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Closed cell spray foam over old mudsill

WildBunchFarm | Posted in General Questions on


I have a 1920s duplex that has a large old growth mudsill.  The inspection report said that a few parts of the mudsill had some moisture damage.  The reason for this moisture damage is probably because of the excessive moisture in the crawlspace.  Currently, the crawlspace is vented without any vapor barrier.  There are no downspouts that bend away from foundation and in fact, some portion of gutters are missing.  

I have a contractor who wants to turn the crawlspace into a conditioned crawlspace.  He wants to run 10 mil vapor barrier up the brick foundation up until the bottom of the mudsill.  He then wants to use closed cell spray foam on the walls and on the mudsill, leaving a one inch inspection gap on the mudsill.  However, most of the 8 x 8 mudsill will be covered on the interior with spray foam.  

Is this a good method?  Or should I go with foam board insulation and leave the mudsill exposed.  

Thanks for any good advice.

Jimmy Nguyen

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Jimmy,

    Conditioned crawlspaces are considered best practice in many areas, though there could be some other concerns with your mudsill. It is important to make sure it is not getting wet from the outside, from rain, and if it is to fix that first. It would also be a good idea to see if there is a capillary break between the foundation wall and the mudsill. And It would be helpful for GBA members to know where your house is located to advise you on this. In the meantime, this article may answer a lot of your questions: Building an Unvented Crawlspace

  2. WildBunchFarm | | #2

    Thanks, Brian. The house is in Richmond, VA. There is no capillary break between brick foundation and mudsill.

    Does anyone have reservations about using spray foam over the mudsill?

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