What once might have been broad assumptions about the merits of energy efficiency provisions in building codes now have the backing of research. A San Francisco-based organization called Climate Policy Initiative recently completed an analysis that compares states with energy codes to those without.The results (click here for a PDF of the full, 23-page report) show that homes built when state energy codes were in effect are, on average, 10% more energy efficient, derive a greater share of their energy from natural gas (reflecting code provisions that encourage high-efficiency gas units and electric heat pumps), and, on a per-house basis, average 16% lower greenhouse gas emissions than homes built in locations where there was no energy code. In 2008, that per-house reduction in emissions reduced overall residential building emissions by about 1.8%, the study found.CPI researchers compiled a nationwide survey of state energy codes, analyzed energy consumption data of the homes in each state, and compared that data with energy use estimates based on building simulation models (which assumed perfect code compliance). The researchers acknowledge that reductions in energy use can be influenced by a number of factors other than code – including appliance standards and utility incentive programs – but also noted that engineering estimates of code-driven energy savings tended to be fairly conservative.Motivation for the researchThe CPI points out that residential buildings consume about 22% of the nation’s “primary energy” – reflecting their total energy footprint, including the embedded energy in fossil fuels before they are refined for sale to consumers – and produce about 21% of the country’s carbon emissions.Forty of the 50 states have adopted residential building energy code, in most cases a version of the International Energy Conservation Code, which is revised every three years. Some states, notably California, Florida, Oregon, and Washington, have adopted more-stringent standards. The Department of Energy analyzes each model code to evaluate its potential effectiveness, and each state is required to assess whether the model codes that are shown to be effective would be appropriate for adoption. But states are not required to adopt the code. Among those that haven’t, however, are some that promote voluntary adoption or adoption by local governments.Although the first widely adopted residential building code was the American Society of Heating, Refrigerating, and Air Conditioning Engineers’ standard 90-75 of 1975, the code most builders are familiar with is some version of the IECC standards that began appearing in 1998 and recently saw publication of their fifth update, the 2012 IECC. Homes built in compliance with the 2012 version are expected to be 30% more energy efficient than those built to the IECC 2006 standard, the DOE notes.