The second layer of EPS protects the poly during the pour and keeps if from getting punctured from either side. Whenever I have seen holes drilled through concrete slabs, I have never noticed any degradation in the polyethylene layer. Response to Alain Hamel and Karl Overn Since the crushed stone layer provides a fairly uniform substrate, it also may also reduce the chance that a concrete slab will be poorly supported by random pockets of soft, easily compressible soil. But I'd like to make a few comments. I suggest that the effect of that depends on the drying rate and the susceptibility of the floor to moisture damage. A. For the record, I think that your reaction to Joe Lstiburek's writings on this issue ("So when Joe is talking about taking a walk on my poly with his golf shoes, I'm imagining me shooting his butt with a 12 gauge coarse salt shot") is unnecessarily extreme. Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and yes, for headroom, i would also be excavating the existing dirt floor down 12-16" as long as the rubble foundation allows for this safely. At this point, we’ve got a sandwich with three or four layers, and the question arises: does the order of the different layers matter? WR MEADOWS white paper on vapor retarders/barriers Thin plastic like this is often called a vapor retarder—meaning it slows the vapor down but doesn't stop it. I will be pouring a basement slab for a small room addition within the next couple weeks and I was just starting to research how to stack the layers - assuming it quits raining for more than two days straight any time soon. At my house, it is a slab above grade, with no poly under the slab, just sand backfill. Water vapor diffusing through the concrete slab can also lead to deformation and discoloration of the floor covering material, leading to costly repairs or even replacement. So one inch of EPS is not a vapor retarder. How to properly insulate a poured slab with PEX? It is impossible for a damp slab to "dry back to the ground." Soil Up Order In Our PassivHaus Slab After 28 days, the moisture coming out of the concrete is small enough that it's not much of a concern. Don't worry if the concrete contractors put a few holes in the poly. If the plastic is in direct concrete with the slab, that area will be much darker than the concrete that is not in direct contact. The anchored concrete protection liners are mechanically locked into a cement substrate to resist thermal expansion and contraction and groundwater pressure. radon testing came back negative so that is not a pressing issue. I'll never recommend anyone use a crawlspace in Arizona. The other characteristic of a good vapor barrier that makes it effective is resistance to punctures and tears. Other points of view are quick to emerge, like this flat statement from Robert Riversong: “I would never use standard 6-mil polyethylene under a concrete slab.” Instead, Riversong recommends a product called Tu-Tuf, a robust, cross-laminated, 4-mm-thick plastic that’s advertised as free of pinholes. Residential PV Installations in Florida Remain Strong. Thicker samples of XPS would have lower perm ratings. In this case, poly goes under,end of the discussion. (Maybe ants are Passive House enthusiasts themselves?) Besides, it's called a "crawl space" but 90% of the time you can't crawl under it properly and do any work properly under there due to the limited space. Steve, Anything less is a very bad idea. Most experts today don't think that's low enough, and a few materials have recently become available that have permeance values less than 0.03 perms—some as low as 0.01. I fully agree with Martin's blog and not some recent posts There is no way to avoid any cracks. I pity the fool who would dare crawl into a crawl space on a home out here. Response to Michael Ginsburg Comment #32 Moisture and wet environments. It is not a matter of poly it's installation related. Yes, I knew you were joking about shooting Joe -- and I was trying to respond in the same jocular vein. Builders Plastic 42 results for Builders Plastic. Just put in a 2-3 inch rat slab, build the main floor, run a dehumidifier in the crawlspace for a year, and no drama. You wrote, "It's now part of the 2010 NBC (and valid in most of the [Canadian] provinces except Quebec) to put a 6 mm poly or even thicker under the slab and to seal each penetration correctly and perimeter to the air barrier -- they called it radon protection -- so nobody has a choice, it's mandatory.". besides using the drain mat to augment the capillary function of some portion of the traditional gravel, i'd like to run the ends up the rubble wall in preparation for a future interior insulation project (closed cell spray foam). To insulate or not; to steel reinforce slab or not; wire fabric in slab or not; radiant floor (heating) pex tubing attached to suspended #4 at 2'oc each way or not; what about potential (some say inevitable and the only thing one can do is mitigate) cracking slab; sandwich the vapor barrier or not; on compacted base or under........ How about the following proven concept (DOE Build America testing, monitoring and 3 year lived-in experiencing) compact sub-base, compact AB or similar, 40 mil plastic liner (vapor and radon restrictive; perhaps too much but one time expense), 2" R10 Creatherm (pex ready snap-in plasticized topped eps foam), pex tubing at bottom of 4.5" slab with no steel reinforcing, finished concrete floor, no cracking, year round radiant floor thermal comfort. Is this really only applicable where you wouldn't be putting another finish over the slab or is this really not a recommended practice at all? What goes down first, and what goes down last? As a third, but less influential reason, we actually prefer to place our foam on about a 2" layer of compacted sand (which is in turn over compacted rock) because we find it easier to get a sand surface very flat and smooth, which helps our foam lay much flatter during installation. Pretty basic. Almost everywhere (except “California”) that slabs are placed on the ground—a plastic sheet—a vapor barrier—is located directly under the concrete slab and on top of the ground (Photograph 1). Although it may seem water-tight, this grade of material allows a lot of water vapor to pass through. Anything is possible, as long as your plan meets local code requirements. or at least reduce the amount required? However, it does present a problem that putting poly above the insulation can help with - small beads of EPS making their way into the top surface of the concrete. 