In warm climates where high humidity conditions occur on a regular basis, vapor retarders should not be installed on the interior side of the building. In these warm humid climates, it is permissible, but not required, to install batts with the vapor retarder on the exterior side of the building. Warm and moist climate areas, such as the Gulf Coast and Southern portions of the U.S. Atlantic coast, are shown in the climate zone maps in the International Energy Conservation Code and ASHRAE 90.1 Standard. In warm climates where high humidity is not a factor, such as the Southwest U.S., vapor retarders are not required, but if a vapor retarder is installed it may be installed to either the interior or exterior of the building. For additional information on vapor retarders refer to the vapor retarder section on pages 13 and 14.