South San Francisco has published an ADU Handout

The full Ordinance can be found here 20.350.035 Accessory Dwelling Units

Summary:

A permit will be issued as a ministerial matter without discretionary review or hearing for an accessory dwelling unit within 120 days of receiving the application if the requirements of this Chapter (“Accessory Dwelling Units”), other requirements of the Zoning Ordinance, and other applicable City codes are met.

  1. Location. Accessory dwelling units may be established on any lot in any district where a primary single unit dwelling has been previously established or is proposed to be established in conjunction with construction of an accessory dwelling unit. Only one accessory dwelling unit is permitted per primary single-family dwelling on the same lot.
  2. Development Standards. Except as provided below, accessory dwelling units shall conform to the height, landscaping, lot coverage and other zoning requirements of the zoning district in which the site is located, the development standards in this chapter, other requirements of the zoning ordinance, and other applicable City codes.
  3. Where an existing detached or attached garage is converted to an accessory dwelling unit, no setback shall be required, but the structure shall conform to height, lot coverage and other zoning requirements of the zoning district in which the site is located, the development standards in this chapter, other requirements of the zoning ordinance, and other applicable City codes.
  4. Where an accessory dwelling unit is constructed above a garage, the setback for that unit shall be five feet from the side and rear lot lines, but shall conform to height, lot coverage and other zoning requirements of the zoning district in which the site is located, the development standards in this chapter, other requirements of the zoning ordinance, and other applicable City codes.
  5. The minimum side yard and rear yard setback for a detached accessory dwelling unit is five feet, except as provided in (1) above. The minimum side yard and rear yard setback for an attached accessory dwelling shall conform to the setback requirements of the zoning district where the site is located.
  6. A detached accessory dwelling unit shall be located at least six feet to the rear of the primary dwelling unit. For detached accessory dwelling units located on corner lots, accessory dwelling units shall have the same street side yard setback as required for the primary dwelling unit in the underlying zoning district. The Chief Planner may grant exceptions based on lot characteristics.
  7. Type of Unit. The accessory dwelling unit shall provide separate, independent living quarters for one household. The accessory dwelling unit may be attached, detached, or located within the living areas of the primary dwelling unit on the lot, subject to the standards of this section.
  8. Maximum Floor Area. The total area of floor space of an attached or detached accessory dwelling unit shall not exceed 900 square feet or 50 percent of the living area of the primary unit with a maximum allowable floor area of 900 square feet.
  9. Architectural Compatibility. The accessory dwelling unit may utilize either a separate entry or the same exterior doorways as the primary unit and shall be installed in a manner as to negate an obvious indication of two units in the same structure. An accessory dwelling unit shall be designed and constructed so as to blend with and complement the existing single-family unit in terms of height, roofing, siding materials and color.

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City of South San Francisco website

City of South San Francisco Planning Division