Section 18.36.040.B
Dimensional standards
Height & bulk
Servicing
- Geographic extent
- ADUs prohibitedProhibitedNot allowed in the district at all, short of rezoning or a variance. on parcels <1 acreacre43,560 square feet — about the size of an American football field without the end zones. with direct vehicular access from road/cul-de-sac with single ingress/egress and width <18 ft; ADUs prohibitedProhibitedNot allowed in the district at all, short of rezoning or a variance. where construction not permitted under Geologic Regulations; ADUs in areas Y* and N* must comply with Geologic Regulations.
Uses
Permitted by right2
Extracted standards
29 individual requirements pulled out of this section’s prose, each with the sentence it came from.
Height
- Maximum heightMaximum heightThe tallest a building may be, given in feet, in storeys, or both — whichever binds first. for discretionary review
More than eighteen feet vertical height or twenty-four feet maximum height, where allowed by the base zoning district, and shall be subject to staff discretionary review.
- Maximum heightMaximum heightThe tallest a building may be, given in feet, in storeys, or both — whichever binds first. for ministerial review with complying setbacksSetbackThe distance a building must be held back from a lot line.24 ft
Eighteen feet vertical height and twenty-four feet maximum height and shall be subject to ministerial review where the setbacks comply with those of the base zoning district. This includes daylight planes, where applicable.
- Maximum heightMaximum heightThe tallest a building may be, given in feet, in storeys, or both — whichever binds first. for ministerial review with reduced setbacksSetbackThe distance a building must be held back from a lot line.16 ft
Sixteen feet vertical height and sixteen feet maximum height for an external ADU subject to ministerial review where the setbacks are less than those of the base zoning district.
Lighting
- Outdoor lighting compliance
All lighting shall comply with Section 18.36.040.A.8, outdoor lighting.
Other
- ASCC review
ADUs with a separate driveway or located in a non-residential zone shall be subject to ASCC review.
- Maximum color reflectivity40 pct
Color reflectivity values shall not exceed forty percent, except that trim colors and roofs shall not exceed fifty percent reflectivity.
- Fire safety checklist
Any proposed external ADU, which does not comply with the underlying zoning or local setbacks governing the parcel, shall comply with and submit with the ADU application a completed Town of Portola Valley Fire Safety Checklist adopted by resolution of the town council.
- Fire safety prohibition
ADUs are prohibited on parcels smaller than one acre whose direct vehicular access is from a road or cul-de-sac which (1) has a single point of ingress/egress and (2) has a width of less than eighteen feet.
- Geologic safety additional restrictions
ADUs located in areas Y* and N* shall comply with the town's Geologic Regulations.
- Geologic safety prohibition
ADUs are prohibited where construction is not permitted under Resolution No. 2746-2017 (or successive resolution or ordinance) ('Geologic Regulations') which governs construction on or near earthquake faults and traces and areas subject to active downslope movement as shown on the town's Geologic and Ground Movement Potential maps as updated from time to time.
- Maximum number of ADUs
One ADU and one JADU shall be permitted on all parcels smaller than three and one-half acres in size. Two ADUs shall be permitted on parcels three and one-half acres or larger in size as follows: one ADU must be detached from the main building and one ADU must be internal. A JADU shall be permitted in lieu of an internal ADU.
- Maximum floor area for external ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage. complying with setbacksSetbackThe distance a building must be held back from a lot line. on parcels >=3.5 acresacre43,560 square feet — about the size of an American football field without the end zones.1,500 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.
Fifteen hundred square feet for external ADUs where the proposed ADU complies with the setbacks of the base zoning district and special setbacks applicable to the parcel on parcels three and one-half acres or larger in size. If such parcel also contains an interior ADU, the maximum floor area limit of the external ADU shall not exceed twelve hundred square feet.
- Maximum floor area for external ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage. complying with setbacksSetbackThe distance a building must be held back from a lot line. on parcels <3.5 acresacre43,560 square feet — about the size of an American football field without the end zones.1,200 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.
