This study was commissioned by the Florida Department of Community Affair’s Codes & Standards Section to determine the impacts of Florida’s Energy Code over time and recommend possible changes that would increase residential efficiency. It examines each of the 15 residential energy code cycles that have occurred during the 30-year period from 1979 to 2009, and determines the relative change in energy code efficiency and its impact on energy use and energy cost throughout the period. The study has been revised to include Florida’s 2009 supplement to its 2007 energy code to determine how its requirements compare with the requirements of Section 405 of the 2009 International Energy Conservation Code. Florida’s energy code compliance software, EnergyGauge® USA, is used to conduct annual, hourly simulations and analysis of 180 different home configurations. These results are combined with Florida’s historical energy cost data and new home construction data to determine statewide energy use and cost changes across each energy code cycle and across all years since 1979. The change in median home size over the 30-year period is also considered in the analysis.