In flood-prone areas, elevating the floor system of a building above the anticipated flood level can significantly limit the extent of property damage associated with flooding. In hot and humid climates, such as the Gulf Coast region, homes have long been constructed with raised floors on crawl space foundations. Recent changes to building energy codes require floors to be insulated. The majority of residential buildings in the Gulf Region are now air-conditioned. The combination of floor insulation and air-conditioning, however, may put floor systems at risk for summertime moisture accumulation and related problems such as mold growth, decay, corrosion, and expansion/contraction damage. In response to a research gap and regional need, researchers from the Forest Products Laboratory, in cooperation with Louisiana State University Agricultural Center, monitored moisture and temperature levels in a dozen homes in New Orleans and Baton Rouge, Louisiana. This research confirmed several trends that were expected, relating to the effects of summer air-conditioning temperatures and impermeable interior floor finishes. It was found that foil-faced rigid foam board and closed-cell sprayed polyurethane foam insulation performed well, keeping subfloors from accumulating moisture. This work provides a research basis for builders, contractors, homeowners, architects, and building officials to make informed decisions.