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Reclaimed and factory second rigid foam

user-6789598 | Posted in Green Products and Materials on

I have seen a couple of recommendations here and there on obtaining reclaimed rigid foam. One post actually mentioned the Syracuse area, close to where I live, so I checked craigslist as they suggested and sure enough there was–new, reclaimed and factory second rigid foam.

If appropriate, it would be used on new construction in the Finger lakes region, under and on the below grade walls of a full basement. Possibly under a garage slab, but I am not sure how necessary rigid foam is under a garage slab because it is a topic I have not thought to research until 5 seconds ago. From what I learned reading other posts, I would need 4″ rigid foam for under the slab, can’t remember how to determine what I would need for the walls, but I’m sure I have read it somewhere on here.

Q1: Would reclaimed or factory second rigid foam be a reasonable solution for a basement slab and exterior walls based on the description above?

Q2: What are the cons of using reclaimed or factory seconds?

Q3: What should one be looking for when they inspect the foam prior to purchase?

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  1. GBA Editor
    Martin Holladay | | #1

    There are at least two issues here.

    Issue 1 concerns choosing the right type of rigid foam for a particular purpose from among the three major types of rigid foam: polyisocyanurate, EPS, and XPS. For more information on this topic, see Choosing Rigid Foam. If you follow the advice in that article, you will avoid blunders like installing polyiso under a concrete slab.

    Issue 2 concerns whether the quality of recycled rigid foam is high enough to make it usable. The simple answer is yes. The quality of shipments varies; ask the seller a few questions (or inspect the foam) to determine how many pieces have broken corners. You can always order 10% or 20% extra and choose the best pieces; you'll still come out ahead.

    The only difficulty I have heard about concerns irregular thickness of reclaimed polyiso. Inspecting the rigid foam before purchase, or a little bit of on-site sorting, will usually solve this problem.

    -- Martin Holladay

  2. STEPHEN SHEEHY | | #2

    Nina: We put 4" of recycled xps under our slab. The foam was a little dirty, but otherwise perfect. I had ordered a little extra in case we had some unusable pieces, but it was all fine. I had a few sheets left over and put them under one end of the garage slab where someday I might frame a work area. If you might ever heat the garage, putting foam under the slab is probably worthwhile.

  3. Dana1 | | #3

    Only polystyrene (EPS or XPS- either is fine) can go under the slab or on the exterior of foundation walls) but polyisocyanurate (with any type of facer) is fine for foundation walls, as long as you keep the cut edge at the bottom from resting on a slab or dirt, since it can slowly wick ground moisture and lose some performance.

    Reclaimed foam may have changed a bit from it's initial nominal dimensions- a 4'x 8' sheet of XPS might measure as short as 47.5" x 95" if it's been in service for 20 years, and the nominal thickness can vary a bit too, but those issues are usually only problematic when doing triple layers.

    The R-value of used XPS can be less than virgin stock, since it's initially higher R-value is dependent upon it's blowing agents, which can leak out over time (more of an issue with HFC-blown goods than pre-Montreal CHFC blown foam), so from a design point of view assume it's fully-depleted value of about R4.2 per inch. ( EPS loses it's blowing agents early in life, and is usually labeled at it's fully depleted R4.2/inch.) Also, 2lb density roofing polyiso has a slightly lower R than the foil-faces 1-1.5lb goods, so derate it to R5/inch - R5.5/inch for design purposes.

  4. user-6789598 | | #4

    Loss of R value in reclaimed foam was not something I had thought of; definitely a criteria for decision making. Thank you gentlemen for the insights. I can not even begin to verbalize the benefits of your articles, blogs and Q/A section. I have been in at least 4 conversations (phone or face to face) this week alone regarding our project, where I am more actively part of the discussion, and it is amazing how much more valuable information comes out from the contractor when he/she realizes that I have even a rudimentary level of understanding of the concepts and terms. Thanks again.

  5. GBA Editor
    Martin Holladay | | #5

    The loss of R-value that Dana Dorsett is talking about is called "thermal drift." It occurs with XPS and polyiso, and it occurs regardless of whether the foam is purchased new or is purchased used.

    For more information on thermal drift, see Thermal Drift of Polyiso and XPS.

    -- Martin Holladay

  6. Jon_R | | #6

    Multiple layers with staggered seams is preferable. Even more so if there is some damage.

  7. charlie_sullivan | | #7

    I think that the shrinkage is an advantage of using reclaimed foam. It's better put it in pre-shrunk than to have it shrink in place and leave gaps.

    The main reason I wish I had foam under my garage slab is that it would allow the slab to warm closer to air temperature in the summer, reducing the risk of condensation on the slab and generally allowing the garage to have lower humidity in the summer, resulting in less chance of mold and rusty tools.

    But another reason is to reduce risk of the ground freezing under the slab and cracking it if it gets very cold in the garage.

  8. user-6789598 | | #8

    Thank you for the clarification and assistance.

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