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Community and Q&A

EPS Foam for Subflooring

thegiz | Posted in General Questions on

So dricore has a product called insularmor that states you can apply finished flooring right over it. It’s a high density eps, there is nothing special on it that makes it a fire barrier layer which I understand is why you need plywood over eps. So if you are allowed to put finished flooring over this why can’t I simply find a 1/2 in high density eps to use under lvp? I don’t see the difference and hd eps I understand can support up to 4000 pounds. What the heck is going to be that heavy to cause potato chip curling on your eps. Also if I even worried about potato chip curling couldn’t you stagger 2 layers of hd eps? If fire barrier is the only concern is there something thin you could use to cover the eps. Also none of the lvp brands have a fire barrier built into floor? I would also think a thicker lvp combined with hd eps would be an extra precaution because your lvp is more rigid.

just me rambling as usual – Hammer

DRICORE ® Insul-Armor™

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  1. Expert Member
    NICK KEENAN | | #1

    It's a building code thing. The code says foam insulation has to be covered by 1/2" of drywall, 3/4" of plywood, or "other approved covering." For example, you can buy polyiso foam that has a coating that has been tested and approved to act as a fire retardant barrier. Any such material has to be labeled with the code reference and testing agency.

    I couldn't find anything on the Dricore website as to whether they meet code requirements. The only reference I could find is in the warranty, where they say failure to meet code requirements is not covered by the warranty.

  2. Expert Member
    Michael Maines | | #2

    That product is rated for 3650 psf, which is 25 psi, the same as any Type 9 EPS. Typical marketing hype to focus on the square foot rating when it's point loads that will cause damage. The rating is for 10% deformation which means that for 1" material a load of 25 lbs spread over an inch will compress about 1/8".

    Did you read the installation instructions? They rely on the LVP to spread out the loads; with carpeting they require a plywood-type covering. If you want a warranty, I would check with the LVP manufacturer to make sure they are ok with installation over foam.

    I don't know why they are allowed to sell it if it doesn't have a fire retardant. The fact that they don't list any supporting documents is suspect. I take fire risk seriously and would want to keep my family safe in case of a fire. I just emailed them to ask about fire ratings.

    The code provisions for foam plastic are in R316:

  3. thegiz | | #3

    Here another product with same installation, lvp can go directly on top. Don’t see anything about fire retardant either. It has a much lower r value but I’m confused as why this is also allowed

    Dmx one step has a built in thermal barrier but from my understanding on reading forums air gap technology is considered overrated and the r value in this stuff is too low to prevent condensation under the lvp

    1. Expert Member
      Michael Maines | | #4

      There are special provisions for foam plastic--what we call foam. Other materials have different requirements, which vary slightly whether they are finishing materials or insulation. R302.9 and 10 here:

      Air gaps do provide insulating value, and it doesn't take much to raise the floor surface above the dewpoint temperature. I think on previous threads I had said that R-3 to R-5 should be plenty, and others in warmer climates said even less could work. The R-0.5 cork/plastic (EcoCorkFoam) won't do much insulating but it might be enough to prevent condensation.

      1. thegiz | | #5

        I agree with what you stated somewhere earlier that as a designer for other people’s homes you can’t have any risky application even if the application was low risk. These are the thoughts going through my head with different method again I’m not a building scientist by trade.

        1. The ecocork foam has an attached 6 mil vapor barrier on top of foam. The insulation is not nearly enough to prevent condensation but the 6 mil vapor barrier would reduce air flow to slab and any condensation that occurred on slab would have to evaporate up and would eventually hit underneath the 6 mil plastic. If we are worried about air bubbles in 6 mil vapor barrier causing mold when directly attached to concrete this would create space. If this material can live with constant moisture is another question.

        2. Dmx one step also does not have enough insulation to prevent condensation. In theory the air gap would allow water that condenses on slab to evaporate. Maybe this is just an extra insurance if we don’t want moisture trapped under vinyl.

        3. If lvp is truly an air barrier then condensation can’t reach the slab because air is blocked. If this is true direct lvp on concrete is actually safer.

        1. Expert Member
          Michael Maines | | #7

          Hammer, I could be wrong but it sounds like you are still not quite understanding the two issues at play. Until you understand the two issues it's going to be hard for you to make a decision.

