We have a 2-story addition over pier-and-beam that we have just built attached to an existing 1-story slab foundation home.

We’re nearing completion (foundation, framing, roof, drywall, rough electric and plumbing are all in) and I recently started asking about the crawl space (I’m the owner, I have an architect, engineer, and contractor on the job).

As far as I understand it, there’s going to be a concrete skirt with vents, a loose-laid moisture retarder on the ground, a continuous layer of Tyvek under the beams, batts between the beams, and then the wood subfloor with taped seams, leveling quick-set if any needed, silicone paper, cork flooring.

Some additional facts:
* We’re in Austin, Texas
* The expansion is over a flood zone (500 year per FEMA, 100 year per city)
* FFE is between 2-4 foot above grade depending on where you are measuring and at all points at least 3 feet over the floodplain
* Because this is over a flood zone we cannot fully encapsulate (we need leave inlets and outlets for floodwater)
* We’ve lived in this home for 15 years and during the worst flood the water was still about a foot in height and 8 feet and distance away from where, but 100-year floods happen sometimes

So what should we do to prevent this from turning into a mold factory?  Continuous sheath polyiso under the beams?

Thanks in advance!