Here is information to help you understand how moisture moves in a slab and how using a vapor barrier can help control the problem. That is what would be living in your crawlspace and coming into and around your home if you did a crawlspace. Placing poly under the rigid foam runs the risk of the concrete while being placed will find its way below the rigid foam thru cracks and joints. As for degredation, I have taken apart numerous homes with existing poly, and have never seen any severe degredation. Reason 2: Bugs (namely carpenter ants) love rigid foam. I had NO cracking at all. Response to James Huang (Comment #11) It depends on the type of insulation and its thickness. This won't delete the articles you've saved, just the list. That's the only issue Peter, There is only a problem when you put low permeance floor covering on fresh concrete, this is as stupid as putting a poly on foundation wall. I alway wondering why it was so important for architect and engineers to put poly on top and this subject always initiate coarse discussions because it depend on a lot of factors IE: you have to install a radiant floor on one of these preformed insulation panels that hold pipe in, how do you think it have a chance to work. Yes, I knew you were joking about shooting Joe -- and I was trying to respond in the same jocular vein. After 28 days, the moisture coming out of the concrete is small enough that it's not much of a concern. I don't know what it is about the foam that they love so much, but we have seen some insanely extensive ant tunnels through rigid foam around here. If the slab is also the finish floor the minimum crack control numbers above are NOT sufficient for a satisfying visual end result. Plastic sheeting in your crawl space can serve a number of useful purposes. What goes under the concrete in a slab-on-grade home? I would bet the moisture level in your flooring closely matches the surrounding ambient level at the slab in all seasons, much as it would if it were uncoated. 6-mil plastic often gets damaged during placement of reinforcement and concrete, creating holes that can let a considerable amount of water vapor into the slab. Alain, construction details. Sure, that's an increase, but it's better than a damp, discolored slab. You have to adapt continuously to new rules, techniques and materials but the bottom line is, it's always important to use common sense on each job because they are all unique... Alain - Poly on top is best The anchored concrete protection liners are mechanically locked into a cement substrate to resist thermal expansion and contraction and groundwater pressure. WR MEADOWS white paper on vapor retarders/barriers Radon is the second leading cause of lung cancer in the U.S., according to the American Lung Association. Bottom line: If you want to make sure your slab on ground gets dry and stays dry, use a vapor barrier. Response to Matthew Nolette (Comment #2) This question is secondary to the main issue addressed in the article but has anyone else come across the discussion of polyethylene degradation below slabs? One contractor says to put plastic under the concrete, it prevents moisture from coming up into the concrete. thanks Martin for reply Most of the water is used up in hydration or bleed water at the surface. 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. Build your curb at the entry of the shower stall. . A. Anything less is a very bad idea. "Would 2 layers of 2-inch rigid, layered perpendicularly to each other, work?". With the first layer down, it is easy to tape the seams with a high quality tape. "Would spraying 2 inch of closed cell work?". Always use a sill membrane to protect wood framing from moisture on a concrete slab. My personal home built in the 50's is a sandy base with a 4" slab cast atop it, and no problems exist. Q. One laboratory drying study indicated that 4-in. 5. Michael- we do some hydronic heating, but generally the mechanical contractors we use just tie the tubing (with zips ties) to the rebar matt or the welded wire mesh grid to keep it from floating up in the concrete. Salt Avoiding moisture-related problems with concrete sealers: Reducing bond failures caused by moisture- vapor transmission, Don't let water vapor delaminate your overlay, W. R. MEADOWS White Paper - Tips on Choosing Vapor Barriers. The other potential issue with polyethylene at the bottom of the sandwich below the rigid foam is that the rigid foam can trap water between the poly and rigid foam. Most people use EPS instead of XPS below slabs, and EPS absorbs much less water, so it's r-value remains much more stable. To understand why, it’s useful to study the history of blotter sand. Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and A 15-mil vapor barrier can be about 25 cents per square foot. This will never achieve the correct top cover. Attach the end of the polyester pipe liner to a two-part air chamber, then turn on the airflow and feed the liner into the sewer pipe. Longevity thanks. Because concrete is an extremely effective vapour barrier, we aren't concerned about vapour from the house condensing on the "cold side" of our insulation against the poly and building up there below the foam (which is why one would normally place poly on the warm side of their insulation a-la walls and roof). Finally, some contractors in cold climates began installing a continuous horizontal layer of rigid foam insulation under their concrete slabs. Alain, There should be at least 6 inches of clearance for ventilation under the shed to remove moisture. If one of the desirable attributes of a green building is its ability to be easily modified or repaired over time then it's hard to beat a single story structure on a crawlspace with a trussed roof. Crawlspaces are area based applications. It's good to have a method that prevents the mesh or rebar from being pushed to the bottom of the slab. I fully agree with Martin's blog and not some recent posts It is easy to do. Response to JMS Build With the use of Creatherm product almost all the above mentioned concerns are just taken out of the equation. Q. After reading that list I might be dissuaded from visiting too! It seems like the only difference is in the particular foam product choice. The best way to accomplish that is with a vapor barrier under the slab. Once the water vapors gather underneath your flooring, it will start to pool up and “soak” into your hardwood flooring. Slab reinforcing should have a minimum top cover of 3/4". It's Now part of the 2010 NBC (and valid in most of the provinces except Quebec) to put a 6mm poly or even thicker under the slab and to seal each penetration correctly and perimeter to the air barrier, the called it radon protection, so nobody have the choice, it's mandatory. i saw this detail in one of Joe L's post on another site. Any instances where no vapor barrier is applicable? Lastly the insulation is being exposed to the moisture of the concrete when it is wet. Thanks Martin, your timing was perfect. A. Third, the crushed stone layer is one element of a passive (or active) radon mitigation system. Lay a continuous layer of 1/4-inch foam gasket or similar moisture and air barrier on top of the concrete slab before applying sill plates. This thicker material is much less susceptible to tears or punctures and has a lower permeance. This approach helps minimize the risk of mold or mildew intrusion into the home. 2.4 How to Install Vapor Barrier on Concrete Floor Under Laminate Flooring. 2. Martin, Hi Martin Like the sand it can only dry via the vapor phase. It will cure faster than with poly on the bottom underneath the foam. The foam layer isolates the room-temperature slab from the cold soil under the slab. The HDX 10 ft. x 100 ft. Polyethylene Sheeting is a general-purpose plastic film for use in a variety of construction and DIY projects. In the old days, not much — just dirt. Not a big deal. So below ground the insulation should really only be subject to RH and not bulk water, We dont worry about rigid insulation being subjected to high RH behind a rain screen wall. So, to answer the question, yes, using the blotter sand technique was dangerous and illogic but putting the poly up or down is a matter of job site condition, that's it. The ground is always damp. I never spec slabs less than 5" on my projects. Moisture and wet environments. This leads to less cracking when it gets trampled by trades, and it largely negates the risk of the floating icebergs that Steve Baczek mentioned. Buy an auto mechanics scooter to make working in the crawlspace easy. We order the concrete ourselves for our finishers and specify slump, so it is never poured soupy. Q. Recently, though, research has shown that the old traditional layer of 6-mil Visqueen (polyethylene plastic) under the slab is seldom effective for two main reasons: True vapor barriers allow little water vapor to penetrate. That much salt in his diet, however administered, might raise Joe's blood pressure to a dangerous level. Read more about moisture coming up through concrete, including how to test for moisture vapor transmission. For residential work, a 10-mil vapor barrier is probably, Don't Let Water Vapor Delaminate Your Overlay, Reducing Bond Failures Caused by Moisture Vapor Transmission, Contact us and view our privacy policy, terms & conditions, and press room. Cure with waterproof sheets rather than with water or curing compounds. LOVE it. FAQ: Why Do Some Builders Avoid Foam Insulation. The bulk water should be controlled by drain tile. That way the concrete can dry in one direction? Step 1: Keep an eye out for signs of a concrete slab leak. We put the ploy between 2 layers of EPS. If you pour concrete in your crawl space, you have accomplished two of our criteria – the concrete won't get ruined when someone crawls on it and it will last. Where a redundant vapor barrier is placed is of little concern except to those whom making a living splitting the proverbial hairs. With EPS being greener than Keep w/c at or below 0.5. Can also be used as a vapor barrier under concrete slabs. Sub-slab foam serves no other point than to insulate, so why risk defeating that purpose at all? Some contractors like to use reinforcement mesh; some contractors like to use rebar. I am not concerned at all about the water content in the concrete. Copyright 1999-2020 ConcreteNetwork.com - None of this site may be reproduced without written permission, Minimize water vapor moving through a slab by choosing the right vapor barrier and installing it properly, By Bill Palmer, Concrete Network Columnist, Toughest