          1. Condensation forms when air hits a cold surface. In your case, with LVP, most or all of the condensation would form on top of the LVP because it's not a vapor-permeable material. A tiny amount might occur below the LVP, on top of the vapor retarder. Virtually none is going to get through both the LVP and another vapor retarder to condense on the slab itself. If you use carpet, which is vapor-permeable, condensation would occur wherever the first impermeable surface is below the carpeting.

          2. The other thing that is likely to happen is moisture from the ground coming up from below, in the form of liquid water or water vapor. That could be trapped by poly. Maybe you are calling this condensation but that's not the right term; it's groundwater. It won't condense because it's not water carried on air and it is going from cool to warm, not warm to cool. Whether the risk is high enough to worry about was the subject of debate but people who know more about mold than I do thought it was risky.

          Back to condensation, which only occurs when relatively warm, moist air hits a surface cool enough that it can't hold its moisture. The slab surface will likely be around 50°F, possibly high enough to prevent condensation without insulation but a little warmer would be safer. So R-0.5 just might be enough; it's hard to say. More insulation would be safer.

  4. Expert Member
    Akos | | #6

    I've worked with high density EPS and it can still be dented.

    The weak point on any click LVT is the click area, very essay to break these if not properly supported. Heel strike usually puts about 1.5x the person's weight over an area of a couple of square inches. 25PSI foam is no match for that much concentrated force, it will dent and eventually bust the click in the LVT.

    You need solid plywood/OSB for these, no way around it.

    1. Sofiane | | #61

      Would a cork subfloor work as well?

  5. thegiz | | #8

    Thanks for the input. In terms of application I’m going to need either a thicker floor with insulation and plywood/osb so that it can be rigid enough to walk on. Or I’m going to need a thin enough floor that weight will be deflected to concrete. Is .5 R enough, maybe but could be risky as Michael said. In terms of R value I wonder if using a 1/4 inch polyiso would be an option. That’s r 2 correct, and doesn’t lvp like lifeproof have an attached pad. Doesn’t the flooring itself have an r value? Then again if deflection is 1/8, 1/4 foam might still not be rigid enough.

    Best option with low risk and lowest height would prob be 1/2 eps and 1/2 inch plywood. Inspector might come one day and ding me for being under 6’4’ under ductwork but I would tell him it was choice of slightly under or possible mold growth.

    1. Expert Member
      Michael Maines | | #10

      Hammer, deflection for foam is measured at 10% of the thickness. So for 1" foam, at the maximum rated load it will deflect 1/10". At 2", it will deflect 2/10". If you are using 1/4" foam it will only deflect 10% of that--0.025", or about 1/32".

      Softwood is about R-1.2 per inch of thickness. Hardwood is about R-0.7 per inch of thickness.

      I have no experience with LVP but it likely has very little insulating value. Dead air is what provides insulating value--the tiny cells in wood or foam. There are basically no pores in dense vinyl such as LVP.

  6. Expert Member
    NICK KEENAN | | #9

    Can you move the ductwork?

  7. thegiz | | #11

    The ductwork is my main trunk runs along side the main beam. The clearance is 6’4’ under ductwork and is 6’5 under my lowest spot of main beam. The ductwork could be replaced with a wider and shorter trunk, don’t know how expensive that would be. I don’t know what inspector would do if clearance is under 6’4’ not sure if there are consequences, I’m assuming could also be how strict inspector would be. If they just don’t allow you to use as finished square feet I wouldn’t care because I’m not selling this home or renting it out. So I would like a finished floor with a maximum height of 1in. In that scenario I will never get a 0 risk floor outside of tile which I don’t want. Just trying to think of a scenario where my risk will be lower than doing nothing under finished floor. My choice of finished floor thickness and material would also be a factor. Painting concrete and using area rugs is an option but probably something I would have to consistently monitor.

    1. Expert Member
      Michael Maines | | #12

      The codes for clearance are mainly so when you or an emergency responder are trying to get you out due to fire, you/they don't bang your head and get knocked out. I would not recommend this for a client but if you're going to cheat a bit, you might consider wrapping the corners of the duct with something soft.

