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Are there any “green,” non-VOC spray foams?

Grey Wolf | Posted in Green Products and Materials on

I’m looking into doing closed cell spray foam for my floor, but the hazards really concern me.

I would like my insulation to be green as possible, without sacrificing quality.

I have read that even soy based (or alternative spray foams) are still quite harmful to breath. Is this true or are there any options that have been proven as a green alternative?

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    Properly installed, spray foam doesn't pose hazards for homeowners. (Installers of spray foam need to protect themselves during their work, however.) Once cured, properly installed spray foam is not (as you assert) "quite harmful to breathe."

    That said, there can be problems when spray foam isn't installed properly. These problems are rare but serious. To learn more about these rare situations, see Spray Foam Jobs With Lingering Odor Problems.

    The second issue you raise concerns "greenness." The main concern with closed-cell spray foam is the fact that most brands of closed-cell foam use a blowing agent that has a high global warming potential. For more information on this issue, see Avoiding the Global Warming Impact of Insulation.

    A few manufacturers of closed-cell spray foam are now offering products that are made with a more benign blowing agent. If you are concerned about the global warming potential of these blowing agents -- and you should be -- you should use either Lapolla Foam-Lok 2000-4G or Demilec Heatlok XT HFO. For more information on these new types of closed-cell spray foam, see Next Generation Spray Foams Trickle into the Market.

    -- Martin Holladay

  2. Charlie Sullivan | | #2

    Martin hit all the important nails right on the head, but I'll add that if you tell us more about your project, we can very likely suggest some alternatives that could achieve the same or better final performance or better at lower cost.

  3. User avatar
    Dana Dorsett | | #3

    I'm curious as to why anybody would even THINK of putting closed cell spray foam on a floor (do tell) !?!

    The "soy" content of "bio-based" foams is really but a fraction of just one of the two components that are mixed, and only amount to something like 15% of the total content of the product by weight. It's really just green-washing marketing BS. Where an application might call for closed cell foam selecting a product with a low-impact blowing agent would have far greater impact on the lifecycle environmental impact than the fraction of plant-sourced components of the polymer production.

  4. Grey Wolf | | #4

    Martin -

    I understand. Still, for me, that's just too big of a risk and I don't want to be concerned about that. The contribution to global warming is another big one for me. Polyiso is a potential option for me, but the foil gives me concerns about moisture (under subfloor).

    I have heard of these two spray foam suggestions. My understanding is that they still contain petroleum/ HFO's/flame retardants (but less of it), which doesn't really solve the problem for me. I will reach out to these companies to learn more about the ingredients, just haven't been able to yet. Do you know if there have been any tests examining the long term health affects? I doubt it since it's very new..

    What about about rigid foams? What are some greener options, without flame retardants (I know polyiso is probably the safest out of the big 3 but have my concerns that I mentioned above).


    You are absolutely right. I should of included this info! I will be building a tiny house on wheels (on a metal frame/bottom). I attached a photo of the trailer I will be using. I will be living in zone 3b (Southern California). My wall envelope will be a vapor open assembly (Roxul insulation) to allow drying exterior and interior...but the floor is a different situation because the bottom metal pan.

    I am very allergic to mold, so I am very focused on mold prevention.. but I also don't want to use the least harmful materials, without sacrificing quality.

    I would love to use roxul for the subfloor insulation as well but because it's vapor permeable and the joists are metal, I'm pretty sure I will want a closed-cell or vapor impermeable insulation for the floor.

    Do you have any suggestions to 1) Use roxul successfully without any moisture concerns or 2) The use of an alternative insulation this resistant to moisture does not grow mold?


    Exactly my point. The product seems to be slightly better but not near enough to persuade me to use it. Especially being in such a small spice (~200 sq ft).

    I do have a question to whomever wants to chime in:

    I recently discovered foamglas, which seems to be an amazing product (and I believe would work excellent for my subfloor insulation). What do you guys think? Does anyone know where I can buy this for a reasonable price? I have read on other Q&A's on here, that builders have been getting this product for under ~$1.50 per board ft...but I called some local companies carrying it and they quoted me $16 per square foot, for a 6 inch thick board. This would cost me over $3000 to insulate my (very small 8x28) floor. I would be able to budget ~$1500 but not $3000+

    Thank you all!

  5. User avatar GBA Editor
    Martin Holladay | | #5

    If you don't want to use spray foam, that's fine. Lots of builders agree with you on that topic. Use rigid foam instead.

    If you want to build a framed floor assembly, and fill the framing bays with mineral wool insulation, you can. The two disadvantages are: (1) It makes your tiny house taller, and (2) The floor assembly won't perform as well as one with a continuous layer of rigid foam in the floor assembly, because of thermal bridging through the floor joists.

    Foamglas has always been expensive, and it isn't being distributed anymore in the U.S. except for large commercial projects. For more information, see Foamglas Exits U.S. Residential Market.

    -- Martin Holladay

  6. Grey Wolf | | #6

    I'm not so concerned over the R Value because I will be in a warmer climate. I would much rather prioritize not letting water in and being airtight.

    So there will be no issues with the roxul in direct contact with the metal joists/floor? I suppose board would be better than batts. And I'm Not sure how I would lose height because it would still be 5 1/2" thick in the subfloor.

    Also, if any readers are interested, EJ Bartells carries Foamglas (and I can get some in 3 days) but it's quite expensive.

