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Community and Q&A

Foam-free builds

Malcolm Taylor | Posted in General Questions on

All the talk about sub-slab foam levels has me thinking. What floor systems easily allow foam free construction? Pier construction immediately comes to mind, but beyond that?

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  1. GBA Editor
    Martin Holladay | | #2

    I think that all of the possibilities have been listed.

    The least expensive (most tried-and-true) approach is a ventilated crawl space / house on piers with the insulation in the floor assembly.

    Foamglas works, but it's expensive.

    Perlite is more experimental, but people have used it.

  2. Terry Lee | | #3

    Malcolm, “all this talk about foam” this and that. You got that right! Great question this site and the industry should ask more of.

    Most that install foundation foam do not understand creep, deformation, elastic limits, safety factors, settling; live, dead, and cyclic loads, since they are not Engineers and get themselves and their buildings in trouble. Take that lack of knowledge and reduce it 2-3 times for perlite.

    Foam has a high carbon foot print, it does not degrade pollutes our landfills and oceans, it’s toxic in many applications, in it is FAR from a “green” material and I surprised this site and other ‘green’ sites recommend it highly.

    Perlite, vermiculite, hempcrete, strawcrete, clay, hydraulic limes, aerated mortars-concrete, sandwich construction, can not only be produced in many cases cheaper but, more efficiently. A composite sandwich construction using these materials as insulated core, with stronger cement skins, is very effective. There are MANY material choices you can find locally, you meet code using the analytic path and mounds of test data on the internet and a PE which is whom one should hire for foam applications anyway. I have an open dialog with my B&S office now, they are receptive.

    Due to the high silica content of many of the materials I listed above, they do great around wood frame work too, many are CO2 and CO negative, no VOC.

    Due to the nature of the materials properties can vary. I am in the middle of structural test on some now, getting ready to test u-values. You will not see one once of foam in my building's.

  3. Aj Builder, Upstate NY Zone 6a | | #4

    Perlite has my interest but I'm not at all afraid of rigid foam under a slab or in basement walls. I think rigid foam and OSB in any build is nuts. OSB is junk. I do use it, try not to. SIPs glue foam tight to crappy OSB which is good in that there is no moisture holding gap. When a carpenter nails foam to OSB, there is a gap for water, for rot.

    Anyway Terry Lee, you are entertaining my man. Foam is bad? Rediculous. What man made wonder of the last century do you approve of then? Don't bother explaining, I got it.

    The one place to use foam if any place, is in foundations. Says aj builder. Quote me anytime and anyplace.

    Semi green builder mostly blue. (think blue sky's blue waters... get off the planet yo... go sailing in the sky or on the waters or dive in to it as I did this week for work. Nothing more fun than using air tools at the bottom of the lake building docks! (we oil with vegetable oil))

  4. Jerry Liebler | | #5

    In addition to perlite there are other insulating "rocks" such as Scoria and Pumice. Perlite is essentially universally available at low cost while the others may have to be "imported" and cost more. Perlite being somewhat man made has more "controlled" characteristics and a higher r value/ inch. With appropriate compaction any of these will have compressive strength greater than any foam and most soils. These rock materials do not suffer from creep under long term stress (plastic foam does) and they are immune to attack by termites and other "critters". A potential downside of all the "rock" insulation is they loose their insulating property when saturated with water so they must be kept well drained.. Unfortunately use of these materials is considered "experimental" while compacted fill of local soils is routinely used under slabs and footings.

  5. Peter L | | #6


    You stated:
    "Foam has a high carbon foot print, it does not degrade pollutes our landfills and oceans, it’s toxic in many applications, in it is FAR from a “green” material and I surprised this site and other ‘green’ sites recommend it highly."

    If you are that against EPS that you believe it does not belong in "green" buildings, you are the .01% of the environmentalists and you might as well turn off your computer and unplug from the grid if you are truly that die hard. You are destroying the planet by logging on and blogging on this and other sites. The electricity you are using is coming from a coal or nuclear power plant.

  6. Terry Lee | | #7

    Jerry, right! Here is one data sheet they recommend doing a deflection analysis on your slab installation loading to yield @ 10% deflection they give you "recommend" live/dead loading to avoid max creep over 20 years. Some will use a safety factor of 3-5 to prolong the creep. How may do you think do deflection analysis and load at Ultimate? Most are at least at yield unless they went with the higher allowables. Most are probably crushing it especially at center, increasing it's density not getting the rated r-value. Can you imagine the ones wrapping it around the top of piers on footings without doing the proper deflection and moment checks.

