A zoning overlay applied to sloped properties that imposes additional design, grading, and engineering requirements.
ADUs in hillside zones often require soils reports, retaining walls, special foundations, and additional design review. Sites with >5% slope can add $20k-$60k to ADU costs vs flat sites.
Part of the BackyardADU California ADU Glossary — plain-English definitions of the regulatory, construction, and financing terms you'll encounter during a California ADU project.