Table of Contents

• ADUs/JADUs AND THEIR BENEFITS
• QUICK OVERVIEW: TOWN ADU REQUIREMENTS
• QUICK OVERVIEW: HOW TO BUILD AN ADU/JADU IN TOWN
• FREQUENTLY ASKED QUESTIONS 
• CONTACT INFORMATION AND ADDITIONAL RESOURCES

QUICK OVERVIEW: TOWN ADU REQUIREMENTS

For detailed Municipal Code information, see Section 18.36.040.B

SIZE:

JADU: Up to 500 sq ft

Internal ADU: Up to 1,200 sq ft (or up to 1,700 sq ft with discretionary review)

External ADU (conforming to Town standards for setbacks/etc., <3.5 acres): Up to 1,200 sq ft

External ADU (conforming to Town standards for setbacks/etc., >3.5 acres): Up to 1,500 sq ft

External ADU (not conforming to Town standards): 850 sq ft (studio/1BR); 1,000 sq ft (2+BR)

SETBACKS:

Properties <1 acre: 20' front, 10' sides/rear (Town standards), 4' sides/rear (State standards)

Properties >1 acre: 50' front, 20' sides/rear (Town standards), 4' sides/rear (State standards)

Note that other requirements apply if the project uses the State standards rather than Town standards.

NUMBER OF UNITS ALLOWED:

Properties <3.5 acres: (1 External or 1 Internal ADU) + (1 JADU) = 2 units total

Properties >3.5 acres: (1 Detached ADU) + (1 Internal ADU) + (1 JADU) = 3 units total

PARKING:  External ADUs require one off-street parking space that can be uncovered, in tandem with other parking, and/or in setbacks. For properties >1 acre where the ADU is under 1,200 sq ft the parking space may overlap with guest parking. Internal ADUs/JADUs do not require a dedicated parking space.

SEWER/SEPTIC CONSIDERATIONS: Properties considering adding an ADU or JADU should carefully consider their sewer or septic system. Your system will need to have available capacity to serve your new unit, in particular if a bedroom is added. This may involve a simple hookup to an existing system, or could involve large costs with expanding a septic system or extending to a street sewer system. If on sewer, you will need to obtain approval and any required permits from the West Bay Sanitary District. You are required to submit the application and pay fees directly to the County Environmental Health Department for septic systems and West Bay Sanitation District for sewer service. 

ELECTRICAL UTILITIES: 

Attached/Internal ADU/JADU - no undergrounding required

Detached ADU - if connection is from main house, required to underground utilities on private property from main house

SAFETY RESTRICTIONS:

FIRE:  Certain parcels in Portola Valley may be restricted in development due to fire safety codes, such as street ingress/egress, slope, width of road and other conditions. Check with WFPD for code requirements

GEOLOGIC:  Certain parcels may be restricted in development under the Town’s geologic regulations, with respect to proximity to earthquake faults, traces and areas subject to active downslope movement as shown on the Town’s Geologic and Ground Movement Potential Maps.

CONVERSIONS: Conversions represent a potentially much more affordable way of creating an ADU or JADU on your property. A room in your home could be converted into a JADU with the addition of a bathroom, a simple efficiency kitchen, and an exterior door. A conversion that does not include a bathroom must include an interior door to access shared bathroom facilities. A previously permitted detached accessory structure could be converted into an ADU with the addition of a kitchen and bath.

The California Building Code (CBC) defines a kitchen as an area with a sink and permanent provisions for food preparation and cooking, requiring hot/cold water, a cooktop/oven, a refrigerator, food storage space (cabinets), and adequate light/ventilation. A core component is the sink with a drain larger than 1.5 inches, plus permanent hot cooking facilities, ensuring it's distinct from a wet bar. 

AMNESTY PROGRAM: In 2024 the California Legislature adopted AB 2533, a law that provides some amnesty provisions for eligible ADUs created without permits prior to 2020. The full text of the law is in Government Code Section 66323.  

For an unpermitted ADU or JADU constructed before January 1, 2020, the relief provided by AB 2533 includes the following:  

• The Town shall not deny a permit for an ADU or JADU that is in violation of California building standards (codes) or does not comply with any local ordinance regulating ADUs or JADUs. 

• The property owner applying for a permit to legalize an unpermitted ADU or JADU shall not be required to pay impact fees or connection or capacity charges except where utility infrastructure is required to comply with Health and Safety Code section 17920.3. 

• The Town is prohibited from penalizing an applicant for having the unpermitted unit, and the local agency is required to approve necessary permits to correct noncompliance with health and safety standards. 

• Upon receiving an application for permit to legalize an unpermitted ADU or JADU, an inspector from the Town may inspect the unit for compliance with Health and Safety standards and provide recommendations to comply with these standards. 

Other provisions and exceptions are incorporated in the law. Eligibility for the amnesty provided by AB 2533 depends on the type of ADU or JADU, the date of the ADUs construction, and various other factors. The process of applying for amnesty for an unpermitted unit is the same as an application for a new ADU. Before submitting an application for a permit for an ADU or JADU created without permits, a homeowner may obtain a confidential third-party code inspection from a licensed contractor to determine the unit’s existing condition or potential scope of building improvements before submitting an application for a permit.  Please consult with the Planning and Building Department for more information about the permit process.