High humidity is as hard on your house as it is on you and your family. Extra moisture in the air can make your floors swell, your furniture finishes turn cloudy and your walls crack. The moisture may crack the drywall, but it more commonly causes the water-soluble joint compound covering the taped seams to deteriorate and form hairline fissures. You can easily repair cracks with joint compound, but you should heed a warning. Cracks in the wall can have a more serious cause -- foundation settling. If that's the case, cosmetic repairs may not be enough.
Run a 4-inch drywall knife over the crack to scrape off flaking paint and old mud. If any paper tape has separated from the wall, cut it off with a utility knife and scrape around the area to remove loosened mud.
Fill cracks wider than 1/4 inch with patching compound, which is a wall repair material that sets to a rock-hard consistency. Mix a little of the patching compound powder with water to form a stiff paste and trowel it into the crack with a putty knife. Scrape off all the excess. Patching compound is difficult to sand once it sets.
Apply fresh drywall tape to any areas from which you removed peeling tape. Spread joint compound on the area and lay moistened tape in the fresh compound. Scrape over the tape with the drywall knife to flatten it.
Cover the repair with a coat of drywall joint compound and scrape it flat. Let it dry overnight, then apply a second coat. Sand the final coat with 120-grit sandpaper when it dries.
Coat the repair with drywall primer. Let it dry, then apply a coat of paint to complete the repair.