      Now that I know more about your situation, I think I would consider this assembly: coat the concrete with something to reduce water transmission, lay down 1/2" EPS (type 2, 15 psi), cover that with 5/8" OSB fastened to the concrete through the foam with tapcon screws, paint the OSB with epoxy paint. Use thin area rugs as necessary. The difference in stiffness between 1/2" and 5/8" OSB is significant.

  8. thegiz | | #13

    Thanks Michael, sounds like a good option to consider. I could possibly also peel and stick on a top veneer layer over osb or just paint as suggested. I’m just surprised that they don’t have an engineered hardwood or laminate that would be rigid on it’s own. I’m assuming lvp would be weaker than both because it has no wood particles in it. I guess the problem is more of the locking mechanism between the boards. I understand that some engineered flooring is a plywood backing with a veneer hardwood. However plywood or osb boards must just have more strength. Even more strength than a thinner hardwood.

    1. Expert Member
      Michael Maines | | #14

      My office floor I'm on now is A/C fir plywood with polyurethane on top. I cut the sheets into 16" strips and rounded the edges before installing with screws. It's not fancy and won't last forever but it was cheap and easy, important considerations at the time, and several people have mistaken it for wide-plank flooring. I've also lived with painted plywood or particleboard floors in previous homes. Any separate finished floor is going to add some height so I just thought painting your subfloor would save you that 1/4" or more. I really don't have much experience with the various plastic floor products.

  9. thegiz | | #15

    New dmx product claims it is specifically made for this purpose. With a 50 year warranty not sure exactly what they are covering thougH

    1. Expert Member
      Michael Maines | | #16

      Haha, you've posted that before, and my proposed assembly above is nearly identical to what I recommended when you started asking about this many weeks ago. We've come full circle. It's time for you to make a decision and move on.

      My two cents on that product: it's too thin to have a useful amount of foam for insulation. The air gap will provide a bit of insulation. There is a good chance it will be enough to prevent condensation. There is also a chance that it won't be enough.

  10. thegiz | | #17

    Thanks for input, yes that product is slightly different but essentially the same thing. I think your idea is the best option considering the height restraints. It will also be safest against any mold, safer than laying vinyl directly on slab which may be fine but don't want to take risk. My only concern would be splintering of wood or the finish of wood on top for my toddlers at home in areas where I didn't have area rug. I'm thinking a higher grade plywood might be smoother without increasing cost too much. Would hardboard or another wood product be an option? I know Walter mentioned the possibility of using a 1/4 hardboard in another forum but said it would be risky. Not sure if 2 layers of 1/4 inch hardwood is stronger than a 1/2 inch plywood.

    I can't help but wonder why there is no laminate or engineered hardwood that is rigid enough to sit on foam? Some of the products come with plywood backing. So you basically already have plywood built into product. Fire resistance would be covered because you are not putting plastic over the foam. If the compressive foam underneath was high enough and the finished floor was rigid enough I would think it wouldn't deflect enough to the point were the locking mechanism would unlock. Just a thought since the surface would be finished and if the product is made rigid enough it could sit on high compressive foam. I would also think a 1/4 plywood/hardwood might be able to support a thick laminate if the laminate had built in rigid backing. For example the box stores have 12mm waterproof laminate that's nearly half an inch on it's own

    1. Expert Member
      NICK KEENAN | | #18

      Plywood prices are so high right now that the local Lowes has maple and oak plywood for the same price as sheathing.

      1. Expert Member
        MALCOLM TAYLOR | | #22


        When that happened a couple of summers ago I designed a she-shed for my wife using 3/4" birch plywood as studs and sheathing. It was almost the same price as 5/8" exterior grade plywood and had the advantage of being a nice interior finished surface too. It all got protected by exterior foam.

        1. maine_tyler | | #29

          That's a neat build Malcolm.

    2. charlie_sullivan | | #19

      Two layers of 1/4" ply would give the advantage that you could stagger them so there's no seam that isn't bridged by 1/4" ply. Ideally, glue those layers together with simple wood glue. With high density EPS and hardwood ply, that would work well, although I'd feel a little better about 3/8" ply.

      The reason flooring panels aren't rigid enough is because they don't have a way to bridge the seams, like you can with overlapped layers of plywood.

