I’m having a bathroom installed in a sunroom conversion to 4 season room. Due to the layout of the room we were hoping to only install infloor heating to the bathroom portion as it won’t get much heat off the rad system that exists on the main floor.

The entire room itself is over a non vented crawl space. I know I can either insulate the walls or the ceiling in the crawlspace. Using rigid xps foam what would be better to ensure moisture isn’t built up as well as preventing pipes from not freezing in the winter? I get both hot humid summers and cold winters in Southern Ontario, Canada.

Also, will there be any issue overlapping xps on interior joist spaces with exterior foam running under the siding down just below the concrete foundation?