    I heard of pumice not scoria, I need to look into them. The difference between perlite and vermiculite is perlite drains better. I'm working on a test block attached for a interior pony wall that had ugly paneling on it. The footing is exposed to the exterior, this is a garage remodel I am renovating. Instead of foam I will design an insulative cast in place mortar, non structural, using vermiculite to the interior surface since it has humidity control and iron oxides I will be adding more of for aesthetics. The silicon in it should bond well with the binders I am using. I'll run a simple test to see if I am bridging to determine how much verm I need.

    Heres a good read Martin did:

    I would not use it alone in bags, I go to a binder but not portland cement unless I had to.

  7. Terry Lee | | #8

    I don't know why my pics attach fine but won't show in my post?

  8. John Brooks | | #9

    edit to say ...hmm I tried to post a photo
    it is not working for me either

  9. Nate G | | #10

    Scoria is cool stuff. It's used everywhere here in New Mexico for landscaping, but it's very lightweight and has insulating properties as well. Natural builders estimate that it's about R-2/inch. Area hippies fill earthbags with it and claim the walls offer about R-30. It would be great to get an official study done on the properties of scoria one of these days. Seems like a great untapped resource in places where it's plentiful.

  10. John Brooks | | #11

    Martin, FYI the "test" photo that you posted is not visible to me...
    I am using Internet Explorer

  11. GBA Editor
    Martin Holladay | | #12

    I can't see the photo either. Our tech team is working right now to see if they can fix this new bug.

    We are grateful to GBA readers who brought this to our attention. Thanks.

  12. Aj Builder, Upstate NY Zone 6a | | #13

    Terry your whole approach is interesting but also foam does do a job today at least in foundations for me today. GBA should have a tab dedicated to you. It's all interesting but if I were to want to use your ideas I would have to have a PHD is research methods to find and combine all your comments and then try to implement.

    You need to start a blog and point us all to it. And start to publish and share your methods to date, pictures methods results.

    All this talk with out the back up of reviewed projects is useless to us and to the community in total.

    Time to publish completed and reviewed projects Terry. Many of us would be interested. The many tidbits in posts denigrating all other ideas not so much. Many of us would prefer to never or rarely use foam, etc, so we need alternatives like your not so well published methods entail.

  13. Terry Lee | | #14

    Foamglas looks like a great product. I find the sub structure requirement interesting "light concrete mix" , level compound, and 'hardcore" pack soil. They do all they can to minimize deflection and creep which are two different stresses based on elasticity (MOE), but since their panels do not distribute load evenly over the entire foot print it is limited. That is why they call for the sub structure tight flatness requirements, to try and minimize deflection-creep deltas resulting in surface tension cracks in the foam and slab. Notice too they want to review your plans and specifications stating the webpage info is only a basic guide. They do offer a high compression strength, but that is only one stress of concern, hence the plan review.

    If you replace their foam with a "light concrete " mix with perlite and TY 1A portland cement for example, over the entire slab, you improve distributed compression loads and reduce them to a larger area , also improve r-value and drainage. The actual amount would depend on thickness determined by an structures engineer. Perlite is easily proven and designed by an engineer nothing new, nor are the many lite concrete mixes on the market available for structures analysis by a licensed PE, not builders, for centuries now. If you want to optimize cost, you do the research, look at your local market and resources as I have for material substitutions. Some may find materials are lower cost than others depending on locality. AJ: I got nothing to share other than what fits in my zip code I am searching for and testing for now, otherwise the process is the same, due your local home work and do not look for a hand out. I can assure I have not invented or discovered no new material or process that has not been around since day 1 of earth existence I will obtain a global patent for, I wish, so don't hold your breath ;)

    This is an interesting read, but it fails to look at 'combined loads'. You can not just compare foam compression to soil, nor how compression is distributed. Soils have different properties than foam. In structures analysis there are many load cases that are checked, compression is just one. Cracks occur in tension, not compression.

  14. Jason Hyde, Peterborough 6A | | #15


    Thought you might find this interesting, was new to me.

    I've tried to get some discussion going, but no response thus far. Roxul comfortboard CIS's compressive strength is listed as 1220 PSF (10% deformation). According to the comments, the Roxul engineers are 'ok' with it, whatever that might imply - if anything.

    Side note, anyone know what that "cement board" is they used to clad the slab edge with?


  15. Expert Member
    Malcolm Taylor | | #16

    Thanks Jason. Interesting stuff. I'd imagine Roxul and perhaps others will come up with a few variants on their rigid products to take advantage of the foam alternative market.
    I'd imagine the cement board was something along the lines of hardi-backer.

  16. GBA Editor
    Martin Holladay | | #17

    Thanks for the link.

  17. Richard Beyer | | #18

    AJ said; Terry... "GBA should have a tab dedicated to you. It's all interesting but if I were to want to use your ideas I would have to have a PHD is research methods to find and combine all your comments and then try to implement."

