I just had a presentation from Smart Energy Today. They told us reflective sheets in a crawl space will improve home efficiency. I got a link to your web site from DOE. I have already determined I need to seal the crawl space ducts. After that, does the reflective sheet stapled to the floor joists make sense? I live in Pacific Northwest. West of the Cascade Mtns.
Using a reflective insulation or radiant barrier in a crawl space will reduce heat lose through the floor. How much that will save in energy costs is hard to quantify and might not be enough to justify the cost of material and installation. However, the major benefit to you in your climate would be to mitigate the effect of moisture transmission from the crawl space into the floor, and that could be very important. You can contact any RIMA member who has their products listed on the Verified Products page on the RIMA web site for costs of the material you might need. A local handyman can easily make the installation.