What the others have said ultimately. Ventilated crawlspaces likely account for 95%+ of construction in the area, as that was the prevailing wisdom of "how to build" prior to recent years. Most old/ pre ~1920 homes in the region were built on short piers, w/ no vapor barrier at all, w/ no sidewalls and that actually worked much better that partially ventilated crawls, as there was continuous air-flow to keep things dry. Partially ventilated crawlspaces, especially in the SE due to our extremely high summer ambient humidity are inherently problematic as the airflow is severely limited by the placement of the vents, which is often too little, creating pockets of dead air that just collect humidity/ invite wood destroying insects, etc. Anything over 70% humidity is no good from that respect.
As an aside, basements tend to be more popular in the North due to the deeper frost line/ foundation depth requirements there. If you're digging down 4' to get below the frost-line, it's somewhat of a no-brainer to just go a few more feet and get the usable space. Here in the SE, our frost line is only 12", so the economy changes a bit there.
Modern construction/ building science points clearly to a sealed encapsulated crawlspace as being the best bet here. ESPECIALLY, (and as a structural engineer, I would say required), if your floor system uses engineered lumber, (TJI, etc). I've seen 10 year old homes absolutely ruined w/ rotten TJI framing members constructed over a poorly ventilated crawlspace w/ a cheap vapor barrier). No cheap fix at that point.
I will also admit the cost to have it professionally retrofitted is high - quite frankly, because it can be. Its not that the work is inherently difficult or requires expensive material, it's just damp, dirty, crawling around on your knees and stomach work. No fun whatsoever, but if you're physically able, you can easily save thousands doing it yourself.
IF you have a vented crawlspace, and traditional/ dimensional lumber joists that appear in good shape, no mo**, mildew, insect damage, etc, the best compromise to a fully encapsulated crawlspace would be a 100% vapor barrier, close your vents, (summer and winter), and put a few box fans/ air movers underneath, (NOT the fans that are marketed to replace your foundation vents, and that sucks in air from the outside - our air is to humid in the summer, and those will create a real problem) strategically aimed to keep air moving in the crawlspace/ keep things dry. I once had a handyman/ friend that I would hire for a day here/ there to help me with "2-man" projects, just as a second set of hands ultimately. He smoked, and while I dont, and would certainly never allow smoke in the house, I'd let him smoke in the crawlspace when I was tacking this in a previous house we owned years ago. If there was enough air movement to move the smoke away, all good - if the smoke just sat there, I'd move the fans around/ aim a fan into that area to keep air movement everywhere. It was a good way to find dead spots of air for sure, but I'm sure a smoke stick, incense, etc would accomplish the same thing.
Welcome to the South!
