Bay Area region / California
San Carlos ADU rules
& permit guide.
Planning an ADU in San Carlos? Review local size, setback and parking requirements, then confirm the details for your property with the permitting agency.
Local source collected 2026-05-20 · View sources
Local requirements at a glance
Min/max ADU size
One bedroom or less: 850 square feet Two+ bedrooms: 1000 square feet Conversion of existing legally established detached structures: None JADU: 500 square feet *50% of main home floor area, unless under 800 square feet (state law allows an ADU up to 800 square feet on every property)
Height
Detached ADU: 18 + 2 feet to match the main building roof pitch Detached ADU with multistory, multifamily dwelling: 18 feet Detached ADU over or under detached garage: 20 feet Attached second story: determined by base zoning
Setbacks
First floor attached and detached: Side and rear – 4 feet, Front: setbacks determined by base zoning district The second floor is attached: determined by the base zoning district The second floor is attached on reversed corner lots: rear – 5 feet
Parking
JADUs: Any parking displaced by the construction of a JADU, including full or partial conversion of an existing garage, shall be replaced ADUs: One spot may be required (tandem allowed). No parking is required if ADU involves garage conversion or is: ½ mile walking distance from public transit, in a historic district, or one block from a car-share vehicle; or when on-street parking permits are required but not offered to ADU occupants
Process
Confirm your parcel and ADU type with the local planning department, prepare the required plans, and follow the city's building permit checklist. Ask which utility, fire and site reviews apply before submitting.
Your next three steps
- Confirm the property's jurisdiction, zoning and site constraints with San Carlos's planning department.
- Discuss the ADU type, dimensions and utility needs with your designer before finalizing a layout.
- Ask the permitting agency for its current application checklist, fee estimate and review process.
2026 state-law context
ADUs and JADUs have different occupancy rules
California generally prohibits local owner-occupancy requirements for ADUs. A narrow exception applies to certain separately sold affordable ADUs. For JADUs, owner occupancy generally applies when the bathroom is shared with the main home; separate-bathroom JADUs are treated differently under 2026 law. Check the HCD handbook and your project's permit conditions.
Older local summaries may not reflect the latest state changes. Read HCD’s March 2026 handbook, pages 32–33.
Questions for your first planning conversation
- Which approval path applies to my building and ADU type?
- Do easements, trees, slope, access or fire conditions affect placement?
- Which utility upgrades and agency reviews should be included in my budget?
- Are preapproved plans available, and what site work still needs review?