Digital Twins for Accessory Dwelling Unit Feasibility under Environmental and Infrastructure Constraints: The Case of Austin, Texas

Accessory Dwelling Units (ADUs) have emerged as a widely adopted tool for adding infill housing in U.S. cities, yet most feasibility assessments remain limited to zoning eligibility, whether a given lot is legally permitted to host an ADU. What zoning-only tools cannot show is where regulatory permission translates into practical buildability, and where it does not. This study develops a GIS-based digital twin framework that integrates zoning regulations with environmental constraints, including flood risk, impervious cover limits, tree-protection rules, and drainage conditions, to provide a more complete and spatially explicit picture of parcel-level ADU feasibility. Austin, Texas serves as the case study, given the city’s recent ADU policy reforms under the HOME Initiative and its pronounced spatial variation in environmental conditions across neighborhoods. The results demonstrate that the digital twin substantially narrows the estimate of feasible ADU parcels compared to zoning-only analysis. In East Austin (78702), 39% of single-family-zoned parcels are classified as ineligible once environmental constraints are applied, nearly double the rate in Brentwood/Crestview (78757) at 22%. These disparities are driven primarily by lot coverage, floodplain exposure, and protected tree conflicts, which are unevenly distributed across neighborhoods. Notably, East Austin also leads the city in total ADU completions (666 built), a pattern that reflects the overriding role of property values and investment capacity in driving development outcomes, a dimension that environmental data alone cannot explain, but that the digital twin makes spatially legible by distinguishing between parcels where constraints are the binding limit and parcels where they are not. The primary contribution of this study is the digital twin framework itself: a replicable, open-data approach to visualizing regulatory and environmental factors that shape ADU feasibility at the parcel scale. By making these constraints explicit and interactive, the platform supports more transparent planning practice, enables planners to identify where clusters of constrained parcels may benefit from targeted infrastructure investment, and provides homeowners with actionable, site-specific feasibility information that zoning maps cannot offer.