Two Detached ADUs in Palo Alto (AB 956, 2027)
Plan Two ADUs in Palo Alto: Free Site Assessment
Palo Alto ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires the City of Palo Alto to approve up to two detached ADUs on a lot with a single-family home. Palo Alto has some of the region’s most detailed protected-tree rules, which shape where backyard units can go. Here is how the new law and the city’s current ADU rules fit together.
Palo Alto’s ADU rules are in Municipal Code Chapter 18.09, most recently amended by Ord. 5656 in 2025.
- Units allowed now: the city’s ADU code allows one attached ADU, one detached ADU and one JADU under its state-standard table, or one ADU plus one JADU under local standards.
- Size: a state-standard detached new unit may be 150 to 800 sq ft. Local-standards units may be 900 sq ft, or 1,000 sq ft with two or more bedrooms. A JADU may be up to 500 sq ft.
- Height: 16 ft for a state-standard detached unit, or 18 ft within a half mile of transit, plus 2 ft for a matching roof pitch.
- Setbacks: 4 ft side and rear.
- Separation: at least 3 ft between a detached unit and the main house, wall to wall.
- Parking: none required for the ADU, and no replacement parking.
- Process: ministerial building permit, decided within 60 days or deemed approved.
State review of Palo Alto's ADU rules
The state housing department (HCD) reviewed Palo Alto’s ordinance several times. In December 2022 it flagged daylight-plane and parking issues. In October 2024 it found the city’s 2023 ordinance out of compliance, citing a 16 ft height cap near transit, a one-ADU-plus-JADU limit and tree rules that could delay ADUs. 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 requires the city to approve up to two detached new-construction ADUs on a single-family lot. The city may cap each at 800 sq ft of living space and apply height limits; side and rear setbacks can be no more than 4 ft. Where two detached ADUs are built, a JADU need not be approved, and HOA rules cannot block or unreasonably restrict the units. Palo Alto’s state-standard detached unit already tops out at 800 sq ft, so that size carries over. The change is the count. One detail matters for two units: the code exempts up to 800 sq ft of ADU area from floor area and lot coverage, shared between the ADUs on the lot. The city will need to update Chapter 18.09, and we confirm current rules as it does.
Planning two detached ADUs on a Palo Alto lot
- Protected trees: native oaks, bigleaf maple and incense cedar of 11.5 inches or more, coast redwoods of 18 inches or more and other trees of 15 inches or more are protected. Each has a protection zone of 10 times its trunk diameter. Tree rules cannot delay or deny the permit.
- Second-story privacy: no second-story doors or decks facing an interior lot line, and 5 ft sills or opaque glass on windows facing those lines.
- Flood zones: units in a flood zone do not get the height extension.
- Sprinklers: an ADU needs sprinklers only if the main house requires them.
- Electrical: two units usually need a load calculation and often a service upgrade.
Building ADUs in Palo Alto with Axiom
See our Palo Alto ADU guide and Palo Alto service area, read the AB 956 overview, or compare neighboring Menlo Park and Mountain View.
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.
Palo Alto Two-ADU FAQ
Can I build two detached ADUs in Palo Alto?
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, the city’s code allows one detached ADU, one attached ADU and one JADU.
How large can each ADU be in Palo Alto?
A state-standard detached unit can be 150 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 Palo Alto?
16 ft under the state-standard rules, or 18 ft within a half mile of transit, plus 2 ft for a matching roof pitch. Flood-zone lots do not get the extension.
How far must a detached ADU be from the house in Palo Alto?
At least 3 ft, wall to wall. Side and rear setbacks are 4 ft.
Will protected trees stop my Palo Alto ADU?
Tree rules cannot delay or deny an ADU permit, but they shape the design. Protection zones are 10 times the trunk diameter, and replacement trees may be required.
Who builds two-ADU projects in Palo Alto?
Axiom Renovation designs, permits and builds ADUs in Palo Alto 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.