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Tyvek info...

Posted by jb on September 6th, 2000 01:19 PM
In reply to tyvek failure? by Chris Dawson on September 6th, 2000 10:30 AM [Go to top of thread]

I have never heard of any problems. Unless we are all being duped, the concept is that water and wind are kept out and water vapor is let out. This is sort of how gortex in rain coats and jackets work. There are small holes in the material that are small enough to stop wind and water as a liquid but large enough to allow the smaller water vapor pass through. In a house this ends up reducing the amount of moisture that comes into contact with the sheathing and reduces the occurance of rot and mildew. To be effective it must be installed correctly. I think if there had been any major defects in this material or concept I (we) would have heard about it, so I am deciding it is ok by inference. You really can't think about Tyvek alone, apart from all of the other elements that make up a modern sidewall system (for want of another term). Its use becomes more critical the tighter a house becomes. It complements the proper use of an interior vapor barrier and is a waste of money if applied in addition to tar paper. It is merely one element in a whole house concept to manage the air, moisture and insulation etc. in a modern house and its "envelope".

From (
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. Siding, whether it’s vinyl, wood, stucco, brick, or composite, does not completely prevent air and water penetration. Tyvek® is designed as a secondary defense to help manage a home’s wall systems.

Moisture Vapor Transmission Rate or perm rate of a material determines the ability for water vapor to diffuse or evaporate through the wall. The higher the perm rate, the more "breathable" the material is and the easier it is for water vapor to pass through. Materials with Perms below 1 are considered vapor retarders since the rate of moisture vapor flow through a 1 Perm material is so low there is essentially no flow. Tyvek® has a Perm rate of at least 58 Perms which is very open to allow moisture vapor to flow through.

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