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Semi-conditioned New Build Crawlspace

Andy222 | Posted in General Questions on

I recently moved into a new construction single family home on a crawlspace in upstate SC. The builder put in a loose vapor barrier, sealed the vents with foam, and installed a dehumidifier. While it may be “sealed” there is still plenty of places for air to get in either through the door or between the foundation and wood framing. I recently started tracking the humidity and it hovers around 65% depending on the day and the dehumidifier is always running. My question is do I need to have this space resealed to lower the humidity or is 65% OK? Most of what I have read says 50-55%.

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  1. user-5946022 | | #1

    A sealed conditioned crawl needs the dirt floor sealed off. You state there is a loose vapor barrier. What are the crawl space walls made of?
    Typically, in a sealed conditioned crawl, there is an very heavy duty and thick vapor barrier material that runs partially up both the perimeter wall any structural piers in the crawl, and is sealed to the wall and piers to prevent air movement from the soil into the crawl space. The separate pieces of the vapor barrier sheet are sealed to each other with tape made specifically for that. Any penetrations either from things coming up from the ground (water pipe, sanitary line) and penetrating the vapor barrier are also sealed tight. Often the material used for sealing the vapor barrier to the wall and piers is closed cell foam.

    If your vapor barrier is not sealed, you don't have a sealed crawl.

    Before you seal the vapor barrier or get someone else to do it, I STRONGLY suggest you take up the loose vapor barrier a section at a time and rake any stones or other sharp objects out of the dirt.

    Yes, the door between the sealed crawl and the exterior also needs to be sealed. What type of door is it?

    You are correct that the space between the top of the foundation and the sill plate should be sealed, and there is often significant leakage at that point as well. How you deal with it depends on where you are - if it is an area susceptible to termites the options are more limited than areas where that is not a concern.

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