Buildings are the dominant driver of daily and seasonal electric load cycles, and account for 40 percent of U.S. final energy use. They account for roughly 10 percent of direct U.S. CO2 emissions and roughly 40 percent once indirect emissions from electricity generation are included. This paper explores the possible evolution of this sector over the coming century, its potential role in climate action and response to climate policies, and the potential benefits of advances in building technologies for addressing climate change. The paper presents a set of scenarios based on a detailed, service-based model of the U.S. buildings sector that is embedded within a long-term, global, integrated assessment model, MiniCAM. Eight scenarios are created in total, combining two sets of assumptions regarding U.S. building service demand growth, two sets of assumptions regarding the improvements in building energy technologies, and two assumptions regarding long-term U.S. climate action - a no-climate-action assumption and an assumption of market-based policies to reduce US. CO2 emissions consistent with a 450 ppmv global target. Through these eight scenarios, the paper comments on the implications of continued growth in building service demands, the ability of efficiency measures to reduce emissions, and the strong link between decarbonization of electricity generation and building sector emissions.