San Mateo ADU topic page
San Mateo ADU Rules
Start with the official local ADU rules, then confirm lot-specific limits before requesting provider quotes.
Short answer
Start with the official local ADU rules, then confirm lot-specific limits before requesting provider quotes.
Source requirement: Official city or county rule source parsed and cited.
Local rule evidence
Size
Min: None Max ADU: No max size limit, dependent on underlying zoning FAR (allowing at least an 800 sq ft) Max JADU: 500 square feet
Setbacks and parking
Side and rear: 4 feet Front: Set by underlying zoning Separation from main residence (detached): 4 feet Daylight Plane: meet R1 daylight plane from side and rear property line JADUs: No parking required ADUs: One spot unless ADU meets one of the State law exemptions