Arm yourself with a headlamp or flashlight and a screwdriver. Say good-bye to the family and crawl under the house. There should be. Plastic provides an excellent vapor barrier which helps prevent decomposition of joists and other support structures. Newer houses should have sill plates of pressure-treated wood.
Examine floor supports for rot and insect damage.
Tap on suspect wood with the screwdriver to test how solid it sounds. Note its location and brush it away so you can tell next time if damage from carpenter ants is still occurring. Remove any rodent nests, a source of mite, flea, lice, bed bug and tick infestations. When you have crawled back to the outside world, write a brief report to use for comparison next year. You are not quite done yet.