States like California that have prioritized efficiency have achieved significant energy savings. Codes and standards have traditionally been the largest driver for efficiency in Californian residential and commercial buildings.
“Naturally occurring” efficiency, though significant, is not a driver for efficiency savings. These are savings achieved in the business-as-usual environment, such as replacing an old worn-out furnace with one that meets current federal equipment standards.
Kavalec, Chris, and Tom Gorin. 2009. California Energy Demand 2010-2020 Adopted Forecast. Sacramento, CA: California Energy Commission.