ADUs, junior ADUs and SB 9 in Palo Alto

Accessory dwelling units have changed what a Palo Alto lot can hold. A backyard cottage, a converted garage or a small apartment carved out of the main house can give room to aging parents, an adult child or a renter. State law has steadily pushed cities to allow them. Since 2022 SB 9 has also let many owners build a second full house or split the lot.

This page sets out the rules as Palo Alto and the state publish them and explains the permit path. It is general information, not legal or design advice. Rules change often, so confirm details with the city's planner on duty and hire licensed professionals for design and construction. Our building permits guide covers the Development Center and inspections in general.

The kinds of units

• Detached ADU. A separate small house in the yard, often called a backyard cottage.
• Attached ADU. An addition with its own entrance, attached to the main home.
• Conversion ADU. Existing space, such as a garage or a basement, turned into a unit.
• Junior ADU (JADU). A unit of up to 500 square feet carved out of the main home. It can share a bathroom with the house but needs its own entrance and at least an efficiency kitchen.

Each has its own size, height and setback rules. The difference that matters most to many owners is occupancy. A JADU requires the owner to live in the main house or the JADU. Regular ADUs carry no owner-occupancy rule.

Palo Alto's rules as published

The city's ADU and JADU guidebook (2025) is the clearest summary. Its main numbers:

The 30-day rental minimum rules out short-term rental plans. Owners who rent an ADU take on landlord duties under state and city law, including Palo Alto's one-year lease offer rule. Our renting guide explains them.

What state law guarantees

California's ADU law sets a floor that every city must meet. The state Department of Housing and Community Development publishes a handbook and updates. The protections owners rely on most:

• Ministerial review. A complete application that meets objective standards must be approved without a public hearing, within 60 days.
• No owner-occupancy rule for regular ADUs. JADUs still require it.
• No replacement parking when a garage or carport is converted or demolished for an ADU.
• Fee limits. Impact fees cannot be charged on units under 750 square feet. Larger units can be charged in proportion to the main home's size.
• Minimum allowances. A city cannot use lot coverage or floor area rules to block a modest ADU that meets setback and height standards.

State law changes almost every year. If an older blog post or neighbor's experience conflicts with what you read here, ask the city which version applies.

SB 9: two units and lot splits

Senate Bill 9 took effect on January 1, 2022. It lets owners in single-family zones do one or both of two things with ministerial approval:

1. Build two units on one lot, for example a second full house.
2. Split the lot into two, an urban lot split. Under state law each new lot must be at least 1,200 square feet and roughly 40 percent or more of the original.

State law adds conditions. An owner splitting a lot must sign an affidavit that they intend to live in one of the units for three years. SB 9 does not apply to properties in historic districts or to listed historic properties. It also cannot be used to demolish housing that was rented in the past three years or that is rent-restricted. Short-term rentals of SB 9 units are not allowed.

How Palo Alto handles SB 9

According to the city's December 2021 SB 9 FAQ, Palo Alto adopted an interim urgency ordinance so the law could take effect locally. The city said a permanent ordinance would follow. Points from that FAQ:

• SB 9 applies in the R-1 and RE zones only.
• Local standards cannot prevent two units of at least 800 square feet each. Side and rear setbacks cannot exceed 4 feet.
• Each new parcel needs at least 15 feet of street frontage, unless that rule would block the split.
• On a lot created by an urban lot split, the city allows only two units in total, counting ADUs and JADUs.
• The city has objective design standards for SB 9 projects. A single two-story unit goes through the city's Individual Review.
• Projects in high or very high fire hazard zones are excluded unless mitigation measures are met. Flood zone sites must meet federal flood rules.

Ask a planner for the current code before you design. Our page on flood zones and insurance explains the hazard maps that can rule a site out. Owners in the Palo Alto Hills should check fire zone status first.

Fees and taxes

The 2025 guidebook gives these rough estimates. Treat them as starting points and get a quote for your project.

A new ADU counts as new construction for property tax. The Assessor adds the value of the unit to your existing assessed value without reassessing the main house. Our property taxes page explains how that works. Electric, gas, water and sewer connections run through City of Palo Alto Utilities, described in our utilities guide.

Permit steps

The city's guidebook lays out five phases.

1. Confirm eligibility. Check zoning, setbacks, easements, trees and hazard zones. Settle on the ADU type, a budget and financing.
2. Design. Hire a design professional to prepare construction drawings that follow the city's submittal format.
3. Submit and revise. Upload the plan set through the city's Accela Citizen Access portal, pay fees, answer plan check comments and receive the permit.
4. Hire a builder. Request and compare bids from licensed contractors.
5. Build and inspect. Book inspections at each stage and pass the final inspection.

Eichlers, overlays and historic homes

Many Palo Alto lots carry extra layers. Eichler tracts may sit in single-story overlay zones. Historic properties have their own review. ADU law limits how far a city can use these rules to block a modest unit, but design review, historic review and height limits can still shape what you build. SB 9 is unavailable on historic properties. Read our guide to historic home rules and talk to the historic preservation planner early if your house is on the city's inventory.

Frequently asked questions