Is Vapor barrier needed behind Durock when using Kerdi membrane?
eesutton
14 years ago
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pepperidge_farm
14 years agoUser
14 years agoRelated Discussions
Am not getting the vapor barrier thing, at all?
Comments (20)"He (GC) says that any water wicking through will have no chance to dry out if it becomes trapped by the vapor barrier, and you increase the chances of mold growing between the vapor barrier and cement board. This makes sense to me!' How can mold and mildew form and thrive between poly sheeting and cement board? Mold and mildew need food to survive. That food it cellulose. Cellulose is wood or wood-derived products like paper. Paper facing on kraft-faced insulation, paper facing on drywall, etc. Moisture trapped between a 6-mil poly vapor barrier/drainage plane and the cement backer board has no cellulose in sight, so the green stuff can't thrive. The moisture will eventually dry out back into the bathroom, just as Bill described. No poly vapor barrier? Then when the moisture gets behind the cement board and wets the the kraft paper facing of the insualtion, or the framing, then you get the funky green stuff. Moisture, spores, and food equals the dreaded green funk. It's tough to get your head wrapped around these concepts, but trust me, the way Bill and others have said is correct. Your GC is wrong. He may have good intentions, but he's just uneducated. Building Science is a continually evolving process. Changes to the building code normally lag bulding science by as much as a decade. Sometimes even longer. Too many builders don't learn about or apply changes made to the code until several years after the code has been changed. Many "rotted wall" stories are from having vapor barriers behind greenboard. Trapped water and the paper facing food source on greenboard leads to the dreaded green funk, soon followed by the wetting and rotting of the gypsum core of the greenboard. But who here has been tiling over greenboard? Only the guys who like greenboard because it's cheaper than cement board and easier to cut and hang than cement board. Greenboard was allowed by code as a tile backer in wet areas until January of '06. Yet I've NEVER used it as a tile backer. Doing what's allowed by code isn't always the right way to build. Remember, code is the MINIMUM building standard. In some areas of construction the minimum is good enough. In other areas it's far below. That's why the code evolves. Mongo...See MoreVapor Barrier: Placement & Recommendation Questions
Comments (19)A vapor barrier protects the warmth and integrity of your home. Below was pasted from the internet. The friend is incorrect in his statement. New homes are very tight due to better barriers and very good sealing windows, but eliminating barriers causes bigger issues. Very tight homes you can leave a window cracked at times. Some newer heating/cooling systems have exchange systems built to pull in fresh air. I personally use poly sheeting as a vapor barrier because it is far superior to faced insulation. Regarding ceilings, check your local building codes, this may vary. But as mentioned below, attics can naturally ventilate as compared with a closed in wall. Through a process called convection, warm air will always move toward colder air, meaning that during the winter the air inside your home is always trying to escape the house and move toward the cold air outside. Warm air also expands, and therefore has the capacity to hold more moisture than cold air -- moisture that is picked up naturally from inside your house. As the air cools, it contracts and loses some of its capacity, so the moisture is given off to cooler surrounding surfaces. The result of all this is that warm, moisture-laden air is constantly on the move from inside to outside. As it leaves the warm interior of the house and enters the walls, attic, and crawl space, it cools off and gives up its moisture, which in turn can saturate the insulation and framing. The more moisture there is in the air and the more differential there is between the inside and outside temperatures, the worse the problem can become -- in the more extreme cases, the insulation is rendered virtually useless and severe rot can take place in structural members. It is the purpose of the vapor barrier to prevent that movement or penetration of moisture from one area to another. Placed between the inside of the house and the insulation, the vapor barrier acts as a physical shield to repel the moisture and keep it from entering enclosed cavities where it can do serious damage. Vapor barriers can be created from a variety of materials. The only requirement is that the material be resistant to moisture, which is indicated by its vapor permeance value, called a "perm" rating. To be an effective vapor barrier, a material needs to have a perm rating of 1.0 or lower. Common vapor barriers used with insulation include plastic sheeting, foil sheeting, and kraft paper that has been treated to achieve the proper perm rating. Vapor Barriers in the Home One of the most important vapor barriers