Think about what's in the room above your heirlooms, too.
Heat causes damage.
Don't hang valuable objects over radiators, heat-producing appliances or the fireplace. Books you want to read twenty years from now shouldn't be shelved on the mantel, the window sill or the radiator. Light causes fading and other damage. Don't put valuable books and papers where they'll get direct sun or bright light of any kind. Hallways or other rooms without windows are best.