STATEWIDE UPDATE: New California ADU Bills SB13, AB68, AB881, AB670 have passed. These laws will create more options for building an ADU in San Carlos in 2020. To prepare for the upcoming changes use our ADU Services to learn how these laws will effect your property!
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San Carlos ADUs

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San Carlos ADU Guidelines Last Updated 08/11/19


The city government of San Carlos will approve ADUs under California's statewide mandated regulations.
The California Building Code (CBC) 2016 without amendments is adopted.
Relevant state bill updates for SB13, AB68, AB881, AB670 are shown in green below.


City Hint: The city permitted a total of 12 ADU project(s) in the past year of 2018, which makes it above average for ADU production compared to other cities statewide.


Number of ADUs allowed:

No more than one ADU per single-family dwelling.

AB68 & AB881 Update: Properties which convert existing space to create ADUs may be eligible for one ADU -AND- one JADU.

Types of ADUs allowed:

The ADU shall provide separate, independent accessory dwelling for one household. The ADU may be attached, detached, or located within the LIVING area of the primary dwelling unit on the lot, subject to the standards of this section. An ADU may be created within an existing single-family dwelling.

Lot size:

Per state standards.

AB68 & AB881 Update: Properties will not be subject to minimum lot standards by ordinance or of the applicable zoning district.

ADU size:

Attached ADU May was 30% of the home’s square-feet in area up to a 1,200 square-foot maximum. Detached ADU Limited to 640 square-feet maximum. Maximum floor area. The gross floor area of a detached ADU shall not exceed six hundred forty square feet. The gross floor area of an attached ADU shall not exceed thirty percent of the total living area, or the minimum area Of an efficiency unit as described in Section 17958.1 of the California Health and Safety Code, whichever is greater, with a maximum allowable floor area of one thousand two hundred (1,200) square-feet.

AB68 & AB881 Update: Properties will be allowed up to 850 square feet for a one bedroom or up to 1,000 square feet for a two bedroom ADU.


Attached ADU Must maintain the base zoning district setbacks. Detached ADU May be located in the rear one half of the lot. May be a second floor element only if located over a detached garage and meeting the base zoning district setbacks. Detached ADUs must be located a minimum of 5 feet from all sides and rear lot lines.

AB68 & AB881 Update: The maximum required setback for a detached new construction ADU shall be no more than 4 feet from the rear or side property lines.


Parking: One independently usable on-site parking space shall be provided for the ADU in addition to the parking required for the existing residence. Tandem parking is allowed to provide the minimum spaces required as long as it does not encumber access to the primary dwelling.

AB68 & AB881 Update: Properties which convert an existing garage will not be subject to replacement parking requirements.

Fire Safety:

Per state standards.

Shape, materials and style:

Architectural Compatibility. The architectural design, exterior materials and colors, roof pitch and style, type of windows, and trim details of the accessory dwelling unit shall be substantially the same as and visually compatible with the primary dwelling.
Development Standards. ADUs shall conform to the height, setbacks, lot coverage and other zoning requirements of the zoning district in which the site is located, the following development standards, other requirements of the Zoning Ordinance, and other applicable City codes. In addition to all other requirements of the zoning district, any detached accessory dwelling units shall be located a minimum of five feet from all side and rear lot lines. ADUs located above garages must conform to the setback requirement for second stories in their respective zoning districts.


The maximum height of an ADU is 15’ unless located over, a garage and then it is 28’

Design review:

Ministerial review process.

Number of Bedrooms:

Not specified by State Standards.


Owner Occupancy. Either the primary dwelling unit or the ADU shall be owner occupied. The owner must enter into a restrictive covenant with the City, recorded against the property prohibiting the rental of both units at the same time or the sale or transfer of the unit separate from the primary property.

SB13 Update: Owner-occupancy requirements for ADUs will be voided statewide for 5 years.

Utility connections:

Local health officer approval where a private sewage disposal system is being used, if required. (State requirements)

Permit Fees

SB13 Update: Local impact fees for ADUs will be reduced substantially statewide.

Existing Units

Amnesty Program: An Amnesty Program exists for preexisting units constructed prior to January 1, 2003. Please reference the Secondary Living Unit Amnesty Program handout from the Building Division:

Joint Planning and Building Division approval is required for approval through the Amnesty Program for SDUs created prior to January 1, 2003.

SB13 Update: Amnesty program to permit unpermitted units will be administered statewide, allowing non-health and safety code violations to be deferred.

Emergency Access:

Emergency Access. A SDU may be permitted only on lots with access from a roadway that meets the fire apparatus access road requirements of the California Fire Code Section 902.2.2.1.


Location. Second units may be established on any lot in any district where a primary single-unit dwelling has been
previously established or is proposed to be established in conjunction with construction of a second unit and there is no
other second dwelling unit within four hundred feet measured from nearest edge of the lot line of each respective or
proposed second dwelling unit. The Director may grant a waiver to the four-hundred-foot separation requirement if he
finds that there are no substantial parking, privacy, noise, health and safety or visual impacts to neighbors associated
with the location and siting of the detached second dwelling unit. The Director shall hold a public hearing before allowing
a waiver with notice to neighbors at least twenty days prior to the hearing and as provided for in Chapter 18.27,
Common Procedures.


Waivers: There are 3 types of Waivers that may be granted by the Director after holding a public hearing with a
notice to property owners at least 20 days prior to the hearing as required in Chapter 18.27, Common Procedures.
Waivers to standards may include: setbacks from the 5’ requirement (only for SDUs created prior to January 1, 2003)
(1) , window and door openings, or the proposed location is within 400 feet of an existing approved SDU.

Residential Building Code:

The California Building Code (CBC) 2016 without amendments is adopted.

San Carlos City Planning Offices

San Carlos Planning & Zoning

Public counter and telephone hours are 9:00 a.m. to 12:00 p.m. weekdays.

600 Elm Street San Carlos, CA 94070 San Carlos, CA 94070

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Costs / ROI


* upon completion of ADU


* based on local average price per sqft


* estimated by location


* 30 years / 5% interest rate / 20% down payment


Appreciation Estimate = (Base Value: $) / (Home's Living Space: sqft) * (ADU's Living Space: sqft)

Rental Estimate = (Rent Per Sqft: $5.63) * (ADU's Living Space: sqft)

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