  11. thegiz | | #20

    I keep hearing about plywood prices, I'm not in the business so I can't remember the prices I think they are double what they were before. Where I am in NY 1/4 4x8 sande plywood is 26.92 each, 1/4 4x8 birch 29.93. I'm assuming I would need birch if it's more money must be more durable. For a 300-400sq foot of flooring I might have to wait until plywood prices drop. I don't know how much more it will cost me to do now compared to if price actually goes back to normal.

    1. Expert Member
      MALCOLM TAYLOR | | #21


      Each type of plywood has it's own uses. Birch plywood is typically cabinet grade with smooth finish. That's why it costs more, but it isn't what you want as an underlayment.

      None of us know when or if prices will drop.

  12. thegiz | | #23

    What would be best plywood to use here with a double layered 1/4. If smooth surfaces are more expensive I could only use nicer surface for top layer only.

    Saw a guy on YouTube layer cork flooring right over hd eps. Not sure what happened there

  13. thegiz | | #24

    Plywood is so damn expensive right now. Is there a way to use tile backboard? Better yet create a subfloor using the insulated backer board with some combination of wood. I don't know the compressive forces of traditional backer board or the insulated type but with plywood prices so high it's no longer a clear cut answer to use plywood. I could understand before when it was cheap but now there's not such a great difference in price with other materials

    1. Expert Member
      MALCOLM TAYLOR | | #25


      Right, but are these "other materials" appropriate to use? Mostly why you see plywood used on walls, roofs and floors is because it was specifically developed for that purpose. A good rule or thumb is the if you haven't seen something used in a certain situation, or something done a certain way, there is very likely a good reason why.

  14. thegiz | | #26

    Malcolm this is true but came up with an interesting question that might actually apply here and be debatable. So I stumbled upon wood fiber board by Steico. It’s available on Amazon, checked back here for info on it and read Michael Maines article

    So seems to be mold proof, is eco and green. Apparently it can be used in sub slab insulation and is much more rigid than eps. I also might add that it’s only recommended for above slab insulation. Don’t have numbers here but Steico claims rigid enough to use under lvp laminate etc. Claims for mold proof is that it is vapor open and allows moisture to escape. The whole argument we had on another forum is if drying to the interior in a basement was necessary. So could this product be used as an underlayment? Would my top layer need to be vapor open as well?

    Seems like a viable option based on what I read in this article. As always I’m a novice so I’m probably missing something here, just hope I’m not.

    It’s on Amazon as Steico 1/4 in flooring underlayment

    1. charlie_sullivan | | #27

      I think you do not want vapor open. You do not want water from the conditioned space condensing on the cold slab.

  15. thegiz | | #28

    Isn’t it made differently, it’s not like cellulose which is newspaper and closer to mdf or Masonite. I’m taking this from article explaining a difference:

    Wood-fiber insulation and cellulose insulation are made from the same raw material, but cellulose is newspaper, whereas wood fiber comes from softwood chips. According to GO Lab president Josh Henry and marketing director Matthew McConnell, the company is gearing up to produce wood-fiber insulation in a former paper mill in Madison, Maine. They describe the process of making it as similar to making paper. There are two ways to do it—the dry method and the wet method—and each results in a product with different properties. Similar processes are used to make medium-density fiberboard (MDF) and hardboard such as Masonite.

    One of the most exciting things about wood-fiber insulation is the size of its carbon footprint—it’s miniscule. In Europe, it’s carbon negative.
    The wet method has been around longer and is more like paper-making: Wood chips and shavings are ground and mixed with water and binding additives, and the pulp is then compressed and dried. (The reclaimed water is used in the next batch and scraps are mixed back in with fresh pulp.) The result is relatively dense sheets up to 3⁄4 in. thick, though they can be laminated with water-based glues to make thicker boards.

    For the dry method, the ground wood fiber is dried, then mixed with a pMDI (polyurethane) binder and paraffin wax for water resistance, compressed, and cured with steam and pressure. The result is a wide range of available densities. This method uses up to 40% less energy than products made using the wet method.

    The composition varies a bit between manufacturers, but even more so by product type: board, batt, or blown. Common dry-method boards such as Gutex Multitherm are 95% wood fiber by weight, 4% resin binder, and 1% paraffin wax. GO Lab is planning to make a batt, similar to those on the European market, containing approximately 85% wood fiber, a polyester binder, and ammonium polyphosphate (a common food preservative) as a flame retardant. The blown-in is usually composed of wood fiber and a flame retardant such as borate.

