Roof rats are smaller than the Norway rat and have a tail longer than their body. They live in the upper portions of buildings and trees and are excellent climbers. Again, rats can enter through a half-inch gap and chew small holes into larger ones to gain entrance. They are nocturnal, shy and cautions about changes in their environment. Rats can cause significant structural damage by chewing wood framing in buildings and homes. Many structural fires are caused by rodents chewing the electrical and computer wiring. Rats are associated with various diseases and occasionally bite.