Lot Coverage Limits: San Mateo vs South San Francisco
How do lot coverage limits rules compare between San Mateo, CA and South San Francisco, CA?
San Mateo and South San Francisco have similar restriction levels.
San Mateo, CA
San Mateo County
San Mateo regulates lot coverage through Title 27 of the zoning code. Maximum lot coverage and floor area ratio vary by zone district. ADUs of at least 800 square feet with 16-foot height and 4-foot setbacks may be built regardless of lot coverage, FAR, or open space limitations per state law.
View full San Mateo rules →South San Francisco, CA
San Mateo County
Lot coverage and floor-area limits in unincorporated San Mateo County are district-specific. Several residential districts cap building site coverage at 25 percent and floor-area ratio around 30 percent (or a minimum square-foot allowance), with stricter standards in some areas.
View full South San Francisco rules →Key Facts Comparison
| Fact | San Mateo | South San Francisco |
|---|---|---|
| Regulation | Coverage + FAR + open space | - |
| ADU Override | 800+ sq ft ADU exempt from coverage | - |
| Daylight Plane | Additional height/massing control | - |
| Code Reference | SMMC Title 27 zone standards | - |
| Contact | Community Development — 650-522-7200 | - |
| Common residential coverage | - | 25% of building site (e.g., Sec. 8.110.070) |
| Floor-area ratio (example) | - | 30% of site or 2,400 sq ft, whichever greater |
| COSC district | - | 10% coverage, 2-acre min, 16 ft height |
| Midcoast impervious | - | Limited to ~10% of parcel size |
| Counts toward coverage | - | Buildings, decks/patios 18+ inches high |
| Varies by | - | District, 'S' overlay, Coastal/Design Review |
Highlighted rows indicate differences between cities.
San Mateo FAQ
What is the lot coverage limit in San Mateo?
It varies by zone district. Both lot coverage percentage and floor area ratio limits apply. Check the development standards for your specific zone in Title 27.
Can I build an ADU even if I am at max lot coverage?
Yes. State law and Chapter 27.19 allow ADUs of at least 800 square feet with 16-foot height and 4-foot setbacks regardless of lot coverage or FAR limits.
What is FAR?
Floor Area Ratio measures total floor area of all stories relative to lot area. It limits building bulk independently of lot coverage percentage.
South San Francisco FAQ
How much of my lot can I cover with buildings?
It depends on the district. Many residential districts cap building site coverage at 25 percent (counting buildings and raised decks/patios) with a floor-area ratio around 30 percent. Some areas, like COSC and the Midcoast, are stricter.
Do decks and patios count toward lot coverage?
Yes. Under standards like Section 8.110.070, structures such as patios, decks, balconies, and porches that are 18 inches or more above the ground count toward the building-site coverage limit.
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