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Water Vapor

Posted by Harold Kestenholz on August 2nd, 2000 04:58 PM
In reply to see my other reply for comments... by jb on August 2nd, 2000 03:16 PM [Go to top of thread]

The information you are missing relates to water vapor. You are correct that uncracked concrete can stop leaks of liquid state water, it is used for pools. The problem with humidity settling out on cold surfaces (dew point) is that humidity is the result of water vapor (the gas state of water) passing through a porous solid (like concrete). It is water vapor that can pass through seemingly "solid" material to settle out on surfaces, forming larger and larger drops as in the process of creating rain and hail. Air and the moisture in it are a mysterious, invisible concept to many.

The references given recommended placing plastic sheet on both sides of the insulation that would be up against the basement wall. The idea is to prevent any moisture from getting into the fiberglass from either side. That is - sealing the fiberglass.

In this case, there are a lot of unknowns: Is the basement wall sealed outside or at the inside surface. How cold will the wall get? The prudent advice is to permit moisture to leave the insulation through circulation even after it may have collected for some time in the winter. The holes left by staples through the plastic may not be enough.

If the present installation does not have wet fiberglass next to the basemant wall now. What harm will Tyvek do? IMHO prudent advice is to allow the moisture to leave, as it does now.

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