Insulation codes are based upon the climatic factors of the area for which they are written. A warmer climate has a code that requires less insulation than a colder climate. The local climatic zone can be determined by using a climatic zone map and the corresponding chart available at web.ornl.gov.
Insulation is rated based on R Value. The higher the R value, the more energy efficient a building is. Many builders try to exceed minimum insulation codes because it cuts down on heating and cooling costs over time. The insulation required for roofs and walls is different. For example, the local building code might say that a roof must have R-30 insulation whereas walls can have a minimum of R-13.