Two Detached ADUs in San Bruno (AB 956, 2027)
Plan Two ADUs in San Bruno: Free Site Assessment
San Bruno ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires cities, including San Bruno, to approve up to two detached ADUs on a lot with a single-family home. San Bruno has already simplified its process: ADUs now go straight to a building permit, with no separate Planning step. Here is how the new law and the city’s current rules fit together.
- Units allowed now: the city’s ADU code (Municipal Code Chapter 12.90, last amended by Ordinance 1965 in August 2025) allows one ADU on a lot with a single-family home, plus one JADU inside the house.
- Size: the code allows 850 sq ft for a studio or one-bedroom ADU. Two or more bedrooms can reach 1,000 sq ft on lots under 7,500 sq ft, or 1,200 sq ft on larger lots. A JADU can be up to 500 sq ft.
- Height: 16 ft for a detached ADU on a single-family lot, plus 2 ft to match the roof pitch. Up to 25 ft is allowed for an ADU over a legal detached garage.
- Setbacks: 4 ft side and rear. The code sets no minimum separation from the main house, but building and fire codes still apply.
- Parking: one space per ADU unless exempt, for example within a half mile of transit. A garage conversion does not need replacement parking.
- Process: apply for a building permit through MGO Connect. Plans route to Building, Fire, Planning and Public Works. The first review takes about 3 to 4 weeks and each later review about 1 to 2 weeks.
- Pre-approved plans: San Bruno runs an AB 1332 pre-approved ADU program and posts approved plans with designer contacts.
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.
San Bruno’s code allows one ADU per single-family lot, so it will need to update Chapter 12.90 to allow two detached units. The city’s current 850 to 1,200 sq ft limits are above the 800 sq ft cap the law allows for each unit, so the city may set a lower size for two-unit projects. Its 16 ft detached height can stay. We will confirm how the city writes these changes as it updates its code.
Recent Axiom work
Professional photos from a recent Axiom Renovation full remodel and addition in Los Gatos.
Planning two detached ADUs on a San Bruno lot
- Survey: the city requires a boundary survey when an ADU sits within 3 inches of the required setback. With two units on one lot, that is common.
- Fire flow: the water supply must meet Fire Code fire-flow standards. We check this early for each unit.
- Sprinklers: the code does not require sprinklers in an ADU if the main house does not need them.
- Utilities: separate gas and electric meters apply unless an exemption fits. Two ADUs usually need a load calculation and often a service upgrade.
- Rentals: ADUs permitted after 2020 cannot be rented for less than 30 days.
Building ADUs in San Bruno with Axiom
We design, permit and build ADUs across the Peninsula. Read our San Bruno ADU builder page, see our San Bruno service area, or start with the AB 956 overview. Next door, see the guide for Millbrae.
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 Bruno Two-ADU FAQ
Can I build two detached ADUs in San Bruno?
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. Until then, San Bruno’s code allows one ADU and one JADU.
How large can each ADU be in San Bruno?
Today the city’s code allows 850 sq ft for a studio or one-bedroom ADU and up to 1,000 or 1,200 sq ft with two or more bedrooms, depending on lot size. Under AB 956, the city may limit each of two detached ADUs to 800 sq ft.
How tall can a detached ADU be in San Bruno?
The code sets 16 ft for a detached ADU on a single-family lot, plus 2 ft to match the roof pitch. An ADU over a legal detached garage can reach 25 ft.
How long does an ADU permit take in San Bruno?
The city says the first plan review takes about 3 to 4 weeks and each later review about 1 to 2 weeks. You apply directly for a building permit through MGO Connect.
Do I need a survey for an ADU in San Bruno?
Yes, when the ADU is within 3 inches of the required setback, the city requires a boundary survey. Two units placed near 4 ft side and rear setbacks often need one.
Who builds two-ADU projects in San Bruno?
Axiom Renovation designs, permits and builds ADUs in San Bruno 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.