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Harold is all wet... Tyvek and Vapor barrier 101

Posted by jb on August 2nd, 2000 10:23 AM
In reply to Plastic vapor barrier by Harold Kestenholz - Hydronic Network on August 1st, 2000 04:06 PM [Go to top of thread]

Hi Harold, I like some of your other posts but I think you are WAY off on this one. The plastic sheeting as described in the question should act as a standard vapor barrier and sounds perfectly appropriate in this application. I would only hesitate if there was any pre-existing water problems where the water was leaking in to the basement from the outside. In this case you wouldn't want to trap this water behind the insulation.

Tyvek is a wind barrier, air infiltration blocker that is used on the OUTSIDE of houses. Its purpose is to stop drafts from entering your house. It has extremely small perforations, similar to gortex, that allow water vapor to pass through but blocks wind and most liquid water. The reason that it is used instead of felt paper on the OUTSIDE of buildings nowadays is so that you don't get either a double vapor barrier or a vapor barrier on the outside of your insulation. Either of these circumstances can cause condensation in the wrong place and rot away your house.
Plastic sheeting is used as a vapor barrier inside the insulation. If the air inside your house is 70 degrees then it ends up holding more moisture than the air outside that might be 50 degrees. This moisture, or water VAPOR, if not stopped by a vapor barrier will go through the insulation and condense on the cold exterior plywood, or in this case - cold concrete basement wall, causing a moisture problem. Plasic sheeting stops condensation BECAUSE vapor doesn't pass through it. There won't be any condensation if the plastic PREVENTS the vapor from reaching cold surfaces.

In the case of this basement, Plastic should help any moisture situation in that it will reduce any condensation and probably lessen the need for dehimidification that is required in most basements. Tyvek will neither help nor hinder any moisture situation. It will protect the young ones perhaps as well as heavy mil plastic but it probably costs more than 10 times as much. This expense is not needed.

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