Any thickness of concrete slab is permeable to moisture through vapor diffusion. Radon, for example, is the second leading cause of lung cancer in the United States, and the leading cause among non-smokers. concrete construction, Vapor barriers have been associated with certain concrete slab-on-grade problems including curling and cracking. Sweating Slab Syndrome may not sound as dire as “Concrete Cancer,” but the results can be a big headache for building managers and a major liability concern for owners. Moisture will have a harder time moving through product inventory and its packaging and will instead begin condensing and pooling on the floor below, in the right (or wrong) conditions. Take the same foolhardy logic of the builder who removes below-slab vapor protection from the design of their warehouse or storage facility project and take it another step: what happens when the building needs to be reconfigured for another use? In temperate climates, we see no advantage to placing a vapor retarder beneath a sidewalk. This might be the biggest misconception when it comes to vapor barriers: their impermeability to moisture does not allow a newly-placed slab to dry evenly out of the bottom of the slab, as it does from the top. If you're in a cold climate and the subgrade soil is poorly drained, a vapor barrier might be marginally useful. Have the latest post sent right to your inbox. I'm trying to figure out how to put the vapor / moisture barrier under a monolithic concrete slab. When evaluating the performance qualities of vapor barriers as soil-gas retarders, be sure to check the radon diffusion coefficient of the material before you select it. All that to say,  4 inches of insulation is fine, but six likely wouldn't be overkill where you are if you wanted to beef it up a little.  Here is a DIY slab on grade installation video if you like, and if you are interested let me know, Legalett distributes all over North America.Â, The DELTA®-DRY & LATH is a 2-in-1 product combining the microporous DELTA®-DRY …, ISOCLAD | Air barrier insulation panel for above grade exterior walls, Aerovap Hygromax moisture regulating watertight membrane for building construct…, Air barrier spray to reduce air leakage in homes and commercial buildings, Crawlspaces are becoming rare for new home construction in USA & Canada. As a final thought as well, remember that radon isn't only going to enter homes fromt the soil, but radon gas in water is another potential source that should be considered to ensure safe indoor air quality in a home. Air barriers need to be continuous and free from holes, but vapor barriers do not need to be. Photo courtesy of Chavez Concrete Contractors, Inc. I’m under the assumption that a rat slab mainly has the following benefits: 1. here as the water evaporates in a process known as, are the white, flowery blemishes you often see in concrete. Concrete Curing Issues For an under-slab vapor barrier to be most effective, it should be in direct contact with the underside of the slab. An error occurred. The flooring says I need a vapor barrier under the underlayment, the underlayment states it has moisture protection but not a vapor barrier,the little picture shows moisture from above see photo. If you have an older home that may not have moisture barrier protection under the concrete slab, you can still add a barrier to protect your vinyl floor from bubbling. This can increase the flexibility and desirability of a site for a potential buyer with designs on converting the facility for a different purpose.5. A below-slab vapor barrier can also help prevent sub-slab radon ingress. The water added to the cement, sand and aggregate mixture is necessary to form a good bond in the concrete, but it is also necessary that the moisture evaporates away from the concrete in order to let the concret… There is no way to test radon levels in a home before it is built and no way to install a barrier after a slab is poured, so I’d certainly install a radon barrier it if I were you since you are building in a high-risk area. mop or a “wet floor” placard may be a temporary solution – but the saltiness (the efflorescence) doesn’t evaporate with the water. If you've got a crawls space with damp, mold, odor & cold issues, here's how to insula…, Removing radon gas from existing basements and crawlspaces can be very effective, here are different options for different situations. Of the relatively few builders that seem to be are aware of radon gas health issues, many will just use a standard 6-mil poly vapor barriers as a radon barrier, which is better than nothing, but I’d want a thicker one for my home. By forgoing the installation of a below-slab vapor barrier, you ensure a greater amount of moisture entering the building from underneath your building’s foundation. And for installation, if you can, lay the barrier down BETWEEN layers of foam, that way you walk on it once and then cover it. A high-performance vapor barrier prevents long-term curling. However, the far greater risk to a slab is long-term curling over the lifetime of the concrete foundation, which a high-performance vapor barrier helps prevent. This will provide the placement team better results and happier customers. Choose carefully between Polyisocyanurate, EPS & XPS or Mineral Wool & Hemp as the wrong choice can reduce insulati…, As so many searches are done online for Radon Gas Maps, Radon Gas safe levels and Radon Maps by State of USA or Province of Canada - We decided to stress the i…. This water destroys the bond and the barrier fails. If the slab is built over a layer of gravel with a sub-slab vapor barrier, then the basement space will be a lot dryer. The more your HVAC system is working, the more money you are paying in electricity costs. The thicker polyethylene-polyester blend is much less permeable to moisture than the 6 mil. Chances are – replacing them will be much more expensive than installing that high-performance vapor barrier in the first place. This is done because the concrete itself is not a good moisture barrier. There are many products available in home centers and hardware stores in liquid form that can be used to cover and protect the concrete slab from the top. Choosing to install a high-performance vapor barrier in your design will save you from headaches and more expense in the future. That accumulation of water can destroy sensitive products. 