Portola Valley Municipal Code Ch. 18.25 Standards for Accessory Dwelling Units (ADU) and Junior Accessory…

The purpose of this chapter is to implement Government Code Sections 66310 through 66342 by allowing the creation of accessory dwelling units (ADUs) or junior accessory dwelling units (JADUs) through ministerial review. In the event of any conflict or discrepancy between the ADU or JADU standards in this chapter and any other provisions of this title, the standards contained in this chapter shall take precedence. Ambiguities or gaps in this chapter shall be resolved first by reference to Government Code Sections 66310 through 66342. In the event of any conflict between state law and this chapter, Government Code Sections 66310 through 66342 shall govern.

(Ord. 2026-455, § 2 (Exh. A), 2026)

For the purposes of this chapter the definitions as described in California Government Code Section 66313, or as amended shall apply.

(Ord. 2026-455, § 2 (Exh. A), 2026)

A. Building Permit Required. All ADUs or JADUs, including those that are internal to an existing structure and converted from existing floor area, shall be subject to a building permit.

B. Permitting Procedure.

1. Ministerial Review. A permit application for an ADU or JADU shall be processed ministerially, without discretionary review or a hearing.

2. Completeness Determination. A permit application for an ADU or JADU shall be determined to be complete or incomplete and a written notice of the determination provided not later than fifteen business days after receiving the application. If the town determines that an application is incomplete, the town will provide the applicant with a list of incomplete items and a description of how the application can be made complete in the written notice. If a permit application is determined to be incomplete or is denied, the applicant may appeal that decision. After receipt of the appeal, the town shall provide a final written determination within sixty business days.

3. Review Period.

i. ADU on a Lot with an Existing Dwelling. If there is an existing single-family or multi-family dwelling on a lot, a permit application for an ADU or JADU shall either be denied or approved within sixty days of receipt of a complete application.

ii. ADU Accompanying Application for a New Primary Dwelling. If a permit application to create an ADU or JADU is submitted with a permit application to create a new single-family or multi-family dwelling on a lot, the town may delay approving or denying the permit application for the ADU or JADU until the town approves or denies the permit application to create the new single-family or multi-family dwelling; however, the application to create the ADU or JADU shall be considered without discretionary review or hearing.

iii. If the applicant requests a delay, the sixty-day time period shall be tolled for the period of the delay.

4. Deemed Approved. If a complete application is not approved or denied within sixty days of receipt of a complete application, the application shall be deemed approved.

5. Denied Applications. If an application for an ADU or JADU is denied within sixty days of receipt of a complete application, the town shall return in writing a full set of comments to the applicant with a list of items that are defective or deficient, and a description of how the application can be remedied.

6. Nonconforming Conditions. No application for a permit to create an ADU or JADU shall be denied due to the correction of nonconforming zoning conditions, building code violations, or unpermitted structures that:

i. Do not present a threat to public health and safety; and

ii. Are not affected by the construction of the ADU or JADU.

(Ord. 2026-455, § 2 (Exh. A), 2026)

A. Fire Sprinklers. ADUs and JADUs shall not be required to provide fire sprinklers if fire sprinklers are not required for the primary residence. The construction of an ADU or JADU shall not trigger a requirement for fire sprinklers to be installed in the existing primary dwelling or existing multi-family dwelling.

B. Short-Term Rental Limitation. ADUs and JADUs shall not be rented for a term of less than thirty days.

C. Replacement Parking. Replacement parking shall not be required when a garage, carport, covered parking structure, or uncovered parking space is demolished in conjunction with the construction of an ADU or JADU or converted to an ADU or JADU. A demolition permit for a detached garage to be replaced with an ADU or JADU shall be reviewed and issued concurrently with the ADU or JADU permit application.

D. Separate Sale. Except as permitted by Government Code Section 66341, as the same may be amended from time to time, ADUs shall not be sold or conveyed separately from the primary dwelling.

E. Utility Connection.

1. Availability of Utilities. All ADUs shall be connected to public utilities or their equivalent including water, electricity, and sewer services. In the case of well water systems and septic systems the applicant must demonstrate that they are adequately sized for the new demand. Utility connections are subject to review and approval by the appropriate utility agency.

2. ADUs using a private sewage disposal system shall obtain approval by the local health officer.

3. ADUs constructed pursuant to paragraph (1) of subdivision (a) of Government Code Section 66323 shall not be required to install a new or separate utility connection directly between the ADU and the utility, unless the ADU was constructed with a new single-family residence, or upon separate conveyance of the ADU pursuant to Government Code Section 66342. For all other ADUs the service provider may require a new or separate utility connection directly between the ADU and the utility.

4. JADUs shall not be required to install a new or separate utility connections.

5. Except for ADUs permitted pursuant to Government Code Section 66323, when a new or separate utility connection directly between the ADU and the utility is proposed, the utility connection shall be placed underground consistent with Section 18.36.010.B.

F. Separate Entrance. ADUs and JADUs shall provide at least one exterior entrance that is separate from the main entrance of the primary dwelling.