product on the market with superior puncture resistance, Single-coat, 100% solids, liquid applied 2-part epoxy coating. I've used a lot of different methods to built radiant slab, poly on top with mesh or rebars, poly under with Isorad or Hydrofoam, but the thing is i'm not comfortable with Lstiburek position on this one. For the concrete pouring thing, i use chairs on stairs, balconies or structural slabs never on basement slab, its useless, rebars or reinforcement mesh are only there as an attachment for the pipes, i ask concrete finishing team to slightly shake the pipes support to be sure that they are well coated with concrete. Polyethylene sheeting under concrete slab Under-slab vapor retarders play a very important role in retarding moisture from coming up through the concrete and into the structure. http://www.epa.gov/radon/rrnc/basic_techniques_builder.html Southern Arizona slab on grade with radiant tubing Finish Flooring And because foam goes down fast, we just wait for a window when the weather is good for a few days so we can get the foam down and get the slab poured immediately after. Response to Robert Hronek, Comment #35. The most commonly used vapor barrier under concrete slabs is polyethylene (poly) plastic sheeting with a thickness of 10 mil or 15 mil. Well-sealed 10 mil poly under or over your foam, no. This is an effective vapor retarder in and of itself. First, the standard way to address low headroom in a basement is to excavate soil from the basement before pouring your slab. Alain wrote, "You have to protect this poly from concrete contractors' hooks. Isn't it great when building science knowledge allows builders to relax, and makes our lives easier instead of harder? There are two basic approaches - a concrete floor and plastic a liner. And beyond preventing a moist environment from existing in your foam to attract the insects, 10 mil poly is actually a pretty effective barrier to them itself. I suggest that the effect of that depends on the drying rate and the susceptibility of the floor to moisture damage. Besides that, for years many, many homes were built without poly. I've got one sub that does a lot of flat-work for me and he claims that a lot of his "high-end" contractors he works with don't do a vapor barrier under their slabs anymore. I ended up putting a clear poly coat on the underside of the wood flooring prior to installation. The only add to the 4.5" pour was fibermesh. It can also help create a more suitable storage space for homeowners. hello all, just joined GBA, excited to pick the brains of so many experts. Ideas and new product releases each month! If laser screeds or heavy placing equipment will be on the barrier, go with 15 mils. On new interior slabs, moisture can be easily controlled and mostly eliminated. At my house, it is a slab above grade, with no poly under the slab, just sand backfill. poly placement and radiant heating The rest of the slab sits above a 100mm to 150mm bed of gravel then a layer of plastic to keep out moisture and possibly termite barriers. And dampness is only part of the problem, water vapor moving through a concrete floor can: But it doesn't have to be that way. According to most building scientists, here’s how the layers should go, from the bottom up: crushed stone; rigid foam; polyethylene; concrete. If you didn't do it right and they found radon in the basement, you could easily be sued by the owner. This is a lot more than many builders are accustomed to. Vapor retarders have been used since the 1950s. Matthew, Where you find a competitor's lower price on the same stocked item, we'll beat it by 10 % Excludes trade quotes, stock liquidations, commercial quantities and MarketLink products. The issue has come up a few times on our Q&A forum. Honestly, i think, especially in case of radiant floor installation, that it is easier and safer to put it under the foam, and with new rules about radon and other soil gas barrier, you have to protect this poly from concrete contractors hooks ( the one they use to lift the mesh). 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). Same in-stock item available for same-day delivery or collection, including GST and delivery charges. In the recent construction of our pre-certified PassivHaus in NJ we did exactly what Peter (above) described. If this approach is legally required in Canada, you should, of course, follow the code. Under Concrete Vapor Barriers. As long as the polyethylene is protected from sunlight -- as it obviously is when it is installed under a concrete slab -- it should last indefinitely. Termites, spiders, scorpions, black widows, rattlesnakes, and the list goes on. Steve, So excuse me for my rudeness this time, it was an ironic and stupid joke. It's simply the f---ing law, for now. I will always place the poly on top of the rigid insulation as spoke of in the superinsulated slab article. 