Average outdoor dew points in Nashville are such that it's better to use a sealed-insulated crawlspace approach and ventilate it with conditioned space air rather than venting to the outdoors.
A 10-mil poly vapor retarder on the floor mastic-sealed to the stem wall with 2-3" of rigid EPS insulation held to the walls with furring through-screwed into the foundation works. Sealing & insulate the rim joist and foundation sill to the foam. If termites are a problem in your area use thin metal flashing at the top of the foundation over the rigid foam to block potential tunneling paths through the foam to the susceptible wood, otherwise you'd need to leave a 2-3" gap in the foam for inspection purposes. A couple of floor grates/grills on the first floor at opposite ends of the crawl may be all that's necessary, but monitor the humidity. If it stays above 60% RH it may be necessary to install a room-type dehumidifier (drained to a sump, or a condensate pump for convenience) to manage the mold risk. Subsoil temps in Nashville are high enough that simply by thermally earth-coupling the crawlspace with wall insulation and controlling humidity in the conditioned space to below 55% would likely make a crawlspace dehumidifier unnecessary.
Unless you're positive that there is a good moisture proof sill gasket between the foundation sill and concrete/masonry, use only UNfaced rigid insulation, since the foundation still needs to dry through the foam into the crawl sometimes, lest the moisture be forced higher, endangering the foundation sill. With EPS you can go as thick as 4-5" , but with XPS it's better to hold the line at 2". Don't use iso unless you're positive it never floods. And don't use air-permeable fiber (batts, or blown) in a mini-studwall or you'll likely create rot conditions at the exterior edge of the studs.
|