San Mateo County, CA Building Setbacks & Zoning: Setback Rules (2026)

Setbacks in unincorporated San Mateo County are set by a combination of the base district (such as R-1) and a combining 'S' (Residential Density / site) district that is mapped on the Zoning Maps. The base residential yard rules (Section 8.68.030, for the R-E district, which mirrors the general residential pattern) require each lot to have side yards of not less than 5 feet, a rear yard of not less than 20 feet, and a front yard 'as specified by any combined S District regulation, or as set forth on the Zoning Maps,' with the mapped front yard governing over conflicting provisions. Because front-yard depth is district-specific, the same county can have very different front setbacks from one neighborhood to the next. Some districts set their own figures: for example, the Planned Agricultural District (Section 8.106.100) requires a 30-foot front, 20-foot side, and 20-foot rear yard for agricultural development, and 50-foot front yards for non-agricultural development. Chapter 8.340 allows limited projections into required yards — cornices, eaves, and chimneys up to 2 feet; fire escapes up to 4 feet; and uncovered stairs or porches up to 6 feet into a front yard and 3 feet into side or rear yards — without violating the setback. Use-permit exceptions can reduce front setbacks in limited circumstances. Always check the specific parcel's zoning, combining 'S' district, and the Zoning Maps with the Planning and Building Department.