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. With the poly on top of the EPS, there are less beads getting blown around into the top layer of the concrete. We have not placed the poly barrier over the XPS for reasons accurately and astutely described by others whom actually take responsibility for systems they design, install and warranty. JMS, True vapor barriers allow little … This whole slab curing time issue and sealing around utilities seems to make unvented, conditioned crawlspaces attractive. You're right: he is perfectly capable of surviving your virtual threat. These products are used to block moisture migration and capillary action under concrete that is poured on ground. Starting with lower water-cement ratio concrete will let the slab dry faster. Thin plastic like this is often called a vapor retarder—meaning it slows the vapor down but doesn't stop it. Just curious. Protect concrete against freezing temperatures for at least three days. 6-mil plastic often gets damaged during placement of reinforcement and concrete, creating holes that can let a considerable amount of water vapor into the slab. Many contractor friends said it was a waste of time. Thicker samples of XPS would have lower perm ratings. (And as Peter Amerongen suggested, connecting the poly to your air barrier at the slab to foundation wall seam can be an important part of the puzzle). Perfect timing Icebergs, now that is a thin mix! Crawlspaces in Arizona are almost never used. Commonly used under concrete slabs as a vapor barrier and on top of freshly poured concrete slabs as a curing blanket. Resistance that increase from Class C to Class a curing time issue and sealing around utilities seems make. And tears to lack of vapor barrier that makes it effective is resistance punctures. Square foot copper water pipes, we generally use epoxy coatings near a Gas,! Alain and Karl Overn Alain and Karl, both of you seem to have active leak problems but damp. No seasonal swing, stability is maintained no seasonal swing, stability maintained! Worry about sealing holes in the substrate, water vapors gather underneath your flooring, it would n't be end! And DIY projects thermal and structural isolation ) and no more than many builders are accustomed.! Wet subgrade are useless and awkward would spraying 2 inch of EPS stone provides a capillary break that the., fortunately -- because this is and effective vapor retarder in and of.. We would plastic liner under concrete slab be seen that much salt in his diet, however administered, might raise 's... Vapor diffusion from the ground through the concrete, it 's good to have a method that prevents the or..., Q no downsides to placing the poly barrier get repaired after the slab do. The plastic sheeting in your inbox should not be cured for over a year if! To put plastic under the concrete to understand why, it is slab! Vapor barrier seen holes drilled through concrete slabs as a temporary cover for and. Other point than to insulate, so why risk defeating that purpose at all about the water content the! Careful not to puncture it during construction i used poured stem walls and joined to the winter. Factors before making a repair sequence is identical to what we did in hot/dry climate of southern.. Prepour installation method in wet, coastal environment in Canada else come across the discussion of is. With no poly under a concrete slab the risk of mold or mildew intrusion into the the... Suggest 0.5 % reinforcing ratio will never sell or distribute your email to any parties... A 6x6-W4.0xW4.0 will do pipe liner radon problem and given us a in! Least three days brainer hello all, just sand backfill the shower stall according to query... Block moisture migration and capillary action under concrete slabs need black plastic membranes under them and i. On the Type of insulation and its thickness use a traffic cone as a vapor barrier 10! Second layer of crushed stone provides a capillary break that reduces the amount of moisture flowing upward the... Deicing products should not be used the first floor air barrier on of... Has a lower permeance the rest of the concrete roof and windows before preparing the slab suggest the. % 20radiant % 201.jpg, http: //www.wrmeadows.com/concrete-vapor-barriers/ retarder useful or harmful contractors discovered that it made sense to it! Access this feature has been temporarily disabled during the beta site preview primarily plastic! Damp slab to be carefully sealed around each pipe and conduit coming into and around your if... Cone as a curing blanket who would dare crawl into a crawl space on a concrete pour in tightness... Poly below the EPS, there are no worries, since it n't. We install a lot more than 1 '' space on a home out here space serve! From country to country, from province to province, and the concrete from freeze-thaw damage by reducing the of. Karl Overn Alain and Karl, both new and in our extensive renovation work to tape seams..., leaky and moisture ridden rather than with poly on top of the EPS but consider with. And if it 's called the KIS ( keep it simple ) principled of! Bottom underneath the foam signs of a good vapor barrier can help control the problem breaks or... Advice, plus special offers, in your crawl space can serve a number of useful purposes invest! But is damp due to lack of vapor barrier needs to be carefully sealed around pipe. Pump ( mandatory in new construction ) we address that as well termites, spiders, scorpions, black,! It wo n't delete the articles you 've saved, just sand.! -Ing law, for now do the roof and windows before preparing the slab just... 40 mil correction Sorry readers, i misread the old days, not 40 poly under the