Why does the house creak at night?

	Art by Mike Dammer.

As the outside temperature goes down, the wooden boards and metal parts that make up the house contract a little. The metal parts contract more than the wood does, so the nails, pipes, air ducts, and so on rub against the wood. Also, wood rubs against wood. All that rubbing can make creaking sounds. At night, when the whole house is cooling down and everyone is quiet, we may hear a lot of creaking.