Twelve hundred square feet for external ADUs where the proposed ADU complies with the setbacks of the base zoning district and special setbacks applicable to the parcel, on parcels smaller than three and one-half acres in size.
- Maximum floor area for external ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage. not complying with setbacksSetbackThe distance a building must be held back from a lot line. (up to 1 bedroom)850 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.
Eight hundred fifty square feet for external ADUs with up to one bedroom or one thousand square feet for external ADUs with more than one bedroom where the proposed ADU does not comply with the setbacks of the base zoning district and special setbacks applicable to the parcel.
- Maximum floor area for external ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage. not complying with setbacksSetbackThe distance a building must be held back from a lot line. (more than 1 bedroom)1,000 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.
Eight hundred fifty square feet for external ADUs with up to one bedroom or one thousand square feet for external ADUs with more than one bedroom where the proposed ADU does not comply with the setbacks of the base zoning district and special setbacks applicable to the parcel.
- Maximum floor area for internal ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage.1,700 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.
Seventeen hundred square feet for internal ADUs on all parcel sizes.
- Maximum floor area for JADU500 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.
Five hundred square feet for JADUs on all parcel sizes.
- External ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage. floor area percentage limit50 pct
An external ADU shall be additionally limited to fifty percent of the floor area of the existing or concurrently proposed main building, except as necessary to enable an ADU up to eight hundred and fifty square feet for external ADUs with up to one bedroom or one thousand square feet for external ADUs with more than one bedroom.
- Ministerial review
State exemption ADUs and ADUs without conditions listed in Section 18.36.040.B.6.b–d shall be subject to ministerial review.
- Landscaping with native plants
Landscape plantings shall be selected from the town's list of approved native plants and shall adhere to the town's landscaping guidelines, as described in the design guidelines.
- Prohibition on separate sale
ADUs and JADUs shall not be sold separately from the main dwelling.
- Owner occupancy requirement
Where there is an ADU, either the ADU or the main building must be owner occupied. The other unit may be rented. ADUs approved between January 1, 2020 and December 24, 2024 are excepted from this requirement. Where there is a JADU, either the JADU or the main building must be owner occupied.
- Minimum rental term30 days
On properties where an ADU or JADU is present, any rentals of the ADU, JADU, or main building shall be for a term of thirty days or more.
- SetbackSetbackThe distance a building must be held back from a lot line. for converted garage0 ft
No setback shall be required for an existing garage that is converted to an accessory dwelling unit. This shall apply to both conforming and legal non-conforming garages.
- SetbackSetbackThe distance a building must be held back from a lot line. for external ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage. up to 850/1000 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.4 ft
A setback of four feet from the side and rear lot lines shall be required for an external ADU of up to eight hundred fifty square feet with up to one bedroom or one thousand square feet with more than one bedroom.
- Staff discretionary review
ADUs with a light well larger than the minimum building code requirement shall be subject to staff discretionary review.
- Utility undergrounding requirements
Utilities shall be required to be placed underground, as described in Section 18.36.010.B, with exceptions for internal ADUs and detached ADUs connecting from main house.
Parking
- Parking requirement for external ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage.1 spaces
External ADUs shall require one dedicated parking space, as follows: ADU parking may be located in a covered or uncovered space, in tandem with other parking, and/or in setbacks. On parcels of one acre or larger where an ADU of twelve hundred square feet or less is proposed, ADU parking is not required to be dedicated.
- Parking requirement for internal ADUAccessory dwelling unit (ADU)A second, smaller home on a lot that already has one — a garage flat, basement flat or backyard cottage. and JADU0 spaces
JADUs and internal ADUs shall not require any dedicated parking spaces.
From the ordinance
ADUs and JADUs shall be permitted on all parcels in all zoning districts, where a main building is in existence or is proposed concurrently.
Parking requirements
{
"JADU": "0 spaces",
"external ADU": "1 space",
"internal ADU": "0 spaces"
}