The International Energy Conservation Code is increasingly the standard energy code that municipalities are adopting. In prescribes insulation (r-value) requirements for both residential and commercial buildings.
In order to determine what your required insulation values are, you must first determine which of the climate zones you fall in. In Colorado it is highly dependent on the county and we actually have 4/8 zones present in the state.
Baca, Las Animas and Otero Counties are in Zone 4.
Alamosa, Archuleta, Chaffee, Conejos, Costilla, Custer, Dolores, Eagle, Moffat, Ouray, Rio Blanco, Saguache and San Migual are in Zone 6.
Clear Creek, Grand, Gunnison, Hinsdale, Jackson, Lake, Mineral, Park, Pitkin, Rio Grande, Routt, San Juan and Summit County are in Zone 7.
The remaining counties are in Zone 5.
Once you have the Zone and the construction type, you can consult the charts to determine the insulation requirements for each assembly. The various options are too numerous to list without simply posting the code. If you have any specific questions or need a list of counties outside of Colorado, comment on the post or email me.