Barn insulation

[DVerbarg]

Shade2u2,

To your question: <font color=blue>Is the Tyvek house wrap perferated to allow breathing? </font color=blue> Tyvek's web site states:

<font color=blue>The unique, nonwoven-fiber structure of Tyvek® HomeWrap® resists air infiltration and water intrusion, yet is engineered to readily allow moisture vapor to diffuse through the sheet, helping prevent mold and mildew buildup and wood rot. The fibrous structure is engineered with microscopic pores that readily allow moisture vapor to evaporate but are so small that bulk water and air cannot penetrate.</font color=blue>

Regarding if it is ok to use with plastic type vapor barrier on the outside that would depend on your geographic location and construction techniques. I've seen houses that have no problems and others that have had severe moisture damage in the stud spaces due to trapped moisture. The problems have been the exception and are probably due to poor construction techniques that allowed water, not just moisture, into the wall cavity (which is more "moisture" then the Tyvek can quickly allow to dissipate).

 

[beenthere]

The answer is yes to both questions.

 

[StoneHeartFarm]

Shade2u2

The others have it right. Yes you can use Tyvek with a vapor barrier, in fact it's part of the same system. Think of a wall this way: drywall, vapor barrier, insulation, sheating, housewrap, foam, siding.

The purpose of the vapor barrier is to keep inside moisture from getting into the wall. The purpose of the house wrap is to keep Outside moisture from getting into the wall and allow any moisture that DOES get into the wall to breathe through the housewrap and get away from the sheating. The foam keeps that moisture from freezing in the winter so that it doesn't freeze on the sheating and wait till spring to all thaw at once. Ideally, any moisture that does get into the wall will move through the insulation, sheating and housewrap and run harmlessly down the inside of the foam. A good vapor barrier keeps this to a minimum. The paper backing n insulation is not considered a good vapor barrier. Just don't over do it, I've seen a very few homes that have been way too plastic lined and the homeowners have had moisture problems. If you use a vapor barrier, a ventless LP heater may be a bad idea for instance because they emit a heck of a lot of vapor that has to go somewhere.

I used Pink wrap rather than the Tyvek. Pink wrap is a woven product, which makes it easy to imagine moisture passing through the tiny cracks. Maybe somebody that has experience with Tyvek can answer this, but I don't believe it is woven the same way as pink wrap.

SHF

 

[BHarrison]

The cost of spray foam will far outweigh anything else. It runs about 2x more than any other way of insulating. They payback is in utilities usage. I have a standard construction home that I had faom sprayed in the walls, and you would be suprised how little my A/C unit (Geothermal Heat-Pump) runs.

I too am confused about how that guy was figuring a square foot, but when they quote, they should know if they're quoting a stud wall or a metal building. What is sprayed on a metal building is a totally different mixture than what is sprayed in a stud wall. They are different densities. What is sprayed in a metal building is much more dense, and only expands to apx 1 1/2". What goes in a stud wall is more "soft" and will expand to about 6". (They shave off the excess) All of this comes from about 1/8" of product sprayed on the wall. One nice factor is that it is dense enough to screw into, but there is also a difference in fire ratings. The denser material will burn easier than the lighter material.
As far as pricing goes, I had my house done in 2000 and it was around $4.75 / sf. (1x1) They quoted me about $1.75 / sf for my shop.
I hope that made sense. I'm not very good at explaining things.