G. Separate Address. ADUs and JADUs shall provide a separate address from the primary dwelling, except for JADUs which have an interior entry to the main living area of the single-family residence.

H. Public Health and Safety. Nothing in this code shall be construed as overriding any provision of state law allowing denial of an ADU for impacts to public health and safety.

(Ord. 2026-455, § 2 (Exh. A), 2026)

A. Connection Fees or Capacity Charges. An ADU shall not be considered a new residential use for the purposes of calculating connection fees or capacity charges for utilities, including water and sewer service, unless the ADU was constructed with a new single-family dwelling. These fees are assessed by the utility agency.

B. Impact Fees. Impact fees shall not be imposed on an ADU that is less than seven hundred fifty square feet in interior livable space. For all other ADUs, impact fees shall be charged proportionate to the square footage of the primary dwelling unit. Impact fees shall not be imposed on a JADU.

C. School Fees. Consistent with Section 17620 of the Education Code, an accessory dwelling unit or junior accessory dwelling unit that contains less than five hundred square feet of interior livable space shall, be considered other residential construction that does not increase assessable space by five hundred square feet. These fees are assessed by the school district.

(Ord. 2026-455, § 2 (Exh. A), 2026)

A. General Plan and Zoning.

1. Residential Use. ADUs approved in compliance with this chapter shall be considered a residential use that is consistent with the existing general plan and zoning designation for the lot.

2. Permitted Locations. ADUs are permitted on lots with an existing or proposed single-family or multi-family dwelling in areas zoned to allow single-family or multi-family residential use.

3. Density. ADUs shall not count toward the maximum density permitted on the lot.

B. ADU Typology. ADUs shall be either:

1. Attached to, or located within, the proposed or existing primary dwelling, including attached garages, storage areas or similar uses or an accessory structure; or

2. Detached from the proposed or existing primary dwelling and located on the same lot as the proposed or existing primary dwelling, including detached garages.

C. Objective Standards.

1. Single-Family ADUs.

i. The following accessory units shall be ministerially approved on a lot with a single-family dwelling:

a. One ADU within the proposed space of a single-family dwelling or existing space of a single-family dwelling or existing accessory structure that may include an expansion of not more than one hundred fifty square feet for ingress/egress; and

b. One detached, new construction, ADU of not more than eight hundred square feet of interior livable space that does not exceed four-foot side and rear yard setbacks and that meets the height requirements of this chapter.

ii. One ADU that does not meet the criteria of subsection C.1.i. above may be ministerially approved if it meets the objective standards contained in this chapter, except that the minimum or maximum size for an ADU or limits on lot coverage, floor area ratio, open space, front setbacks, and minimum lot size, for either attached or detached dwellings, shall not be imposed if they preclude a unit authorized by Government Code Section 66321(b)(3) from being constructed in compliance with all other local development standards.

2. Multi-family ADUs.

i. The following units shall be ministerially permitted on a lot with a multi-family dwelling:

a. Conversion ADUs. A minimum of one ADU and a maximum of twenty-five percent of the total number of existing multi-family dwelling units shall be permitted to be converted from existing multi-family dwelling structures that are not used as livable space, including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages, if each unit complies with the state building standards for dwellings.

b. Detached ADUs.

(1) Existing Multi-family Dwelling. On a lot with an existing multi-family dwelling, not more than eight detached ADUs shall be permitted. The number of ADUs shall not exceed the number of existing multi-family units on the lot. An ADU subject to this provision shall meet the height requirements of this chapter.

(2) Proposed Multi-family Dwelling. On a lot with a proposed multi-family dwelling, not more than two detached ADUs shall be permitted. An ADU subject to this provision shall meet the height requirements of this chapter.

3. Size. Except for ADUs permitted pursuant to Government Code Section 66323, the maximum allowable square footage for ADUs shall not exceed the area limitations specified below. For the purposes of this section, the calculation of ADU square footage shall not include garages, carports, covered porches/patios, breezeways, and/or other accessory structures.

i. Existing Floor Area. ADUs converted from existing floor area shall not be subject to any size limitations.

ii. New Floor Area.

a. Attached and Detached ADUs. ADUs created from new floor area shall not exceed one thousand two hundred square feet of interior livable space. Multi-family ADUs consistent with Government Code Section 66323 shall not be subject to the size limitation of this section.

4. Adjusted Maximum Floor Area (AMFA), Lot Coverage, Floor Area Ratio (FAR) and Coverage Area Ratio (CAR).

i. ADUs count towards and shall not exceed the AMFA, lot coverage, FAR or CAR for the subject parcel. However, this shall not prohibit the ministerial approval of ADUs constructed pursuant to Government Code Section 66323 and in compliance with all other local development standards. Development of the site may exceed the AMFA, lot coverage, FAR, or CAR by the minimum amount necessary to allow such an ADU.

