Raised floor over pool/vented crawl, Warmboard + Spray foam – GreenBuildingAdvisor

Hi all, 

I’ve lurked on GBA for a while but this is my first time posing a question.

I’m working with a client to convert an indoor pool room into a great room, and part of that scope is to build a new wood floor with warmboard radiant panels over the existing pool/patio. Old house in Climate Zone 4A.

My initial preference was to demo the pool/patio and put down a new slab with insulation and vapor barrier, but  that would have been too easy. I won’t go into much more detail about why it isnt being done that way, but I will tell you that the pool has been dry/unused for multiple decades, the pool and patio around it/the entire room is solid concrete with a wet-laid brick finish floor.

Access to the underside of the raised floor will be impossible, so insulation will be installed from above. Typically we like to make our floors over crawl spaces fairly tight (spray foam) but I’m concerned about potential moisture issues in the cavity between the spray foam and the warmboard.

My question is this: Is warmboard considered a vapor retarder/barrier due to the aluminum skin, and should I be concerned about potentially trapping moisture in the cavity?

The proposed floor assembly is as follows:

-TOP-

-Eng wood floor finish on top

-Warmboard-R

-3/4 T&G subfloor

–SPRAY FOAM -OR- MINERAL WOOL BATTS (see below)

-TJIs with plywood between, nailed/screwed to the bottom “flange” to make insulating the floor easier.

-build new raised wood floor over top, with ~1.5-2″ air gap to the brick below

-keep existing pool and brick patio as is

-BOTTOM-

Though the space under the floor is small, I am considering this a crawl space. Particularly with the existing pool volume that exists under much of the floor. New vents will be cut into the exterior wall, trenched/cut to the pool volume to treat this as a vented crawl space and to ensure the space under the floor has as much drying potential as possible.

Contractor is adamant about spray foam in the floor cavity, however I am concerned about potentially trapping moisture in the cavity between the warmboard on top, and the spray foam below.

I do not know if the aluminum skin on the warmboard constitutes a vapor retarder/barrier, but my gut tells me to keep the bottom of the assembly vapor open with a mineral wool batt in the cavity. This would at least ensure that drying is possible down to the crawl space below.

If warmboard turns out to be vapor open, all i’ve done is allowed vapor to possibly move in two directions. 

Am I overthinking it?

I need some outside feedback, because this is all going around in my head in a loop.

Help.