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Using recycled rigid foam

user-2310254 | Posted in Green Products and Materials on

I’m considering using rigid foam on the exterior of my roof. Cost is of course a big concern with this approach. I’m found sites online that sell recycled rigid foam. Apparently, it is often recovered from commercial buildings and shipping containers.

I read one post on the site that caution against using foam that had been degrade during freeze/thaw cycles. Are there any other issues to look out for? Have anyone tried the “recycled” approach? Is there a reputable source for material? Any lessons learned you folks could share would be greatly appreciated.

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  1. Expert Member
    Dana Dorsett | | #1

    While it's possible to get freeze-damaged goods, most reclaimers cull the true junk from the pile. has a decent rep, as do some of the other southern New England factory-seconds and reclaimed foam vendors.

    A deep energy retrofit I was involved with last year used primarily reclaimed roofing iso, (3-4" on the walls, 6" on the roof) and the scrap rate due to quality issues with the foam was essentially nil.

    On a basement retrofit insulation project I did 4 years ago out of ~40 3" x 4' x 8' sheets, only one had what appeared to be freeze/thaw damage, one or two others had fully cracked under the facers (mechanical stress, not freeze damage), others had a few dings & chunks taken out, but the scrap rate was still under 10%. (Some of the damaged pieces were used to cut'n'cobble insulate the band joists and foundation sills.)

    So while there's an incoming inspection and sorting issue to deal with, but it's still usually worth it.

  2. user-757117 | | #2

    99% of the rigid foam I used in my own home was recycled.
    I got it from someone locally and was able to inspect it at his warehouse before I paid for it.

    You can expect that recycled foam will be a little beat up (fastener holes, dings and dents, etc) but that doesn't matter much.
    One thing to watch out for - foam boards that seem unusually heavy are probably water laden.

    My observations agree with Dana's, the percentage of unuseable material in what was delivered to me was very low.

  3. ohioandy | | #3

    My LEED build got off to a rough start this week when I discovered the foundation contractor using XPS foam to form the brick ledges. Essentially, for him it was a quick (if not cheap) way to displace concrete in the forms. His plan for the foam after stripping? "Throw it in the dumpster."

    No dumpster on my site. My plan now is to use the scraps to insulate the rim joist areas between floors, with expanding foam to seal and hold in place. It's virgin foam, except for the concrete residue and nail holes.

    Note to self: ask more questions.

  4. user-2310254 | | #4

    Thanks for the great input. Dana, InsulationDepot is a great lead. It looks like XPS is my best option for insulating the outside of a roof assembly. But there seems to be quite a range for XPS r-value. To get to r-38, which I need for Zone 3, I might need something like 10 inches of foam. Does that sound right?

    I'm also been debating how to insulate the basement. I'll probably have two walls that are largely below grade. Again, it looks like XPS would be the way to go, but I only need to reach r-10. Of course, you have to be concerned about termites and carpenter ants in our climate. I know I could put the foam on the inside but am not wild about introducing more flame retardant into my structure. Any thoughts on this issue would be welcome.

  5. Expert Member
    Dana Dorsett | | #5

    Polyiso is somewhat better for insulating roofs, especially when looking at reclaimed/aged XPS. After 50+ years the R/inch of XPS is about R4.2/inch (just like EPS), but roofing iso will still be running ~R5.5/inch or better forever, though it started out at R6-R7 early in it's lifecycle.

    For zone-3 they usually allow R30 for cathedralized ceilings, and that's presumed to be center-cavity between rafters. When applied as continuous insulation above the roof deck you can go lower still and still hit the same performance, due to the much lower thermal bridging when you have no framing cutting through the insulation layers. When new XPS runs about R5/inch and you'd be able to hit R38 with 8" of foam, R30 with 6". Using staggered layers or 3" iso (6" total) gets you there with margin to spare.

    Alternatively it's perfectly fine to split the R between above & below the deck, as long as you use at least the IRC prescribed minimums for the above the deck fraction:

    In zone 3 you can get away with a paltry R5 above the roof deck, but if you put say, two staggered layers of 2" foam (R22+ if iso, R17 if EPS), then you'd beat code with standard R23 rock wool or high-density fiberglass batts, or a full-cavity blown-fiber fill between the rafters.