in the home is the one between the wall insulation and the interior side of exterior walls. Because wall cavities are sealed and have no means of allowing accumulated moisture to escape, an effective moisture barrier is crucial in preventing warm, wet air from entering the walls. For wall insulation, foil- or kraft paper-faced insulation is typically used. The insulation is installed between the studs with the vapor barrier facing in toward the house -- the one thing to remember about vapor barriers is that they are always installed between the insulation and heated portion of the house. The "wings" along the edges of the insulation are stapled to the studs to hold the insulation in place -- stapling to the face of the studs instead of the sides creates a more effective vapor barrier. Another alternative for walls -- which is also commonly used in the enclosed cavities of vaulted ceilings where the pressure of warm air trying to escape is even greater -- is to place unfaced insulation into the cavities between framing members and then cover the insulation on the inside with plastic sheeting. The sheeting is stapled to the face of the studs or joists, and overlapped at all seams to prevent moisture penetration. In today's construction, separate vapor barriers are typically not used between the home's interior and a ventilated attic. Most attics are insulated with blown fiberglass, which is relatively porous in comparison to the denser batt insulation used in the walls. The attic also has a continuous flow of air through it that is created by the roof and soffit vents, so moisture from inside the house passes through the insulation and is removed from the attic by the air currents. In areas of high humidity where moisture in the attic could still be a problem, a vapor barrier paint can be applied over the inside ceilings. Another area that typically does not have a vapor barrier is the floor. Most of today's homes are now constructed with subfloors of interlocking tongue-and-groove plywood or other sheet materials -- waterproof resins are used in the making of the sheets, so the subfloor itself becomes an effective vapor barrier that protects the insulation below it. A vapor barrier is used, however over the ground under the house. Typically a layer of 6-mil plastic (1 mil = 1/1000 of an inch) that is laid directly on the dirt floor of the crawl space, the moisture barrier prevents ground moisture from entering the enclosed crawl space and wetting the insulation or the framing....See MoreContractor doesn't use vapor barrier behind tiles in tub
Comments (10)Hi Jenna - Your contractor has been doing it wrong for years -- many have... Hardiebacker and Durock are more water-resistant than ordinary sheetrock, but they are certainly not waterproof. If you ever see a scrap of Durock that has been left outside in a wet environment for a few weeks, you'll see what I mean. In a finished shower, moisture will go through the grout lines very easily, and even through the tile faces themselves to some extent. That moisture will seep into the Durock where it sits until it evaporates (slowly) or continues on to the wooden studs behind, causing them to rot. A moisture membrane behind the Durock helps slow this process down A LOT, preserving the life of the wooden framing studs behind. What's even better is a relatively new product called 'Kerdi' that's applied on top of the Durock. Do some reading on this board, and have your contractor do some research on Kerdi, and the benefits will become apparent very quickly. The over-simplified version is that Kerdi is a moisture membrane that goes between the tile and the Durock. The Kerdi layer prevents the moisture from ever reaching the Durock, dramatically lengthening the life of your installation. Of course, for leaks that occur at the valve, none of these precautions will help much... There are moisture alarms you can buy that will notify you if there's a leak, and leaving an access panel behind the valve will be invaluable then....See Moretime-critical question on vapor barrier behind cement board--help
Comments (4)I forgot to mention we are using a shower pan, so the floor isn't an issue. There are two walls that are interior walls and they don't even go all the way up to the ceiling. These are the ones under question. Should the cement board be pulled off and the plastic installed, should something else go over the cement board, or should we just take our chances? It is not particularly humid where we live and there is heated space on both sides of the walls I'm talking about. I truly hate these last-minute decisions! Is Redguard a membrane like a plastic or something you paint on? Is it expensive? How long does it take to apply and dry? Thanks for all the info I've learned here!...See Morecarydan
14 years agoMongoCT
14 years agocarydan
14 years agoMongoCT
14 years agoMongoCT
14 years agopepperidge_farm
14 years ago
weedyacres
14 years agocaybound
14 years agoMongoCT
14 years agodavidro1
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14 years ago
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