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I have a vapor barrier in my crawlspace which is made of multiple sheets of 6-mil plastic.

One contractor suggested that in the dry months I should pull back the sheets of plastic and allow the dirt beneath to breathe and dry out.

A second contractor said that the first contractor was repeating an urban legend, and that I should not pull back the vapor barrier.

Should I periodically pull back the vapor barrier in my crawlspace?

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up vote 12 down vote accepted

"allow the dirt to breathe" doesn't even sound like an urban legend. Just sounds plain pointless. The entire point of the vapor barrier is to keep the moisture out of the crawlspace--so leave the barrier there. The dirt will be OK.

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The vapor barrier is there to keep the moisture in the ground and the humidity in the crawlspace down below the level where mold grows and wood rots. It is left permanently in place to achieve this goal.

Under house humidity control consists of several systems.

  1. A vapor barrier to stop soil surface evaporation from driving moisture into an enclosed space.
  2. Crawlspace ventilation with the appropriate number and size of screened vents to carry off moist air from any left over evaporation that might take place.
  3. In the case of excessive soil dampness, a perimeter drain to help lower the water table under the house. It's purpose is not only to reduce the amount of moisture in the soil but also to prevent standing water under the house in wet weather.

Basements open up a whole 'nuther can of worms.

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