    1. maine_tyler | | #30


      Which Steico product are you looking at specifically? I'm interested to see their write-up on it.

      Note that you wrote: "Apparently it can be used in sub slab insulation and is much more rigid than eps. I also might add that it’s only recommended for above slab insulation."

      Obviously that's contradictory, so probably a typo. I did not think wood-fiber insulation was suitable for below grade. I didn't even think it would be good for contact with a basement concrete floor, but I'm not positive on that.

      I would tend to agree with Charlie that you don't want interior moisture to pass through your flooring, allowing condensation on the concrete. That would be the dominant vapor drive direction, as discussed in the previous lengthy thread.

      One thing that might quell some of your nervousness about this (which has probably been mentioned before) is to plan on keeping RH in check (i.e. run a dehumidifier). If you do that, it's much easier to be sure a thinner insulation layer will be 'sufficient for dew-point control.'

    2. Expert Member
      Michael Maines | | #31

      Hammer, I believe Charlie has a typo and meant, "you do not want water from the conditioned space condensing on the cold slab."

      I love wood fiber insulation, as you might be able to tell in my article you quoted from above. But I would not use it where it would potentially see water or moisture accumulation, as it has little resistance to fungal attack. I avoid foam whenever possible but there are some situations where it's a natural fit, such as above or below basement slabs.

      The Steico underlayment you linked to is rated for 21 psi (~3000 psf) so a little better than type 2 EPS and not as strong as type 9 EPS. At 1/4" thick it will perform at about R-1, if it stays dry. That might be enough to prevent condensation on the floor surface. If the floor surface is impervious then air won't be able to get through the insulation to condense on the slab (or poly, or fluid-applied coating). I would not trust any flooring to be impervious but it's your house so you could experiment.

      1. charlie_sullivan | | #35

        Thanks, Michael, for correcting my typo. Your interpretation is correct.

  16. thegiz | | #32

    Thanks Michael it was a great article. Maybe I could combine it with eps and layer it. 1/2 inch eps and 1/4 wood fiber board. The wood fiber is cheaper than plywood right now, compressive force maybe still a problem but stronger than eps and I believe would cover fire resistance. I think with 1/2 inch eps and the wood fiber board I’m up to r4. If the finished floor is impervious the wood fiber should stay dry correct?

    Tyler you are correct that a dehumidifier would help control rh and make thinner insulation a safer bet. Similar concept to putting down carpeting and running a dehumidifier as some have mentioned that they do to control mold and mildew in carpet

    1. Expert Member
      Michael Maines | | #33

      Most wood fiber insulation has no fire-resistant qualities. In fact it's loaded with paraffin. Loose-blown and batts have borate fire retardants added but the rigid stock does not, as a rule, though there may be some exceptions. 1/2" EPS is R-2 and 1/4" wood fiber is R-1, so you'd be at R-3 total. The same as using 3/4" EPS. You would be better off using 3/4" Type 9 EPS which has better compressive resistance than wood fiber. I'll quote my own post above: "I would not trust any flooring to be impervious."

      You win the award for highest level of analysis paralysis I've ever seen, which is saying a lot.

  17. thegiz | | #34

    Ok yes I over analyzed, type 9 eps with a 1/4 hardboard should be enough strength. I will coat concrete with liquid membrane, throw down the eps and wood paint it and throw down area rugs. Where do they sell 1/2 type 9 eps?? Do they even make it thinner?

    1. charlie_sullivan | | #36

      EPS is often custom formed by local businesses. You can find a map of them here:

      A few in your region are and

    2. Expert Member
      Michael Maines | | #37

      I don't mean to sound harsh, it just really is remarkable how thoroughly you've considered this situation!

      I order EPS here: They can make it pretty much any size and thickness you want. There is a cost for shipping but it's pretty reasonable.

      When you say hardboard, do you mean a product like Masonite? I don't think a single layer of that will work very well as flooring but you could give it a try. Before Ramboard became the default for construction floor protection we used to cover floors with rosin paper and Masonite. The field of the panels held up well but the edges always frayed. Sometimes we'd use 1/4" Luaan plywood but it's very soft and splintery. If you can keep the edges protected, maybe Masonite would work. It's very smooth and hard so you'd want to sand it before painting.

