What To Use As A Vapor Barrier in Attic Using Rock Wool
chipster_2007
14 years ago
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Vapor 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 Moreinsulation and vapor barriers
Comments (6)Back in 82, my husband I, newlyweds at the time, rented a large 5 bedroom house built in 1900. We were told how well it was insulated and our heating bills would be no more than $80 a month. I was 22, hubby was 24. What do you know at that age? lol...nothing...anyway, imagine my gut wrenching distress when our first heat bill came....and we hadn't lived there yet! We still had a lease on an apartment that we had to satisfy in order to move into this place and the owner of the old house wouldn't let us wait till the other lease was up to sign her lease. Anyway, the first bill was over $300 and the heat was set at 55 degrees. After my husband came home from work and found me crying hysterically outside, we called the landlady. We drove to her house and told her what we were told by the broker she had hired to rent the thing and what was in actuality a lie. And a big one at that. She agreed to pay that heating bill and to have insullation blown in. Now fast forward 23 yrs and who owns the house now? My sister. Very weird, but that's another story..lol...anyway, in answer to your question, she has no mold or mildew anywhere in her home. She has had to gut 2 rooms and the insulation and everything within the walls, were still packed tight and looked great. My dad and I blew in cellulose this last winter and I'm sure it's too early to tell, but I don't anticipate any problems based on my sisters house. Terry...See MoreWhat to Use: Faced or Unfaced Mineral Wool Insulation
Comments (9)Does the reflective facing really offer any more heat retaining/reflecting value? no. for reflective surface to reflect, it needs a minimum of 3/4" or larger air space to work. facing the reflective surface down..(as in vapor barrier to warm side).. puts reflective surface on attic floor. facing reflective side up..would work in hot climates as a radiant barrier..but only until dust buildup reduced reflectivity. I used fiberglass batts in my attic. all unfaced. first layer in joist bays, second layer across joist bays. just what I did in my own house. before adding insulation, air sealing attic floor to living space below is a good investment. if you minimize air flow through insulation, it will perform to its rated R-value. caulking wire penetrations, plumbing penetrations, sealing around vent fans for baths & stove vent penetrations all help. if your ductwork is in the attic you should seal ductwork prior to any added insulation. it is much much easier to work in attic prior to insulation. it will never be as easy again. where are you located? I'm interested in what you chose and why. if you don't mind sharing. for further reading on vapor barriers here is a link to a blog that has some great info. peruse some of the earlier postings also. http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/54110/You-Don-t-Need-a-Vapor-Barrier-Probably best of luck....See MoreBlown in Fiberglass or Cellulose in walls with no vapor barrier
Comments (12)"Mostly heating, but the house does also have central air." How many degree days of heating? degree days of cooling? PA is all over the place. Typical winter low? Summer high & humidity? All these things come into play. In many parts of the the US a vapor barrier is not actually doing anything much. It can only be on one side of the insulation, and with relatively equal heating and cooling loads should just be omitted. Frost freezing in cold attics is a very cold weather occurrence. It simply does not happen in the more temperate areas. One of the problems we have is trying to establish energy codes that cover insulation and things like vapor barriers that are uniformly applicable across the whole nation. With the wide range of weather it is simply destined to fail....See Moremacv
14 years agochipster_2007
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