In this project,the Alliance for Residential Building Innovation team worked with builders in California to implement wall assemblies meeting a U-value lower than 0.050 Btu/h-ft2-°F. ARBI and its project team members helped builders identify preferred wall designs that met the requirements of their architects, structural engineers, and purchasing agents and that were acceptable to their subcontractors. Construction methods were observed and documented and construction costs obtained from builders were used to inform cost estimates for a range of advanced wall system types and insulation types. Wall framing types of 2 × 6 (16- and 24-in. on center [o.c.]) and double stud were modeled in Building Energy Optimization (BEopt™) software with cavity insulation levels ranging from R-19 to R-33 (double stud) and exterior rigid insulation of R-4, R-6, and R-8.