PIMA Technical Bulletin 109 'Storage and Handling Recommendations for Polyiso Roof Insulation.'"
      with reference to this:

      1. Expert Member
        BILL WICHERS | | #18

        Some cheap poly sheet will make a good temporary weather barrier. Run some string over it to keep it down tight so that the wind doesn’t destroy it. You can buy 5,000 foot buckets of “pull string” at electrical supply houses that is perfect for this, and usually sound $50 per bucket. It’s a cheap, heavy parallel strand string about 1/8” in diameter that has very little stretch. You need to use enough string and keep it tight enough that the poly sheet can’t lift up and flap in the wind. As soon as you get that whipping action with the sheet flapping in the wind, it will start to work loose and tear.


      2. Expert Member
        Akos | | #19

        I always install underlayment over this type of polyiso on the roof. Doesn't matter if there is anything bellow it, the foam needs protection. This is cheap and much easier to walk on without damaging the foam.

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