San Carlos Accessory Dwelling Unit (ADU) Standards

        New laws were recently passed, and updates will be coming soon


Brittany Whitehill, Planning Technician

650-802-4208 – This email address is being protected from spambots. You need JavaScript enabled to view it.


ADU Ordinance



Zones allowed

RS-3, RS-6, RM-20 and RM-59

Lot restrictions

RS-3 maximum lot coverage is 25-35%.
RS-6 maximum lot coverage is 50%.
RM-20 maximum lot coverage is 65%.
RM-59 maximum lot coverage is 75%.
Must contain a previously established single-family dwelling.

Minimum lot size


Min / Max ADU size

State law provisions apply as follows:

  • Max detached: 1,200 sf
  • Max attached: 50% of living space
ADU building height

Attached to main residence: 28 feet

Above detached garage: 28 feet

All other: 12-15 feet


Above garage: 5 feet sides and rear
RS-3, attached to main residence: first story side setback 10 feet; second story side setback 14 feet; rear setback 20 feet
RS-6, attached to main residence: first story side setback 5 feet; second story side setback 9 feet; rear setback 15 feet

Parking requirements
One space is required unless state exemptions are met (ADU is within 1⁄2 mile of transit, in existing structures, in historic districts, within one block of car share locations, or in an area with residential parking permit rules that do not allow second units to get a permit). Parking in setbacks is allowed, and tandem parking is allowed if it does not encumber access to the required parking for the single-family dwelling. All other ADUs may be granted a parking waiver, subject to public hearing.
Owner occupancy

Owner must live in the main dwelling or the ADU

Sample fees from recently built projects*

ADU (500 sf, garage conversion): $3,000

Other requirements
  • ADUs must conform to all development standards in the Zoning District in which they are proposed. An ADU must comply with minimum requirements as listed in Government Code Section 65852.2 (a)(3)(b)(1)(a)(A, B, C, D, E, F, G, H, and I).

  • The architectural design, exterior materials and colors, roof pitch and style, type of windows, and trim details of the second dwelling unit shall be substantially the same as and visually compatible with the primary dwelling.

  • A permit may be required for tree removals.

  • Only one ADU per property is allowed.

Applicants may submit to the Building Division for building permits. Once received by Building, plans are routed to planning for review and informal approval. Applicants are encouraged to meet with Planning before submitting plans to Building.
Waivers may be granted for some of the ADU development standards, but are subject to public hearing. The Director may grant a waiver to the 400 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.
Disclaimer: standards and process may vary. Consultation with the contact is recommended before starting any project. This summary was prepared by 21 Elements, not the City of San Carlos.

*Fees are specific to each project and will vary. Fees change regularly. These are provided as examples only.

Download ADU Standards PDF

Updated: 12/11/2017