  7. User avatar GBA Editor
    Martin Holladay | | #7

    Q. "So there will be no issues with the Roxul in direct contact with the metal joists/floor?"

    A. If you have a flat steel deck, you can build on the deck. If you have exposed steel joists or structural members provided by the trailer company, you need to start with an OSB or plywood deck.

    In no case should you install steel floor joists. Use wood floor joists.

    -- Martin Holladay

  8. Grey Wolf | | #8


    The trailer has built in steel floor joists (see the posted picture above). There is no option to put a deck underneath the joists because they are attached to the sub floor.

    Because of this, I am thinking roxul won't be a good option.

    Do you have any experience with barriers/membranes that block voc's/off gassing? I have been researching such barriers, but I'm not sure if it would be suitable for me to lay over the joists (below my subfloor) to protect off-gassing from foam?

    Found something called: Protech VOC Flex

  9. User avatar GBA Editor
    Martin Holladay | | #9

    I'm not sure whether you are resistant to my advice, or whether you just have a hard time understanding basic construction vocabulary.

    The trailer in the photo has exposed steel joists. You don't want to put insulation between these joists or under these joists, because steel is a conductor.

    As I said in my very first response on this thread, you need to create a site-built SIP. That means that you start with a layer of OSB or plywood, on top of the steel joists. Next comes a layer of rigid foam. Then another layer of OSB or plywood. That's a site-built SIP.

    Once you have finished your site-built SIP, you can raise your walls.

    Even if you want to build a framed floor insulated with Roxul -- which you can do if you want -- you need to start with a layer of OSB or plywood on top of the existing steel joists. Then you can install your 2x4 or 2x6 floor joists, with Roxul in between, followed by your subfloor.

    -- Martin Holladay

  10. Grey Wolf | | #10


    I am not resistant to your advice. If that was the case, I wouldn't be asking questions. I understand the vocabulary, just was not understanding the wording. Now that you explained again, I now see what you are saying.

    I was simply asking for the best alternative solution to building a sip over the steel joists (because this tiny house calls to insulate in between the steel joists).

    I do understand it's a conductor and has more concerns with thermal bridging but it's what I have to work with.

    All of your advice is greatly appreciated and I am clear what your recommendation is.


  11. User avatar GBA Editor
    Martin Holladay | | #11

    You wrote, "This tiny house calls to insulate in between the steel joists."

    I don't know what person or article provided that advice. It is bad advice, so you should probably consider a different source of advice.

    -- Martin Holladay

  12. Grey Wolf | | #12

    Totally understand Martin. I'm trying to do my best not to pick and choose advice. Like I said, I very much respect your opinion and you are probably right: a site-built-sip, would be the best option for insulating my floor.

    Unfortunately, my home cannot lose any more height (13'6" max) or I would have to completely re-design the tiny house.

    With that being said, I'm going to make the best of what I have to work with. The good news is, that I will be in Southern California.. so R value is not as important as if I were up North.

    The trailer I am using, is by far the most popular for tiny homes so I am hoping I can provide a resource on here for alternative solutions, who are in the same situation. The trailer maker recommends spray foam in between the steel joists but I just cannot go that route (for health and environmental reasons).

    I've been reading and thinking all day and this is the best option I can think of:

    Sill seal/edpm gasket on all sides of the steel joists (to help with thermal bridging). I'm sure this won't make a significance difference but it should help a bit. I would use roxul boards (foil facing) with the foil side facing the bottom pan to act as the vapor barrier. Over the (sill sealed) joists would go advantech or plywood.

    Since you already gave your recommendation I don't expect you to dive into this further, unless you would like to.

    Of course, if anyone else wants to weigh in, I'd love to hear your thoughts.

  13. User avatar GBA Editor
    Martin Holladay | | #13

    You wrote, "I would use Roxul boards (foil facing) with the foil side facing the bottom pan to act as the vapor barrier."

    Your floor assembly doesn't need an additional vapor barrier (especially one facing the exterior.) The steel pan that comes with your trailer is already a vapor barrier.

    -- Martin Holladay

  14. Grey Wolf | | #14

    Hi Martin,

    The steel pan is not one solid piece. It is layers overlapping each-other and the corners are open. So I will have to seal all seams/corner with caulk or tape.

    I was thinking foil faced towards bottom just for extra precaution (in case the bottom wasn't 100% sealed) but after thinking more about would be far too difficult to try and seal the roxul boards to the bottom joists (for a complete vapor barrier w/ the foil).

    Can you think of any downsides (besides extra cost) if I laid a vapor barrier against the metal bottom pan, under the roxul foam board?

  15. User avatar GBA Editor
    Martin Holladay | | #15

    The steel pan is a perfectly adequate vapor barrier, even if it has holes. (The presence of holes doesn't much affect the ability of the steel pan to stop vapor diffusion.)

    If you want an air barrier rather than a vapor barrier, sealing holes matters.

    This entire discussion is confusing, however, since exterior vapor barriers generally aren't recommended (unless you are installing a low-permeance material that has significant R-value).

    For more information, see Do I Need a Vapor Retarder?

    Q. "Can you think of any downsides (besides extra cost) if I laid a vapor barrier against the metal bottom pan, under the Roxul foam board?"

    A. The danger of any exterior vapor barrier is that moisture will condense against the vapor barrier during the winter, when the vapor barrier gets cold. That worry is small in a floor assembly, because there aren't any moisture transport mechanisms that are likely to drive inward moisture downward through a floor assembly. In general, though, rigid foam is safer from a moisture perspective than a vapor-permeable and air-permeable insulation like mineral wool in this location, especially if your assembly has an exterior vapor barrier.

    -- Martin Holladay

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