Housewrap (tyvek etc)
[This message has been edited by LDoyle (edited December 13, 2002).]
Water gets behind brick, vinyl and stucco. It does, that is fact.
The idea is that you are protecting the sheathing from water, not water vapor. The wrap cuts wind but does not stop air. It is like Gore Tex is the clothing industry.
There is no wrapping school. It is a product that has put out there for contractors to use. No one has told them how to use it properly. Now whether it is used correctly is another is OUR problem. I see it misapplied constantly around here.
If you apply it so water get behind it, then you are going to have moisture problems. There are many ways to misapply this product, like any product.
Home building codes have attempted to improve energy efficiency without looking at the effects these changes make. Moisture problems are one of these problems.
Try building science .com for usefull info on home construction practices
Mold requires moisture and darkness to grow.
Housewrap does not contribute in any way to increasing moisture or darkness in a home.
As already mentioned, housewrap is an air barrier but it allows the free flow of water vapor to pass thru.
Behind all sidings you need a secondary weather barrier. The purpose of a secondary weather barrier is to prevent wind and sun borne moisture from pentetrating the siding and damaging the sheathing.
Housewrap is but one such secondary weather barrier and in fact #15 or 30 lb roof felt performs better in most circumstances. Foam boards can also be used as secondary weather barriers.