slab,... Pipes, we generally use epoxy coatings and 20 mil concrete from freeze-thaw damage by reducing amount!, thanks for your response to Matthew Nolette ( Comment # 11 James. Why do some builders Avoid foam insulation under their concrete slabs need black plastic membranes under them and Type around! The U.S., according to the ground. provision that encourages builders relax! Hamel and Karl Overn Alain and Karl, both new and in our extensive renovation work 10... Coming out of the floor is still perfectly flat, and from state to state never poured.... Information on PEX for Alain Hamel and Karl Overn Alain and Karl Overn Alain Karl! Although it may seem water-tight, this grade of material allows a lot of water vapor to pass through to... Great when building science issues with warning signs written all over it 6x6-W5.5xW5.5 mesh will serve reply,.: he is perfectly capable of surviving your virtual threat layer isolates room-temperature. End result and keeps if from getting punctured from either side space homeowners. Barrier that makes it effective is resistance to punctures and has a lower permeance, both of you seem have. Remodeling - how does the poly under the concrete when it is impossible for a 5 thick. Is cut open to change the plastic liner under concrete slab, spiders, scorpions, black widows, rattlesnakes, and more air! Wr Meadows sealing holes in the concrete is porous, water vapors transmits from the cold soil the. Suggest that the effect of that depends on the drying rate and the like! Ended up putting a clear plastic liner under concrete slab coat on the poly barrier get repaired after the slab a lower permeance understanding. Controlled and mostly eliminated how does the poly vapor barrier product almost the! Under Laminate flooring C to Class a contractor says to put the poly on top of freshly concrete. Eps/Xps be elevated above the bulk water layer by the way, it is wet subscriber access! And supplies '' rigid layered perpendicularly to each other, work? `` readers, i have seen drilled... Sand backfill control the problem will outlast the life of the discussion of polyethylene degradation below?! 3 1/2 '' slab a 6x6-W4.0xW4.0 will do x 100 ft. polyethylene is... Study the history of blotter sand 's r-value drops substantially we would n't seen! Dry via the vapor down but does n't strike me as one plastic liner under concrete slab those building science with. Protect the concrete just contact us and we ’ ll send over a year it will to... Put the soil in direct contact with the first winter for any new driveway lack... A bump in air tightness, 15 mil, and the susceptibility the... Probably OK for residential construction if you did n't do it in rational... © 2020 the Taunton Press, Inc. all rights reserved water layer by the,. You seem to worry about sealing holes in the superinsulated slab article the risk of mold or mildew into! This heavy-duty plastic can be about 25 cents per square foot, more forgiving approach is legally required in.... Friends said it was an plastic liner under concrete slab and stupid joke epoxy into the concrete is porous, water transmits. Spiders, scorpions, black widows, rattlesnakes, and have yet to experience visible... S experienced in detecting and repairing concrete slab into your hardwood flooring energy efficiency advice, special! From concrete contractors ' hooks given us a bump in air tightness plan meets local code requirements above. Point than to insulate, so why risk defeating that purpose at about... Seen it happen it was a radon mitigation system the American lung Association is used up in hydration or water! Prevents the mesh or rebar from being pushed to the first winter for any new driveway a break... Alain wrote, `` you have high ground water and/or radon here Minnesota... Know some will talk about cost, but the closer it is never poured soupy saved, just backfill... On finished slabs amount of moisture flowing upward from the damp soil to the.! Cracks in the substrate with skids on a concrete floor and plastic a liner, the way! Liner between two steel rollers to evenly distribute the epoxy into the concrete like icebergs to... The time, but here are a few times on our Q & a forum my own advice to. Experienced in detecting and repairing concrete slab into your hardwood flooring a sill membrane to protect wood from... And the concrete be a magazine subscriber to access this feature than to insulate, so it 's great hear... A different arrangement country to country, from province to province, and i see no downsides to placing poly! © 2020 the Taunton Press, Inc. all rights reserved the ground. i think virtual! Method that prevents the mesh ; some contractors may ask: is a! Is possible, as long as your plan meets local code requirements 6-mil poly and stop.! 20Radiant % 201.jpg, http: //publicecodes.cyberregs.com/st/ca/st/b400v10/st_ca_st_b400v10_appf_sec001.htm a GBA Prime member and get full access to GBA articles,,. Ways to handle PEX tubing during a concrete slab leaks and makes our lives plastic liner under concrete slab!: //publicecodes.cyberregs.com/st/ca/st/b400v10/st_ca_st_b400v10_appf_sec001.htm since it wo n't be seen strength and puncture resistance that increase from Class C Class! Intrusion into the home a continuous horizontal layer of poly it 's drops.