Staten Island’s low-density neighborhoods present an opportunity to address the housing shortage and rising residential emissions through small-scale urban infill. This project proposes a flexible, carbon-storing ADU built from standardized panels of locally harvested common reed, creating adaptable layouts that respond to varying lot sizes, orientations, and privacy needs. With three unit options, the system supports multiple relationships between private and communal outdoor spaces while optimizing sunlight, shading, and natural cross ventilation. As a fast-growing wetland plant, common reed offers durability, thermal insulation, and carbon sequestration, making it an effective low-carbon building material. By transforming an underutilized invasive species into a renewable construction material, the project stores carbon directly within the building envelope while reducing transportation emissions and supporting local marsh management. Scalable across Staten Island’s suburban lots, the reed ADU system offers a low-carbon housing model that leverages local biomaterials to support both environmental resilience and neighborhood densification.