Added on a new family room has a crawl space only 3 ft from ground . I insulated in between the floor joist and screwed 2″ foam to the bottom of joist . And ran the duck threw the floor joist as well. It sit on a beam so the ground is dirt and I want to close this in can i or should I cover the ground with plastic. Then what should I use for the outer walls concerned about mold and don’t want the wood sitting in the dirt .
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No reason not to put plastic on the ground, regardless of what you do with the walls (and provided the crawl does not get water running into it.
If your 2" foam is reasonably
If your 2" foam is reasonably tight-fitting at its joints, you will have an excellent vapor barrier to isolate the floor system from any moisture originating from the dirt below. Covering the dirt with plastic sheeting would be extra insurance againt moisture that could affect any framing not covered by foam board.
The concrete stem walls could be a path for wicking moisture from the surrounding outside ground, depending on local conditions and on how well you direct rainwater away from the foundation. Even then, if the outside of the concrete was thoroughly sealed with tar, there would be very little moisture migrating thru it into the crawl space..
You need to ventilate the crawl by some method, and your options on that can be explained by your local jurisdiction/building inspector.