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(650) 730-2387 ext: 501
Schedule ADU Consultation (650) 730-2387 ext: 501

San Carlos ADUs

Everything about building Accessory Dwelling Units in San Carlos, CA

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San Carlos ADU Guidelines Last Updated 10/13/20

The city government of San Carlos will approve ADUs under California's statewide mandated regulations.
The California Building Code (CBC) 2019 is adopted.


City Hint: The city permitted a total of 14 ADU projects in the past year of 2019, which makes it above average for ADU production compared to other cities statewide.

Number of ADUs allowed:

-One ADU and one JADU is allowed per single-family lot.
-Up to two detached ADUs are allowed on a lot with an existing multi-family structure.
-Up to 25% of the existing units in a multi-family structure are allowed in portions of the

Types of ADUs allowed:

Detached ADU, Attached ADU, Junior ADU are allowed. Accessory Dwelling Units may be new construction or converted from existing space. Junior Accessory Dwelling Units must be converted from existing space.

Lot size:

ADU projects on single family or multi-family residential lots will not be subject to the minimum lot size of the underlying local zoning code or by special ordinance. ~ AB68 & AB881 Update

ADU size:

Per State law, a studio or one-bedroom ADU is limited to a maximum of 850 square feet; and an ADU with two-bedrooms or more is limited to a maximum size of 1,000 square feet.

ADU may be larger than 800 sq. ft. when compliant with City’s MFA and Lot Coverage requirements. (850 1-bdrm; 1,000 2+bdrms). In this scenario, the property owner would not be allowed to increase the primary house at a later date because MFA is maxed out.


Yes. ADUs can now be four feet away from a side or rear setback (was previously five feet). (Note: since JADUs occur within an existing primary residence, they must meet/adhere to the setbacks of the primary residence.)


Properties which convert an existing garage to an Accessory Dwelling Unit or Junior Accessort Dwelling Unit (JADU) will not be subject to replacement parking requirements. ~ AB-68

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 a detached ADU is 16 feet per State law. If the ADU is above a garage, the State allows each city to determine the maximum height. To manage massing, bulk, and privacy, the Planning Commission’s recommendation is a maximum of 20 feet for an ADU over a garage. (Note: the front yard 2nd story setback of 19 feet in the RS-6 District would still apply to ADUs proposed over garages located in the front portion of the lot).

Design review:

Ministerial review process.

Number of Bedrooms:

Not specified by State Standards.


The most recent new law states that cities cannot require the owner to occupy either the primary residence or the ADU. This means that both the primary residence and the ADU do not have to be owner occupied. This law may change on January 1, 2025. (Note: owner occupancy is still required for scenarios where a JADU is provided within the primary residence.)

Utility connections:

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

Allowed Zones:

*** Beginning in 2020, according to state law, all residential zoning districts, including single-family and multi-family, are allowed to build Accessory Dwelling Units. ***

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.

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) 2019 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

Call/Text ADU Operator (650) 730-2387
Dial Ext: 501
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ADU Design Library

Browse hundreds of models to find the right fit for your property.

ADU Model 400 sqft

W 20 ft L 20 ft

ADU Model 700 sqft

W 35 ft L 20 ft

ADU Model 484 sqft

W 22 ft L 22 ft

Customer Reviews

"Housable has been a great resource regarding my ADU project. I purchased both the Property and Design Reports. In both cases, they delivered as promised and on time."

Ed in Corona, CA

"My experience with Housable was exceptional. The team was extremely helpful and responsive. I am very satisfied and happy to have used these services. As a home owner I do not know the construction lingo or process but the Housable team very kind and helpful and patient with me. My expectations were exceeded. Thank you for everything."

Monica H. in Oakland, CA

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Alexandria in Santa Ana, CA

Complete 5-Step Process

Browse hundreds of permit-ready ADU designs and order one to customize to your needs.
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Select your contractor and build your project.

What our customers say:

Customer Reviews

"My permits were APPROVED, thank you for all your hard work. I am in the process of meeting with contractors. "

Mary S. in San Jose, CA

"I just wanted to let you know that the permit process has been completed and we are currently in the construction phase. The work you guys did was great and I will definitely be using this service again in the future. I will keep you guys updated on anything important. Thanks!"

Patrick L. in Orange County, CA

Detached ADU - Completed in 2020
1,003 sq. ft., 3 bed, 2 bath

Estimate Your ADU Potential
Costs / ROI



* upon completion of ADU


* based on local average price per sqft


* estimated by location


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


Size: 500 sqft


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)

Check your property's zoning, browse designs & get contractor estimates for your ADU project:

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