But if books or clothes are placed in cardboard cartons and then put on a wet basement floor, they often are ruined by mildew. You may want to attempt to seal the walls and floor against moisture with special paint. And you could air it out, possibly using fans and dehumidifiers. If you do use the basement for storage of things that need to be kept dry, consider keeping them off the floor by hanging them on hooks inserted in pegboard or on racks mounted along the wall. If some items are placed on the floor, it might be wise to put them on sheets of plywood or plastic.

Why be concerned? Consider just one of moisture’s “children”​—mildew. Mildew is fungi that appear as a gray or white fuzzy mold. It can be found on anything, but is particularly destructive to books. A small-wattage light left burning in closets will deter it. Airing out possessions and letting air circulate in the closet will also help.