    In the basement you can use iso on the interior as long as you keep the bottom edge off the slab. On the exterior you could use either XPS or EPS, but would have the insect tunneling issues. Roxul Drainboard high-density rock wool panels would get you there with lower insect potential, but at a huge cost uptick over reclaimed roofing EPS. To insulate from the interior you could put as little as 1/2" of foil faced iso or XPS between the foundation and a studwall, and insulate the studwall with unfaced rock wool or fiberglass and meet your R10 code min with a minimum of fire retardent.

    Alternatively, a single layer of 2" roofing iso held in place with 1x furring through-screwed to the foundation on which you hang the gypsum works, and works well. (I did mine with 3" of roofing iso + furring.) Foam-seal the seams & edges with can-foam, leave yourself an air gap between the foam & slab as a capillary break to keep the iso from taking on ground moisture. Unlike EPS and XPS, iso does not melt even when burning, and it's much harder to light-off. It still requires an ignition barrier (like 1/2" gypsum), but it's a lower-risk material than polystyrene from a fire point of view.

  6. user-2310254 | | #6

    Thanks, Dana.

    Does it matter if the polyiso has a foil facing? On the R-value, it seems you're saying that code assume that there will be thermal bridging. If you eliminate the bridging, you can meet code with less R-value. Is that correct?

  7. Expert Member
    Dana Dorsett | | #7

    Foil facers aren't needed but also aren't a problem for above-deck roof insulation.

    Codes for attic R presume some amount of thermal bridging, and are a center-joist number. Most locales that have R38 for joist insulation allow R30 for rafter insulation, in part due to a presumed 24" o.c. rafter spacing (= lower framing fraction) as compared to 16" o.c. presumed attic floor joists. SFAIK there is no equivalent prescriptive stackups in the IRC for meeting code the way there are for walls. R20 cavity fill or R13 + R5 continuous sheathing are considered equivalent for wall-R in the IRC prescriptions, but they don't make similar equivalency-prescriptions for unvented insulated roofs, only the min-exterior R.

  8. rondog56 | | #8

    Another good source for reclaimed, recycled, or factory seconds is Green Insulation Group

  9. claythonmclaw | | #9

    I know I'm late to the thread, but what kind of canned foam would be suitable for repairing imperfections in recycled polyiso insulation (fiber or paper faced)? I'd imagine something like polyurethane would expand too much. While I plan to tape the seams, of course I don't expect that the foam boards themselves will be perfect.


  10. bdrfab | | #10

    I used great stuff. just trim squeeze out afterwards. The gun has much better bead control than individual cans, but it is an additional upfront cost

  11. PAUL KUENN | | #11

    Hey Steve!

    I've found house's worth of used foam on Craig's list locally. Especially in spring when contractors want to empty the storage sheds. Just search insulation foam under "Materials" and it's almost always with a photo or two. And much less than the recycled suppliers. You just may need a trailer.

  12. peaceonearth | | #12

    Spray foaming - if you plan on doing any amount of it a gun is well worthwhile. They start at around $50. The cans and the straw applicator are awful to use. With a gun you can also buy larger cans (obviously one HAS to buy gun compatible cans) at box stores and elsewhere much cheaper per ounce than non-gun cans. Its also much easier to maintain a partially used can for reuse with a gun.

  13. agurkas | | #13

    I bought a mid-level gun for the foam and I am never going back to non-pro cans. The level of control and ability to stop in the middle of the job and come back up to 30 days later is worth the relatively minor price.
    Also I find that you can get at least twice as much foamed with the gun. Much much less waste.

  14. peaceonearth | | #14

    Foam gun FYI. I have a standard gun but after using for some time I often wish I had gotten one with a longer applicator. I've seen a 28" one for about $85 and a 40" one for $105. If you do much foaming around the house over a period of time in different locations you will find this extremely helpful and sometimes even essential. There were places, especially for rim joists that could not be reached adequately with the standard gun.

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