The IEc team applied a mixed-methods design to evaluate the US DOE’s Building America (BA) program, a residential large-scale technology demonstration, peer-to-peer information exchange and market diffusion program for residential energy efficiency (EE) technologies and practices. BA advanced the systems engineering, whole house approach to residential EE that has become the standard practice. BA’s marque intervention is the use of building teams, comprised of production homebuilders and building science experts, that work together to conduct large scale demonstrations of EE practices and refine approaches until they are cost-effective.1 Many EE construction approaches have gained market acceptance as a result of BA’s work, including the air tightness, duct tightness, envelope insulation, and thermal bridging requirements that were integrated into EnergyStar Homes and into IECC model energy code.