Share 'Closed cell foam on underside of my hardwood floor?'

I have white oak hardwood floors on an old 1920s house. My contractor is offering to do 2" of closed cell foam on the underside of my hardwood after he does the attic roof. I have no other sub-floor other than these tongue/groove hardwoods, so closed cell would be applied directly to it.   It is pier and beam house with about 3 feet of crawl space - in Austin TX. Is this safe?   Or is it dumb? Po…