      At some point there was talk about two overlapping layers of plywood, which I think could work--I'd use a marine-grade plywood which has no voids and high-quality veneer that doesn't splinter readily. But it's not cheap.

      I think the best balance for your constraints would be a single layer of 5/8" A/C fir or SYP plywood, screwed through the foam into the concrete. A/C plywood is a little splintery but if you sand it and round the edges over before installation, and paint it, it should be ok. My office floor, as I think I mentioned, is A/C plywood with a polyurethane finish. After several years of use there are some dents and the finish was flaking off under my chair, so I added an office floor mat.

  18. thegiz | | #38

    Thanks for the help. If I still need the same amount of plywood then there is no need to special order high compressive foam. I was only going to do that so I can use thinner plywood or a thick laminate directly over it. However if that will never work it is not worth it. The type 9 foam is not so easily available is a 1/2 inch thickness. I checked out the links to foam manufacturers I will try contacting them but I’m assuming cost will be higher than something I can buy in a big box store. I’m going to use the ac grade plywood but I’m going to take the risk with a 1/2in not as rigid as 5/8 but I think it can work.

    Layering 2 1/4 plywood and floating it would of course be preferred rather than having to directly screw into slab. What eps would be something I could use here that they sell at big box stores that can be readily available? I’m thinking buy the eps cheap and maybe source my plywood from the local lumber yard. I will pay higher for lumber but I will probably get a nicer piece of wood and they will have ac grade in a quarter if I want to layer it.

    1. Expert Member
      Michael Maines | | #39

      I'm not sure what density EPS is available at box stores but it's likely type 1, only 10 psi and too soft to use for much of anything. Before making a decision (what's the rush at this point?!) I'd encourage you to contact Branch River Plastics and/or your local manufacturer and see what the cost would be to have it delivered. I've found that in most cases, type 2 EPS is about the same price, custom-cut and delivered, as buying XPS at the local lumberyard.

      5/8" material of any type is about twice as stiff as the same material in 1/2" thickness. I would skimp on foam thickness before skimping on plywood thickness.

      One problem with floating two layers of 1/4" material is fastening them together, 1/4" is too thin for bugle-head screws to set flush without first drilling counterbores so the heads can sit flush.

      Before committing to a system, I recommend buying a small quantity and doing a test run.

  19. ar_t | | #40

    Dear Hammer,
    Why not start from scratch and knock out the old floor, make it deeper for clearance, put in a raft slab or similar, which Michael Maines, and Steve Bazcek, among others have described and written about over months, if not years. You’ll have your fire resistance, a warm floor and more headroom.
    Do it once, right, forever and forget it.

    1. Expert Member
      MALCOLM TAYLOR | | #41

      This thread reminds me a bit of the guy in front of you at Burger King taking half an hour to decide on the toppings for his Whopper - and still just ending up with a fairly un-satisfying lunch.

      1. Expert Member
        Michael Maines | | #44

        Malcolm, true, but we've also explored all of the options for every ingredient and cooking style, and hopefully learned something in the process. Although now we're apparently revisiting why plain white bread isn't the same as brioche buns.

  20. thegiz | | #42

    Ripping out the entire floor would be great but I have an inch to work with, not much but it would be easier than starting from scratch. I don’t understand the reference to Burger King but I wouldn’t be so neurotic if it wasn’t for my kids hanging down there. Just want a risk free floor working with the space and budget I have. If I was a builder I would probably have more options and know how. 5/8 is worth it if it will make a huge difference but why does it need to be attached to the slab? If I’m not building walls on it and it is just for carpet. Just to compare the r+ dricore panels have osb with foam are 1 inch and they float. I would like to replicate the same make up since it will be sealed better and about half the price. Why can those float because of a locking mechanism?

    I will call the eps foam manufacturer. To see what they can deliver and if they actually recommend what grade eps.

    1. Expert Member
      Michael Maines | | #43

      You want to just float the plywood over the foam with no fasteners? Have you ever worked with plywood or OSB? Without a mechanism to lock each sheet together, the edges will curl and move against each other, causing squeaks, splinters and possibly pinched fingers.

      Let me know if they recommend a compressive resistance different than what I recommended.

