I am working, doing audits, with a contractor who tends to make basements, crawlspaces into conditioned space. Especially when all or most of the duct work is in the crawlspace. He does this by covering the floor, side walls and piers with heavy plastic. He then uses rigid foam insulation on the walls, foams the joints and above and seals the vents and access hatches. Then we duct seal and re-insulate.
Has anyone been doing this for a while? Any unentended consquences?
Be sure plastic is protected from mechanical damage by any future workers or residents accessing crawl space
Be sure to leave exposed strip for termite inspection. If termite bond is in place, be sure they are on board with details of the project - termites can tunnel, unnoticed through foam.
The above may sound as if I don't favor sealing crawl spaces, but in fact I do.