A building project constructed by or renovated by a state agency or for occupancy or use by a state agency that is larger than 5,000 gross ft2 of occupied or conditioned space must be 10-30% more energy efficient than similar buildings on similar sites. See Energy Efficient State Building Act, 2008.
The Idaho Building Code Board has authority to adopt and amend building codes pursuant to I.C. Section 39-4109. Updated codes are adopted every three years by the Idaho Legislature as they are revised by the International Code Council.
The 2006 building and energy codes were presented for adoption by the 2007 Idaho Legislature for implementation in Idaho in July 2007.
The effective date of the 2009 IECC was January 1, 2011 (IDAPA 07.03.01.004).
Enforcement of building and energy codes is handled by local building code adopters. Energy codes for state facilities and modular prefabricated buildings are enforced by the Idaho Division of Building Safety. Public school plans may be examined by a ICC-certified examiner instead of the Division of Building Safety (2009 HB251).
On May 6, 2010, Idaho was announced as one of the states that will participate in BECP's Compliance Evaluation Pilot Study.
Idaho Residential Energy Standards (IRES) (Senate Bill [SB] 1591) was enacted in 1990 and was the only legislated statewide energy code in Idaho. However, it was a minimum standard and local jurisdictions could adopt more efficient energy codes.
A 1994 state-sponsored analysis of new construction by jurisdiction and energy code indicated that approximately 38% of housing starts were built to IRES. Five different energy codes listed below were used in the state as of late 1994:
- Idaho Residential Energy Standard (IRES)
- Northwest Energy Code (NEC), adopted by 46 jurisdictions
- Bannock County Energy Code (BCEC), based on the NEC
- Boise City Ada County energy code, based on the NEC
- IDWR's fuel-blind code for non-electrically heated homes, adopted by Lewiston.
Senate Bill 1208 was passed in March 1995 modifying the 1990 IRES to the 1996 IRES, which became effective January 1, 1996. The 1996 IRES eliminated the requirement for builder certification to the Department of Labor and Industrial Services in cities or counties that have not adopted the IRES or an alternate code.
HB 611 took effect July 1, 2000. It required that any jurisdiction that has adopted the UBC, adopt the most current version of the code, which was the 1997 UBC. In the past, a jurisdiction adopting the UBC could elect to leave out the appendix that included the energy code.
Dirk Kempthorne signed House Bill 586 on March 27, 2002, which required local governments that issue building permits and enforce building codes to adopt by January 1, 2003, the International Building Code as well as the International Energy Conservation Code.
On March 23, 2004, House Bill 756 was signed into law by Govenor Dirk Kempthorne updating the Idaho Building Code Act for the adoption of the 2003 International Building, Residential, and Energy Codes. Adoption and implementation of the 2003 IECC for all Idaho building code adopters was required by no later than January 1, 2005.
On March 26, 2007, the governor signed HB 137, which made the 2006 IECC mandatory for new buildings statewide effective January 1, 2008.
On April 17, 2009, the governor signed H0220, adopting the 2006 editions of the IBC, IRC, and IEBC, as well as reaffirming the use of the 2006 IECC.
The Building Code Board intends to adopt the 2009 editions of the above-identified building codes; however, the text of the rule that the Board will promulgate to adopt the Codes is unknown at this time and will be established based on any amendments made to the codes as determined through the negotiated rulemaking process. The Board can make no amendments to the International Residential Building Code which provide for standards that are more restrictive than those published by the International Code Council. Additionally, the Board must abide by the newly enacted state law (as expressed in House Bill 218a) that relates to the International Building Code and the International Residential Code provisions regarding the installation of fire sprinklers in single family homes and multiple family dwellings up to two (2) units.
The Division of Building Safety has multiple legislative proposals.
On March 23, 2010, the City of Nampa proposed several amendments to the planned 2009 Building Code.
On January 1, 2011, the 2009 IECC with no amendments was adopted, and all jurisdictions were required to comply.
Amendments included in Idaho's Administrative Code include but not limited to changes to the insulation and fenestration prescriptive requirements, air leakage is less than 7 air changes per hour when tested or a visual inspection option, see all amendments 
- Fenestration: Climate Zones marine 4, 5, and 6 - U-factor amended from 0.32 to 0.35
- Skylights: Climate Zones marine 4, 5, and 6 - U-factor amended from 0.55 to 0.60
- Ceiling: Climate Zones marine 4 and 5 – R-value amended from R49 to R38 and U-factors from 0.026 to 0.030
- Wood framed Wall: Climate Zone 6 – R-value amended from 20+5 or 13+10 to 20 or 13+5 and U-factors from 0.48 to 0.57
- Mass Wall: Climate Zone 6 –R-value amended for cavity insulation from R20 to R19
- Basement wall: Climate Zone Marine 4 and 5 – R-values amended from 15/19 to 10/13 and U-factors from 0.050 to 0.059
- Crawlspace: Climate Zones Marine 4, 5, and 6 – R-values amended from 15/19 to 10/13 and U-factors from 0.055 to 0.065
- Steel framed walls changes in equivalent R-values
- Air infiltration: Air tightness requirement changes from 3 ACH to 7 ACH and includes the option for a visual inspection in place of testing
- Log construction – separate minimum R-values for building envelope assemblies
- Compliance option added “REScheck” using 2012 IECC code option (no amendments)
- Lighting: Amended 75% to 50% high efficacy