  21. thegiz | | #45

    I called they explained it to me as pounds. The have 1, 1.5, and 2. He said go with 2 with a 1/2inch foam and 1/2 plywood or osb. It was reasonably priced but problem was the shipping he said would cost more than the foam. He’s calling me back with a price for shipping but I might have to source it closer to home.

    1. Expert Member
      Michael Maines | | #46

      Interesting, engineers always seem to specify foam by the compressive strength, and documents usually refer to the ASTM type, but it can also be classified by density. 2-lb is 25 psi, type 9. I think it's overkill but better safe than sorry.

  22. thegiz | | #47

    So getting type 9 eps seems to be an issue. All the eps manufacturers above stated I had to be a distributer to sell me anything. The only place willing to sell to me was branch river but told me the shipping would involve 1 truck traveling 2.5 hours to me. I'm thinking probably expensive waiting to hear from them on price. My local lumber yard has no idea what they are selling and only explained to me as blue board. I think foamular in home depot is 15 psi but it is XPS. I know that it is bad for environment but it's already made and sitting on a shelf. The damage has been done already if I buy it. The other option is to buy dricore R+ panels which is 2x2 and 1 inch high with an r value of 3. However it's 7 and change for one 2x2 panel. Plus seams galore I would think and I can't tape the eps like I could be laying myself.

    1. Expert Member
      Michael Maines | | #48

      Last month I got a quote for 106 sheets of 2" EPS from Branch River, delivered 4 hours away for a $425 delivery fee, or $3.86/sheet (plus the cost of the material). Two years ago they delivered 8 sheets of 2" the same distance for $110, or $13.75/sheet. If you only need a few sheets it may not be worth the expense; I'm not sure how big an area you're planning to cover.

      When buying new XPS the damage may have already been done, but they will replace what you buy with new material so it's really not a valid argument. That argument does sort of work for buying recycled material. But with 1/2" material it's not a lot of volume so if there is a big price difference I wouldn't worry too much about using new XPS in the quantity you'll probably need. The environmental impact will be something like burning 2 gallons of gas for each sheet. You can tape high density EPS, it's very similar to XPS, just slightly more crumbly at the edges. The XPS at Home Depot is likely 15 psi, just like type 2 (or type 11), 1.5-lb EPS.

    2. charlie_sullivan | | #49

      If you want to go through home depot, call up the pro desk at your local store and ask about special ordering Owens Corning "NGX". Supposedly they are able to order it, and that reduces the climate impact to 10% of the regular Foamular boards.

      1. Patrick_OSullivan | | #53

        > If you want to go through home depot, call up the pro desk at your local store and ask about special ordering Owens Corning "NGX". Supposedly they are able to order it, and that reduces the climate impact to 10% of the regular Foamular boards.

        The Pro Desk is "able" to order lots of things, but YMMV as to whether your local Pro Desk is actually helpful. Last time I tried this with another insulation product, they told me I had to order a pallet, which was many more sheets than I needed for the project in question.

        1. charlie_sullivan | | #56

          Well, if we share the order among the whole O'Sullivan clan, we ought to be able to make good use of a whole truckload.

  23. thegiz | | #50

    Thanks, I'm going to probably have to go that route. Just out of curiosity if I pay extra to custom make my eps with branch river and I bump up 25 psi to 3 pound or 60psi does that make a difference in how thick I could go with plywood? That 1 inch eps subfloor insularmor that dricore makes claims to be 70psi, which is why they claim you can place a finished floor right on top but as discussed there's nothing for fire resistance. I'm still lost on why they can sell it like that and even put it into installation instructions showing you how to place your finished floor right on top if you aren't allowed to do that by code. In their instructions they say for carpet you need 3/8 osb or spruce over foam. With the 60psi 1/2 inch foam and 3/8 plywood I would be doing the same thing as they suggest. I wonder if an engineer put in those specs or not. The psi of wood must be no where near 60 or even 100.

    I'm going to follow everyone's sound advice but thought I would put that out there. I can't help but over analyze, that's what I do.

    1. Patrick_OSullivan | | #52

      > That 1 inch eps subfloor insularmor that dricore makes claims to be 70psi, which is why they claim you can place a finished floor right on top but as discussed there's nothing for fire resistance.