    Aside from your constant insults on people you disagree with, my interpretation of what Terry is saying is this.... Modern homes and materials are best left up to an engineer to dissect. "Builder's" should build and leave the technical aspects to a professional who understands. Too many builders today pretend to understand. I think Terry is right on! Why would any sane builder want to be bogged down with all these technical details. It's not going to make you any more money as it will prove to cost you plenty of it in research time and misunderstandings. Just my opinion.

  18. Aj Builder, Upstate NY Zone 6a | | #19

    Richard none of my last post was an insult. Rediculous! Look, when a builder builds we are not handed a list of materials to build with. You must know that. We don't have a budget to hire an engineering team to write up the material list. How possibly can you not understand that???

    I like you and Terry and women and Martin and all of you. Stop taking offense at every post I make. Rediculous really. Meet me in person and we may just be able to enjoy a chat about the benefits of using Schluter products. How the heck would I know to use them if I didn't enjoy sites on the internet and asking millions of questions of my inspectors , other pros, engineers, archs, going in builds that are in progress.

    Builders do not get a list of materials handed to them from any one. They have to choose the materials themselves.

    Tell me I'm wrong about this and I will go some other way.. silly.

    not insulting...

    I have built hundreds of builds, none of the plans, none came with a complete material list. None. Some came with some materials as I have built some kit homes.

    Plans come with basic specs. You must know that. Do you have any plan sets? If not, I have dozens, stop by and we can open up a few sets.

    aj said ".... get a life" I am not trying to insult... I am making my point absolutely clear that Terry and I differ as to the need for teams of engineers. such as spec'ing foam for under a slab. Foam is being placed under thousands of slabs for decades now. It is common practice to do so without an engineer involved I am the following the norm Richard. Ask Martin, Call Dow. It is a norm today. Call the engineers at Dow. They will confirm that it is the norm Richard.

    Engineers design and manufacture the foam. Builders use the dang stuff where manufacturers say to use it. Somehow we find out about a product. One place is GBA. Another way we learn is to use a product like OSB and decide it is low quality just as we learned to plywood made with less plys is not so good, just as we found early run imported plumbing valves were not made well, just as we found when electric wire started being made overseas it was brittle, be careful twisting on a wire nut as a wire may break inside the twist and you may not know it. Been there Richard, still there Richard.

  19. Jason Hyde, Peterborough 6A | | #20

    Got a response on (thanks Andre!).

    See the response to my comment made on Dec 12. Andre provided a link to an article, by Alex Wilson, on As I am not a paid member, I could not read it, but the (article's) comments have a few interesting links.


  20. Expert Member
    Malcolm Taylor | | #21

    Jason. Thanks again. For me anyway, this changes everything.

  21. Lucas Durand - 7A | | #22

    Interesting stuff, thanks.

    Kinda complicated slab detail for the bird house I thought.

  22. Jason Hyde, Peterborough 6A | | #23


    I tend to agree. My guess is the foam glass block on top of the footing is to elevate the slab (and stud wall) relative to the grade. Even though the detail shows a framed wall, I would say 75%~ of the basement is actually CMU.

    Also curious what the drainage membrane is they used for the skirt insulation. I didn't see any mention, or photos in the blog. EDPM pond liner maybe?


  23. Jason Hyde, Peterborough 6A | | #24


    Glad to help. I noticed they actually used the Rockboard 80 for the Maryland PH, which is a considerably lower density than the CIS line. The blog mentioned they plan to switch to CIS in the next build.

    I would be interested to know what kind of deformation (%) can be expected when the CIS product is used under a typical slab. The tech sheet only lists 1220 PSF @ 10%, which in my opinion, would be intolerable for a slab. Even with 4" of insulation, that's almost 0.5" settlement, with 8" it would be a 0.75"~.

    Now if only foam glass was a little easier to find in these parts.


  24. Jin Kazama | | #25

    Malcolm you want to use green only materials, well pier is probably the only way.

    How much carbon is in the concrete slab on top of that EPS ??

    Just for kicks

    20X30 house
    6" concrete slab = ~ 20k kg = ~ 3180kg of co2 and ~ 6100KWh
    6" EPS @ 20kg/m3 = ~ 425kg co2 and ~ 4500 kwh

    same insulation in cellulose = 0co2 ( 0 really? ) and ~ 1000KWh ( adjusted for same R value )

    Concrete energy savings during lifetime = 0
    insulation energy savings decide

    If you wish to have as less impact as possible,
    build on piers, wood trusses and fill up with cellulose ,
    only use foams as minimum as possible or find suitable alternative with less impact.

    but hey ...i might be completely off here..just playing with numbers :)

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