Calls are mounting for a Senate floor vote on the Energy Savings and Industrial Competitiveness Act of 2011 (generally referred to as the Shaheen-Portman bill). The bill introduces a variety of measures that encourage or facilitate energy efficiency in residential and commercial buildings. These include a section that strengthens the Department of Energy’s authority to require that national model energy codes attain deep energy savings. Before becoming law, these model codes must be adopted at the state (or sometimes local) level; most states do adopt them. Do these codes work? Do they help households and businesses save money and energy? Evidence shows that they do. CPI’s own research indicates that codes work. Our analysis demonstrates that past U.S. residential building codes have successfully saved the energy they were projected to, and perhaps even more. Several other analyses (subscription required to access in some cases) have similarly found that projected code savings do occur. Moreover, from a climate perspective, CPI found that past codes have not only saved energy but also shifted household fuel use towards lower-emissions natural gas. Therefore, codes have saved a greater share of household emissions than of household energy. Model code provisions that encourage this shift were removed in the 2009 residential model code, but (partially) returned to the 2012 residential model code. On the cost side, DOE just released a study of the cost-effectiveness of the 2009 and 2012 residential model energy codes last week. The study finds that the 2009 and 2012 codes are expected to be very cost-effective: When financed through a typical mortgage, they pay themselves back within 1-2 years for both codes, across every climate zone in the U.S. This study uses detailed current data on component-by-component costs of home construction, which provides better and more reliable evidence of actual costs than any previous work. Retrospective analysis of code impacts on housing costs could confirm these projections. Nevertheless, given that the energy savings from the codes have been realized, there is no particular reason to doubt the findings. Past experience is no guarantor of future performance, but the evidence shows that residential building energy codes have performed well in the past, and the best current analysis suggests that they will continue to perform well in the future. Policy that strengthens their reach would appear to be well-justified.