      Can you please share where you saw that? The product page says "3,650 pounds per square foot", which equates to about 25 psi.

      1. thegiz | | #54

        Sorry they had a company called insul-armor with something similar to insularmor dricore. Apparently it doesn’t exist anymore, here is where I saw it:

    2. Expert Member
      Michael Maines | | #55

      25 psi foam will compress less than 15 psi foam, and 60 psi foam will compress less than 25 psi foam. This is not a standard installation so I don't know exactly how it will perform. Having walked on a lot of 1/2" sheathing on floors and roofs I would use 5/8" or preferably 3/4" so the edges don't compress and squeak when you walk over them. Or actually, as I mentioned, I would do a mockup if I was concerned about any details.

      I have never used foam denser than 40 psi, and that was only because a licensed engineer was a little nervous about an 18,000 lb point load on a 4' x 4' footing on 6" of foam, even though that's only 8 psi. I use 15 psi foam under slabs and also under "slabless slabs." (

      The framing lumber we use in the northeast has a compressive resistance of about 350 psi on the face (as opposed to end grain, which has higher compressive resistance but that never controls calculations). Sandy soil has a compressive strength of about 14 psi, and gravel soil's compressive strength is about 20 psi.

      I don't have an answer for why Dricore can sell that product. I emailed them to ask and they gave me a nonsense answer. I responded asking for the relevant code testing and have not heard back. I won't turn them in to any authorities but I would not be surprised if their product mysteriously disappears from the market at some point.

      1. Expert Member
        NICK KEENAN | | #59

        I think flooring over sleepers as in the "slabless slab" article is the way to go.

  24. Deleted | | #51


  25. thegiz | | #57

    So ran into a dilemma with cost. Since the price of sheathing is so high buying premade subfloor panels is not a huge difference in price anymore. The r+ panels by dricore are t and g osb with xps insulation on bottom. Obviously easier for a DIY but not sure if it's just engineered poorly and I would be better off doing the layers myself. Here is how cost breaks down:

    500 Square feet
    Dricore r+ panels- 7.87 per 2x2= 983.75

    1/2 inch foam 4x8 14.90= 238.40
    osb 19/32 4x8 32.65= 522.40
    Total= 760.80

    If I want plywood at 60.57 a sheet total project would cost= 1,198.40

    Also doing the layers myself I would need to but tape and tapcons but I'm assuming that's only $20-40 more

    1. Expert Member
      Michael Maines | | #58

      I just got this follow-up response from a sales rep at Dricore:

      "Hello Michael,

      "Below is the specific part of IRC R316 that pertains to floors. So, an Engineered Hardwood Floor product meeting this requirement should suffice. The best way to deal with this is to show the specific local inspector the material choices and the design of the assembly, and they will let you know. Each area will be different, we have found that with our other products. Hope this helps.

      "R316.5.13 Floors
      The thermal barrier specified in Section R316.4 is not required to be installed on the walking surface of a structural floor system that contains foam plastic insulation when the foam plastic is covered by not more than a nominal 1/2-inch-thick (12.7 mm) wood structural panel or equivalent. The thermal barrier specified in Section R316.4 is required on the underside of the structural floor system that contains foam plastic insulation when the underside of the structural floor system is exposed to the interior of the building."

      In other words, the flooring surface is supposed to be equivalent to 1/2" plywood as a thermal barrier, but some building inspectors will let it slide.

      Regarding costs, everything is expensive these days. Tapcons and good tape will probably be more over $100, depending on how much you need.

  26. thegiz | | #60

    Interesting is the code only referring to 1/2 inch plywood because of its fire resistance? Here is analysis of 7 flooring materials and there fire resistance

    Osb, parquet, hardwood obviously do best. Laminate was next in line. Engineered hardwood might meet the thermal barrier but the compression of the foam was an issue in the locking mechanism. Vinyl, pvc terrible, carpet was dead last.

    Could you glue 1/2 inch of cork on top of foam, or some other combo of wood and cork in that thickness? Compression wouldn’t be an issue because there’s no locking mechanism. Plus cork is eco friendly, already springy, and a natural fire retardant. Andy Engel used in as a basement finish in an article on here but of course he used plywood underlayment. I’m assuming there is most likely something wrong with this idea because no one has done it.

    DC I’m going to read that article

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