The following links provide the latest building energy code requirements:

Building Codes Assistance Project - BCAP
BCAP provides free assistance to states and municipalities in their efforts to adopt and implement both commercial and residential energy codes.

2009 International Energy Conservation Code (IECC)
This Department of Energy website offers the latest insulation requirements under the 2009 building energy code (called IECC).

U.S. Department of Energy - Status of State Energy Codes
View a state's building energy codes.