Flood damages occur when just one inch of water enters a residential household, and models of flood damage estimation are sensitive to first-floor elevation (FFE). The current sources for FFEs consist of costly survey-based elevation certificates (ECs) or assumptions based on year built and foundation type. We sought to address these limitations by establishing the role of an RTK enabled UAS to efficiently derive accurate FFEs. Four residential communities within Galveston Island, Texas were selected to assess efficient flight parameters required for UAS photogrammetry within the built environment. A DJI Phantom 4 RTK was then used to gather georeferenced aerial imagery and create detailed 3D photogrammetric models with +0.02 m horizontal and +0.05 m vertical accuracies. From these residential models, FFEs and other measurements present in traditional ECs were obtained. Comparative statistical analyses were performed using the UAS-based measurements and traditional EC measurements. UAS based FFE measurements achieved 0.16 m mean absolute error (MAE) across all comparative observations and were not statistically different to traditional EC measures. Given that aerial imagery capture, photogrammetric processing, and deriving of FFEs for each community were completed within a week, our study concludes the RTK enabled UAS approach is an efficient, cost-effective method in establishing accurate FFEs and other flood sensitive measures in residential communities. FFEs, along with other UAS-based data, can be used to parametrize flood risk models further and understand damage at the household level.