vaulted ceiling & wall insulation

Old 02-07-04, 12:14 PM
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vaulted ceiling & wall insulation

I am putting an addition on my home and I've been told to use R-38 in the ceiling, and R-19 in the walls. I put kraft-faced in the ceiling and installed a vapor barrier. After talking to a local inspector, I was told to remove the vapor barrier and either replace the batts with unfaced insulation or basically shred the kraft face with a utility knife and put the barrier back up.
Also, in the walls I put in an encapsulated batt (johns-mansville comfort therm) and was told again to shred the face then poly over, or replace with unfaced. I was told this encapsulated product should not even be sold, as it violates local building codes. The inspector said that the vapor barrier would be too much, and I would have moisture problems. HELP!!!

Last edited by ME262; 02-07-04 at 04:51 PM.
Old 02-08-04, 05:41 AM
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There should be only one vapor barrier. If a second is there, slit the barrier to allow free movement of moisture. Or remove the extra barrier, if possible. Shredding is not needed.

According to Johns Manville, the poly wrap on its insulation serves as a vapor barrier. Therefore, you would not want any added vapor barrier with it.

Whether or not something satisfies the local building code is a matter for the framers of the local building code. You probably cannot win an argument with the local inspector; only when his requirements are met by facts could this be settled amicably.

Here is some added information on vapor barriers for your consideration.

Hope this helps.
Old 02-08-04, 08:19 AM
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chifite is quite correct, you are not going to win an argument with a building inspector and the site chifite has provided is quite informative about moisture control concerning "Thermal-Moisture Dynamic". On this site you want to read "Perm Ratings". This is what Manville bases their product on. And if you contact them, they will state the same or a similar principle. Since you worked with this product you would have noticed that one side of the plastic encapsulation has a much thicker plastic than the other three sides of the encapsulation. It is this side that faces the warm side of the structure and has the flanges on its side. Whether or not this is acceptable to local building codes is clearly up to them.

The term "Perm" in Perm Rating stands for PERMABILITY and since all materials used in the construction of a house have a Perm Rating, not only vapor barriers, it explicitly implies that the water vapor molecule will traverse every material in the house. On top of that, it works both ways. For example, all heat has moisture in it. During the winter the heat flow is from within the house towards the outside. In the summer, the heat flow is from outside the house towards the inside the house. The difference between the two heat flows is that the heat is confined within the structure during the winter and the heat outside during the summer is not confined. It is for this reason why vapor barriers are installed on the warm side of walls in areas where they experience more than 2,200 Heating Degree Days (HDD) a year.

As your heating system heats the air within the house during the winter, that air expands but the house cannot get bigger. This creates pressure with in the structure, which accellerates diffusion. Diffusion applies to both heat and moisture as it traverses a material. Insulation retards or slows down heat flow (Diffusion) but not moisture flow. Vapor barriers slows down or retards moisture flow but not heat flow. In reality what vapor barriers do in conjunction with insulation is create balance, which is the best term to describe nature. What justiifies the application of the vapor barrier to the inside is the pressure produced from heating air within the structure in cold climate areas. This applies to the entire structure, including basements. There is a site someone has posted from a "Building Science" organization about insulating basements and not applying vapor barriers. This site clearly omits heating of the basement, for if it did all its support would be reversed, diffusion, capilliary action and sources of moisture. What is unfortunate here is that most people who insulate their basements, usually heat them too. I must state that I deeply respect and admire the work the people have done in this organization, however, this does not mean I agree with them and the site does not imply that heating does take place in the basement.

The logic of the building inspector is based on the aforementioned, but it goes a step further. This has to do with Perm Ratings of materials and the ability of materials, including air, to absorb and expel moisture. Its whole purpose is based on balance, where the amount of moisture introduced to a material or air does not exceed its ability to absorb and expel the humidity. For if it does exceed, an inbalance occurs and condensation is highly probable. Hence the rule 5 to 1 when applying materials after the vapor barrier. Attic are vulnerable to this than walls because all roofing materials have very low Perm Ratings. Hence the need for attic ventilation and not wall ventilatiion. Attic ventilation bypasses the low permability of the roofing material.

Whether or not I agree with your local building inspector, is of no consequence. For in the end they have the final say and their rules are based on sound principles.

Last edited by resercon; 02-08-04 at 04:25 PM.
Old 02-08-04, 07:42 PM
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Thanks for your knowledge and honesty. I'll give it a go. Wish me luck!

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