San Mateo County ADU topic page
San Mateo County 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: 150 square feet Max detached: not to exceed 800 square feet or 35% of primary residence, up to 1,500 square feet Max attached: not to exceed 800 square feet or 50% of primary residence, up to 1,500 square feet Max JADU: 500 square feet *Additional 150 square feet...
Setbacks and parking
Side and rear: 4 feet. Front: per underlying zoning district. Minimum separation: 5 feet, can be reduced with firewalls. JADUs: No parking required ADUs: One spot may be required (tandem allowed). Outside of designated Midcoast areas, no parking required if: ½ mile...