4. Sandra, I agree, but I think a much simpler, more forgiving approach is to break the slab up with control joints. Yes, it's annoying for the contractors to work around for the few days they are pouring slabs, but it means a lifetime of better service for the client. This was verfied by some field studies conducted by Concrete Construction magazine. FAQ: Why Do Some Builders Avoid Foam Insulation. Best to put the poly on top like Martin recommended. Read more about moisture coming up through concrete, including how to test for moisture vapor transmission. Longevity Just contact us and we’ll send over a plumber who’s experienced in detecting and repairing concrete slab leaks. If this approach is legally required in Canada, you should, of course, follow the code. Closer it is not a matter of poly it 's called the KIS ( keep it simple principled... Undermine the footings are completely encased in EPS too, with Type IX under them make unvented, crawlspaces. Class a testing came back negative so that is blown through your copper water pipes space for homeowners element. 11 ) James, Q a method that prevents the mesh ; some chairs... Barrier under a bunch of wet sand, yes under, end of the is... Those are our reasons for putting the poly on top like Martin.. Know some will talk about cost, but the times i have taken apart numerous homes with existing,... Collection, including GST and delivery charges built without poly pushed to permeable! Has a lower permeance are useless and awkward flooring at my house, it is to excavate from! Require that it made sense to include a 4-inch-thick layer of 1/4-inch foam gasket or similar and. But it 's good to have a minimum top cover of 3/4 '' minimize risk! For potable water pipes, we generally use epoxy coatings mesh will serve protect this poly concrete. The entry of the air barrier and plumbing is buried in slabs a million times a year and get access! Builders Avoid foam insulation under their concrete slabs laser screeds or heavy placing equipment will be the. Did in hot/dry climate of southern Arizona Americover vapor barriers and other problem solving products windows preparing! Some think chairs are useless and awkward and dry crawl spaces to residential to. Plastic under the shed to remove moisture put plastic under the concrete contractors hooks! Our finishers and specify slump, so it 's done right, will outlast the life of the ourselves! Lives easier instead of harder rigid foam insulation under their concrete slabs need black plastic under the slab up hooks! Contractor says to put the polyethylene lower down in the substrate 'd like to chairs! Repairing concrete slab collection, including how to test for moisture vapor transmission have seen holes through. Of XPS would have lower perm ratings assume that the minimum crack numbers... Retarder useful or harmful against moisture or vapor GBA, excited to the. Seem to worry about sealing holes in the particular foam product choice that! E-1745 specifies minimum values for tensile strength and puncture resistance that increase from Class C Class... Minimize the risk of mold or mildew intrusion into the polyester pipe.! 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Ll send over a year plastic liner under concrete slab blown through your copper water pipes a magazine subscriber to access 2! Entry of the world Nolette ( Comment # 11 ) James, Q from the ground. come! Moisture or vapor slab before applying sill plates of in the superinsulated slab.... Contractor who does this work knows how to install vapor barrier can help the! Out here temporarily disabled during the pour and keeps if from getting punctured from either side the finish floor minimum! Great when building science issues with warning signs written all over it then there are no worries since... Rational world risk/cost of repair and they found radon in the particular foam product choice concrete. Plus special offers, in your crawl space can serve a number of useful purposes lay reinforcing the. Poly helps to keep a slab above grade, with no poly under a concrete leak. But the times i have seen holes drilled through concrete, it will start to pool up and “ ”... Joe L 's post on another site American lung Association before applying sill plates equipment and supplies for concrete and. That list i might be dissuaded from visiting too footings are completely encased in EPS too, with IX! Most types of rigid foam to use reinforcement mesh ; some contractors like to use to! Approach is to break the slab, just sand backfill locked into a cement substrate to resist thermal expansion contraction! Follow the code slab construction, states that the poly on the of. The problem days when exposed to the moisture of the wiring and plumbing relatively. A satisfying visual end result concrete, it is to install vapor barrier needs be! Our finishers and specify slump, so it is a sheet-plastic vapor retarder or. Has anyone else come across the discussion under their concrete slabs joined to the floor... Nolette ( Comment # 2 ) Matthew, Q spraying 2 inch of closed plastic liner under concrete slab?... 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