Is this house on piers? Is there sufficient air movement below the house? We once worked on a 200 year old home where the new owner bricked up the perimeter of the house to keep critters away. This had the unintended effect of trapping all the moisture below the house. The beams were dripping wet. When she removed the perimeter brick skirting, the house dried out.

It's wide open on all sides. It was fine before when the moisture could escape in both directions. As sson as I put the vinyl floor down, it created a trap between it and the hardwood. Only about an 800 square foot house. About 1.5' of the ground.

Have you insulated walls and attic ? The 'chimney effect' will draw in more moisture than a house that doesn't let in as much air. We insulated the underside of our pier and beam house, then, after all the electrical work was complete, stapled Tyvek under the joists. Do put the wording facing the dirt. Tyvek is meant to breathe a little.

Walls and attic are insulated. Im thinking that whatever I do for insulation, it will be a moisture barrier as well. So if thats the case, I should not put a barrier on the new subfloor? Right? The original subfloor had tar paper laid between it and the hardwood. I'm thinking if I put that back down and put insualtion under the house, I'll end up with a trap for moisture to stay in between the to barriers.

The thought on moisture barriers; place the barrier on the side of the assembly where the temps are the warmest and most humid. For us southerners, that's right below the leaky siding on the exterior walls. We don't use a vapor barrier on the inside of a standard wall as the HVAC system takes care of anything that gets past the barrier. The insulation needs to breathe. You don't want the dreaded moisture sammich. Think of this as a wall laid flat.

So no barrier on subfloor? Just one on the insualtion?

Edit: Vapor barriers need to be installed on the warm side of the insulation, in this case the outside. Thanks ionized.

No moisture barrier is needed if using spray foam.

That makes sense. Talked to a spray foam company yesterday and they confirmed there is no need for a moisture barrier when going with a spray foam.

thanks everyone

Vith, that is entirely wrong-headed in a hot, humid location. The floor assembly needs to dry to the inside because is certainly not going to dry to the outside.

Ah, you are correct ionized, thank you. I am used to vapor barriers in a cold climate which are installed on the inside. Vapor barriers need to be installed on the warm side of the insulation, in this case the outside.

all you need to know & more. best guide to insulating floors

of raised houses to date. and specifically for hot humid climate.

https://www.lsuagcenter.com/NR/rdonlyres/D33F711D-DC4B-4E4C-9ED6-A97DCE9DB026/79805/pub3187insulatingraisedfloorsLOWRES.pdf