Your basement or crawlspace is usually the coolest spot in the house because of the insulating effect of the ground. That means that warm, moist air coming inside condenses on surfaces, including your pipes, causing dripping or sweating. Besides being annoying, dripping raises the humidity level in the house and increases the chances for mold growth. To reduce this problem, make sure all vents to the outside are closed, and add foam pipe insulation to the parts of the pipes you can reach.
