Share 'Treating crawl spaces (with ductwork) when the adjacent basement ceiling is insulated.'

I am currently speaking with a homeowner who would like to replace the existing FG batt insulation in the ceiling above his crawl space. The crawl is connected to the basement, and the basement ceiling is insulated with FG batts as well. The crawl has ducts insulated to R-4.2 throughout it. The crawl floor is a thin layer of concrete (about 1"). I spoke to him of two options: 1. Slap R-19 un-fac…