Two Detached ADUs in San Carlos (AB 956, 2027)
Plan Two ADUs in San Carlos: Free Site Assessment
San Carlos ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires cities, including San Carlos, to approve up to two detached ADUs on a lot with a single-family home. San Carlos is already rewriting its ADU ordinance, with a Planning & Transportation Commission hearing set for November 16, 2026. Here is how the new law and the city’s current rules fit together.
- Code: Municipal Code §18.23.210, adopted as Ordinance 1604 on November 13, 2023.
- Units allowed now: one ADU and one JADU under the current ordinance. HCD has told the city it must allow a conversion ADU, a detached ADU and a JADU, plus one more qualifying unit.
- Size: a state-exempt ADU can be up to 800 sq ft. A JADU can be up to 500 sq ft, inside the home, in RS districts only.
- Height: 16 ft, or 18 ft near transit or when the main house has more than one story. An attached ADU can be 25 ft or the zoning limit. ADUs can also go over or under a legal detached garage.
- Setbacks: 4 ft side and rear.
- Process: ministerial, with no hearing. Plans go to the Building Department.
- Pre-approved plans: under AB 1332, designers submit plans marked “Pre-Approved ADU.” Homeowners can browse a free online gallery, but plans are copyrighted, so the designer’s permission is needed.
State review of San Carlos's ADU rules
On May 6, 2026, the state housing department (HCD) sent San Carlos a letter with 37 findings on Ordinance 1604. HCD asked the city to add recent state laws, measure the 800 sq ft as living space, remove ADU owner occupancy, remove front setbacks and lot coverage for ADUs of 800 sq ft or less, add the new-home parking exemption, and fix inconsistent height values. Where local rules are stricter than state law, state law applies.
Recent Axiom work
Professional photos from a recent Axiom Renovation full remodel and addition in Los Gatos.
What changes on January 1, 2027
AB 956 raises the number of detached ADUs the city must approve on a single-family lot to two, both new construction. The city may limit each of the two to 800 sq ft of living space and apply its height limits, and side and rear setbacks can be no more than 4 ft. Where two detached ADUs are built, the city does not have to approve a JADU on the same lot. The law also limits how homeowners associations can restrict these units.
The city’s 2026 ordinance update is the natural place to add the two-unit option, though we did not find AB 956 in its materials yet. The city’s 800 sq ft state-exempt ADU already matches the cap allowed for each unit. We will review the November draft and confirm the final rules as the city adopts them.
Planning two detached ADUs on a San Carlos lot
- Zoning and overlays: overlay districts can limit changes to pre-approved plans. We check the city’s zoning map for each lot first.
- Units over garages: the code allows an ADU over a legal detached garage. HCD flagged the height values, so we confirm the limit before design.
- Electrical: two ADUs usually need a load calculation and often a service upgrade.
- Rentals: ADUs need a 30-day minimum rental and cannot be sold separately. ADUs have no owner occupancy or deed restriction; JADUs record one.
Building ADUs in San Carlos with Axiom
See our San Carlos ADU builder page and San Carlos service area, or read the AB 956 overview. Nearby, see the guides for Belmont and Redwood City.
Process
Our ADU Process
Step 1
Initial Consultation
We begin with a thorough initial consultation to understand your needs, assess your space, and discuss your vision, budget, and timeline.
Step 2
Planning and Design
At Axiom Renovation, we understand that the planning and design phase of an ADU project is crucial to its success. Our dedicated project managers will work closely with you to understand your goals, design ideas and budget for the project.
Step 3
Material Selection
We guide you through selecting high-quality materials that fit your design and budget, ensuring durability and aesthetic appeal.
Step 4
Demolition and Preparation
Careful demolition and preparation work are performed to ready the space for construction, minimizing disruptions and ensuring a clean work environment.
Step 5
Construction and Installation
Our skilled craftsmen handle the construction phase, including obtaining permits, scheduling appointments, and the actual construction and installation with precision, building the new space according to the approved design.
Step 6
Electrical and Plumbing Work
Licensed professionals conduct all electrical and plumbing work, ensuring everything is up to code and seamlessly integrated into the new ADU.
Step 7
Painting and Finishing
We pay close attention to detail during the painting and finishing stage, ensuring all surfaces are properly prepared and beautifully finished.
Step 8
Fixture and Appliance Installation
We expertly install all fixtures and appliances, ensuring they function correctly and fit perfectly with the overall design.
Step 9
Final Touches and Clean-Up
Final touches are added, and a thorough clean-up is performed, leaving your new space pristine and ready for use.
Step 10
Final Walkthrough and Client Satisfaction
We conduct a final walkthrough with you to ensure every detail meets your expectations and address any remaining concerns, ensuring your complete satisfaction.
San Carlos Two-ADU FAQ
Can I build two detached ADUs in San Carlos?
From January 1, 2027, AB 956 requires the city to approve up to two detached, new-construction ADUs on a lot with a single-family home, if the project meets objective standards. The city is updating its ADU ordinance now.
How large can each ADU be in San Carlos?
San Carlos allows a state-exempt ADU of up to 800 sq ft today. Under AB 956, the city may limit each of two detached ADUs to 800 sq ft of living space.
How tall can a detached ADU be in San Carlos?
16 ft, or 18 ft near transit or when the main house has more than one story. HCD flagged inconsistent height values, so we confirm limits with the city.
Does San Carlos have pre-approved ADU plans?
Yes. Designers can submit AB 1332 pre-approved plans, and homeowners can browse a free online gallery. You need the designer’s permission to use a plan.
When is San Carlos updating its ADU rules?
A Planning and Transportation Commission hearing on the 2026 ADU ordinance update is scheduled for November 16, 2026.
Who builds two-ADU projects in San Carlos?
Axiom Renovation designs, permits and builds ADUs in San Carlos and is planning two-unit projects for 2027. Call 408-702-2022, Monday to Friday, 9 am to 5 pm.
Sources: AB 956 (Quirk-Silva), signed September 29, 2026, effective January 1, 2027, as summarized by Brownstein Hyatt Farber Schreck and California YIMBY. This page is general information, not legal advice. Local rules change; we confirm current requirements with the city for every project.