Bay Area region / California
Portola Valley ADU rules
& permit guide.
Planning an ADU in Portola Valley? 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
External ADU: 800 to 1,500 square feet depending on proposed setbacks/FAR JADU: 500 square feet Internal ADU: 1700 square feet *Not more than 50% of primary dwelling square footage, unless 50% of primary dwelling is less than 800 square feet.
Setbacks
less than base zoning district: 16 feet vertical/maximum height Compliant setbacks: 18 feet vertical height/24 feet maximum height *Higher builds require discretionary approval unless preempted by State Law Setbacks Less than base zoning district: Subject to additional standards (height/size) Attached: Same as zoning for primary dwelling Detached: rear and side – 4 feet, front – same as underlying zoning unless 800 square foot unit not feasible
Parking
JADUs/Internal ADUs: None External ADUs: One parking spot required but may be shared with primary unit on parcels 1 acre or greater. Tandem parking/parking in setbacks allowed
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 Portola Valley'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?