5. Height.

i. Existing Floor Area. ADUs converted from existing floor area shall not be subject to height limitations.

ii. New Floor Area.

a. Attached ADUs. Attached ADUs created from new floor area shall not exceed a height of twenty-five feet or the maximum height permitted in the underlying zoning district, whichever is lower. In all cases, ADUs shall not exceed two stories.

b. Detached ADUs. Detached ADUs created from new floor area, on a lot with an existing or proposed single-family or multi-family dwelling unit, shall not exceed a height of sixteen feet, or a height of eighteen feet if either of the following conditions are met:

(1) Transit Proximity. The lot on which the ADU will be created is within one-half mile walking distance of a major transit stop or a high-quality transit corridor, as those terms are defined in Public Resources Code Section 21155.

(2) Multi-family, Multi-story Structure. The lot on which the ADU will be created consists of an existing or proposed multi-family, multi-story dwelling. An additional height of two feet, for a maximum height of either eighteen or twenty feet, shall be allowed to accommodate a roof pitch on an ADU that is aligned with the roof pitch of the primary dwelling unit.

6. Setbacks.

i. Existing Floor Area. ADUs located within an existing living area or an existing accessory structure, or ADUs that replace an existing structure and are in the same location and to the same dimensions as the structure being replaced, shall not be subject to setbacks.

ii. New Floor Area. ADUs created from new floor area are subject to the following setbacks:

a. Front Yard. Same as the underlying district, including required scenic corridor setbacks. No front setback is required for ADUs permitted per Government Code Section 66323.

b. Side Yard. A minimum of four feet.

c. Rear Yard. A minimum of four feet.

7. Parking.

i. Parking shall not be required for ADUs.

ii. If parking is provided, parking space design shall conform with Section 18.60.020, Parking dimensions and access.

8. Site improvements. Site improvements, including grading, driveways, patios, decks, etc., outside the minimum necessary to facilitate the construction of an ADU pursuant to Government Code Section 66323 shall be subject to the requirements and permitting processes of the underlining zoning district for such improvements.

9. Objective Design Standards. ADUs (except those created pursuant to Government Code Section 66323) shall comply with the following objective design standards. ADUs created pursuant to Government Code Section 66323 are encouraged, but not required, to comply with the objective design standards of this section.

i. Light Reflectivity Values (LRV). The LRV of proposed colors shall not exceed forty percent, except that trim color and roofs shall not exceed fifty percent.

ii. Exterior Lighting. All exterior lighting shall comply with all requirements listed in Section 18.36.040.A.8, Outdoor lighting, except that the primary entrance of the ADU may have one or two fixtures, which shall be limited to a total lumen count of seven hundred lumens.

iii. Landscaping. Proposed landscaping plantings shall be selected from the town's approved native plants list.

D. Building Code Requirements. ADUs must comply with the town's building code requirements for detached dwellings. However, constructing an ADU does not constitute a group R occupancy change under Section 310 of the California Building Code (Title 24), unless the building official issues a written finding, supported by substantial evidence, that the construction poses a specific, adverse impact on public health and safety. This provision shall not prevent the town from changing the occupancy code for space converted from uninhabitable or non-residential use to residential use.

E. Passageway. No passageway shall be required in conjunction with the construction of an ADU.

(Ord. 2026-455, § 2 (Exh. A), 2026)

A. Permitted Locations. JADUs shall be permitted in single-family residential zones.

B. Number of JADUs. The following accessory units shall be ministerially approved on a lot with a single-family dwelling. This is in addition to the ADUs allowed per Section 18.25.060.

1. One JADU within the proposed space of a single-family dwelling or existing space of a single-family dwelling that may include an expansion of not more than one hundred fifty square feet for ingress/egress.

C. Size. JADUs shall be limited to a maximum size of five hundred square feet of interior livable space.

D. Owner Occupancy. Owner occupancy is required if the JADU has shared sanitation facilities with the primary dwelling. The owner may reside in either the JADU or the primary dwelling unit. Owner-occupancy is not required if the JADU has separate sanitation facilities from the primary dwelling unit or if the owner is another governmental agency, land trust, or housing organization.

E. Deed Restriction. A deed restriction, which shall run with the land, shall be filed with the town. The deed restriction shall include:

1. A prohibition on the sale of the JADU separate from the sale of the single-family residence, including a statement that the deed restriction may be enforced against future purchasers; and

2. A restriction on the size and attributes of the JADU that conforms with Government Code Sections 66333 through 66339.

F. Interior Entry. In addition to a separate exterior entrance, JADUs that do not include a bathroom shall include an interior entry to the main living area of the single-family residence.

G. Efficiency Kitchen. JADUs shall provide an efficiency kitchen that includes all of the following:

1. A cooking facility with appliances.

2. A food preparation counter and storage cabinets that are of reasonable size in relation to the size of the JADU.

H. Parking. Parking shall not be required for a JADU.

I. New or Separate Unit. JADUs shall not be considered a separate or new dwelling unit for the purposes of any fire and life protection ordinance or regulation.

(Ord. 2026-455, § 2 (Exh. A), 2026)