4 inches of EPS rigid insulation can meet code requirements as a vapour barrier only if it is overlapped, to make sure moisture does not pass through the butted joints if you are only installing single sheets. Vapor barriers are used because while fresh concrete is poured wet, it's not supposed to stay that way. This can be a time-saver where the placement team has a predictable surface on the site throughout. Sorry for the inconvenience. installation, To continue about radon – exposure to radon gas in homes is the second greatest cause of lung cancer. One of the classic mistakes builders make in storage facilities and warehouses is the impact moisture vapor can have on expensive inventory that must be replaced if damaged. Ok Mike, thanks for the great response and suggestions. Even an excess of moisture that was retained from the original concrete mixture will cause problems if the slab was sealed prematurely. Install the proper type of vapor barrier siouxland homes why a plastic vapor barrier under concrete slab mondays with vapor barriers in concrete foundations networx are vapor ers necessary for bats and garages install the proper type of vapor barrier siouxland homes under slab vapor barriers done right professional builder. Many of those salts are. What does some extra moisture vapor really matter? Furthermore, placing concrete directly on the vapor barrier’s consistent surface can make finishing of the slab more even. While there are many factors to consider, a general rule of thumb is: the lower the radon diffusion coefficient, the better. But they have also proven to be beneficial in reducing failures of moisture-sensitive flooring materials, adhesives, and coatings caused by excessive emission of moisture vapor from concrete slabs. Any home that is built on a concrete slab is going to need to have a vapor barrier installed. Installed over an on grade concrete slab. This moisture deposits on the surface of the slab and causes damp and slippery conditions. A 6-mil (0.006 inch; 152 µm) polyethylene or approved vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the concrete floor slab and the base course or the prepared subgrade where no base course exists.. R506.2.3 Vapor Retarder. All of the problems associated with moisture vapor movement in a concrete slab will go away in time as the slab dries, as long as there is no … Liquid water below the slab can diffuse through the slab as vapor, then condense under the flooring, which can emulsify some adhesive and destroy the floor covering. Keep that mop or placard handy. One of the critical ways many HVAC systems work in buildings is by removing moisture from the air and reducing the relative humidity of the building envelope. Will it stay attached to the concrete? Also confused, is which one is more impor…, Rigid foam insulation boards are different. Concrete is porous and water vapor will eventually come through the slab. Many concrete sealers may prevent the intrusion of water but not water vapor. If you’re using Portland cement concrete, you will have alkaline salts in the slab. Without a vapor barrier, moisture would continually wet the bottom of the slab, as vapor will continuously drive from the high humidity below slab to the relatively low humidity above the slab. The peril of ignoring below-slab vapor protection in your building does not begin and end with the floor covering and its inhabitants. I might add that a vapor barrier under the slab also contributes to slab "curl", where the top of the slab evaporates quickly, but the bottom does not. ASTM E 1643, "Standard Practice for Installation of Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs," provides details, but here are a few tips: Most exterior slabs do not need a vapor barrier. We're soon building a slab on grade foundation for our new cabin in Montana and I've decided to sit it on a 4" EPS foam insulation so the slab will retain some passive solar heat from the south facing windows in winter, avoiding having to put too much heat in to keep stuff from freezing. 9. This is a far greater curling threat to the foundation, long-term. Do I just put the plastic down and drape it over the form, and then cut to ground level when done (like the red line in the picture)? In my situation, the benefits seem rather minimal. Without a high-performance vapor barrier, installing a floor covering may be impossible (or violate its warranty – more on that later). The gasket must be … The next time humid air hits the slab in your facility, the slab will “sweat” again. No it cannot. energy efficiency, The penny-wise and pound-foolish may think forgoing the installation of a vapor barrier can save them time and money. Actually, no. Resources for Contractors and Distributors for Stego Vapor Barrier Products. By opting to save relative pennies in material costs, some project designers, contractors and building owners are electing to ignore industry best practices. It might just be the smell of ignoring the need for below-slab protection. Underlayment with 6-mil Vapor Barrier. Water and moisture will pass through a concrete slab that does not have a vapor barrier with little trouble. http://www.AsktheBuilder.com founder Tim Carter describes a vapor barrier that's underneath a concrete slab that's about to be poured. Thoughts please? Those are the white, flowery blemishes you often see in concrete.