Energy efficiency requirements in energy codes vary across states, with states having adopted energy codes ranging across editions of the industry consensus standard (ASHRAE 90.1). Some states do not have a code requirement for energy efficiency, leaving it up to the locality or jurisdiction to set its own requirements. This paper uses ASTM building economic standards (E917-05(2010) and E1074-09) to estimate the impacts that the adoption of more stringent energy codes for commercial buildings would have on building life–cycle costs. The results are based on analysis of the Building Industry Reporting and Design for Sustainability (BIRDS) database. For this study, the performance of buildings designed to meet current state energy codes is compared to their performance when meeting a “Low Energy Case” (LEC) building design based on ASHRAE 189.1-2009, which increases energy efficiency beyond the ASHRAE 90.1-2007 design, to determine whether more stringent energy standard editions are life–cycle cost–effective in reducing energy consumption. The approach is described in detail for a single city and building type (Knoxville, TN). Using the same approach, the new savings for each building type in all cities for Tennessee are calculated. The estimated average savings for each of the building types are aggregated using state–level new commercial building construction data to calculate the magnitude of the net savings (80.8 GWh annually and $28.1 × 10⁶ in life-cycle costs) that Tennessee may realize if it were to adopt the LEC design as its state energy code. These state-level estimates are further aggregated to the national level, estimating the potential total impact from nationwide adoption of the LEC design to be 34 441 GWh and $1.0 billion for 1 years' worth of construction for a 10-year study period.