The impetus for buildings to decarbonize and move towards radical energy and water efficiency is increasingly strong and identified as a priority within the green building sector. The tiny house movement offers an opportunity to both address the challenges of affordable housing and contribute to residential building decarbonization. Tiny houses de-emphasize mass consumption and excessive belongings and have potential to address equity issues such as gentrification by providing living spaces to low-income residents in desirable housing locations. This paper analyzes the Tiny House in My Backyard (THIMBY) project, investigating building sustainability concepts through the design-build-occupy process in a three-year-old structure. THIMBY demonstrates energy and water efficiency technologies inside an award-winning small living space (18.5 m2). THIMBY was designed to reduce energy and water use by 87 and 82% compared to California residential averages. In practice, it has reduced site energy by 88% and has emitted 96% fewer carbon emissions than a 2100 square foot California Energy Commission 2016 Title 24 minimally compliant home. We discuss the differences between design and performance of energy and water systems, which we find offer important lessons for the further expansion of the tiny house movement and other alternative and micro green housing types. We find that optimizing such houses through integration of energy and water saving technologies, home energy management systems, and strong communication between modelers, builders and occupants will be essential to achieving dramatic energy (87%), water (82%), and carbon (96%) savings.