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water barrier

Posted by Harold Kestenholz - Hydronic Network on August 2nd, 2000 02:26 PM
In reply to ditto to jb by bc on August 2nd, 2000 10:40 AM [Go to top of thread]

Water is my game. The idea is to know where the water is coming from - and then to keep it from collecting. The moisture in a basement comes from the ground. A different effect results in winter and in summer. A basement wall is not all one temperature. In the winter, the top part is as cold as the outdoors, the bottom is 50 or so.

Moisture as a vapor (humidity) passing through concrete (it is porous, unless sealed) will collect on the cold surfaces, so you are partially correct about the moisture passing from inside the room to the cold basement wall, and collecting there - but moisture will also leave the bottom of the unsealed wall to collect at the cold spot. The question is - do you want to trap it there, or permit it to leave the colder spot to expand to create a lower relative humidity in the basement and rooms of the house. The relative humidity in the house in the winter will be about 35%. And moisture will leave one area to pass to another.

There are several considerations here: Is the house in Florida or in a northern climate? Is the basement wall already sealed outside?- then sealing the insulation with plastic will not hurt. Is the basement wall unsealed outside? - then moisture WILL pass through and collect on cold surfaces (dew point.)

Tyvek wrap IS placed on the OUTSIDE of the house to let moisture in the wall pass through and not collect in a cold impermeable sheet of plastic. It can do the same job in another place.

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