Building an ADU in Redwood City

Redwood City now uses state ADU law

Redwood City used to have its own ADU rules in Article 37 of the Zoning Code. Ordinance 1130-892, adopted July 27, 2026, repealed Article 37. The zoning code now lists ADUs as a permitted accessory use under "Government Code Sections 66310 through 66339.5, as they may be amended from time to time."

The city's ADU handout, effective August 2026, sums up the key Planning and Building rules. It tells readers to see Government Code 66310 to 66342 for the full law. This page follows that handout. The city's ADU web page still lists some older figures (for example, a detached ADU of up to 1,000 sq ft), so confirm sizes with the Planning Division. For background on the state rules, see our California ADU law overview. [1][2][3][4]

What you can build

ADUs are allowed in all residential and mixed-use zones, "with limited exceptions, such as traffic flow, water, sewer, or public safety."

• Single-family lot: one detached ADU, one converted ADU and one junior ADU.
• Multifamily lot: up to eight detached ADUs, but no more than the number of existing units (two with a proposed multifamily building), plus conversions of non-living space for up to 25% of the existing units.
• JADUs: only inside single-family homes on lots zoned R-1 or RH, one per lot.

Every ADU must have a real kitchen. The city says that means "a stove/oven, 2-20 amp circuits, a sink and a food preserving appliance." Wet bars with countertop ovens don't count. The ADU's main entrance must be a side-hinged door, not a garage or patio door. [3][4]

Size, height and setbacks

Per the city's August 2026 handout:

• Minimum size: 150 sq ft.
• Detached ADU: up to 850 sq ft for a studio or one bedroom, and up to 1,200 sq ft for two or more bedrooms.
• Attached ADU: up to 50% of the existing home.
• Height: an attached ADU can reach the zone's height limit. A detached ADU within a half mile of a major transit stop can be 18 feet, plus 2 more feet for roof pitch. ADUs on multifamily lots can be 18 feet. All others can be 16 feet.
• Setbacks: 4 feet from side and rear lot lines for new construction. A converted structure keeps its existing setbacks.

Lot coverage, pervious area, open space and accessory structure rules of your zone still apply. But the city says "these restrictions cannot prevent you from building an 800 square foot ADU."

HCD, the state housing agency, says that where a city doesn't have its own compliant ADU ordinance, state law caps a new detached ADU at 1,200 sq ft and an attached ADU at 50% of the main home (at least 800 sq ft). The handout's 850 sq ft limit for a detached studio or one-bedroom ADU is lower than that 1,200 sq ft figure, and the city's ADU web page lists still other numbers (850 sq ft for one bedroom and 1,000 sq ft for more). The sources don't agree, so confirm the size limit with the Planning Division before you design. [3][4][5]

Parking

Redwood City requires no new off-street parking for an ADU or JADU. The city's ADU page says "no additional parking is required" for a detached ADU in single-family areas. State law also says a city can't require you to replace a garage or carport you convert or tear down to build an ADU. [3][4][5]

Fees

The city publishes these base fee estimates for a new ADU:

• Up to 400 sq ft, or converting an existing garage: $3,999.53
• 401 to 600 sq ft: $4,660.62
• 601 to 800 sq ft: $5,321.71

The city says these are estimates and "additional fees will be applied based on construction valuation," plus administrative, maintenance and other fees. See the city's Master Fee Schedule for all fees. A new address also carries an address fee, and fire flow requests have a fee.

The city says it charges no impact fees on ADUs under 750 sq ft. State law sets the cutoff at 750 sq ft or less, with proportional fees above that. The city must report each ADU to the school district, which decides on its own whether to charge school impact fees. HCD says school districts may charge fees on ADUs larger than 500 sq ft. For cost ranges, see our ADU cost guide. [3][4][5][6]

Fire safety and the fire flow test

For a new detached ADU, you need a fire flow test with your permit application to show there is enough water for firefighting. Request it through the city's Fire Flow Information Request page. The city says to allow about 20 business days, and that reports "may take up to 6 weeks." Start early.

Other fire and building rules from the handout and checklist:

• Fire sprinklers may be needed if the house already has them, or if an attached ADU addition plus any major remodel equals 50% of the main living area or 1,000 sq ft, whichever is less. JADUs are exempt.
• The city says there should be a one-hour fire separation between the ADU and the main house.
• Smoke detectors must be interconnected, and carbon monoxide alarms are required.
• Your site plan must show a hose-pull route showing every part of the ADU's exterior is within 150 feet of where a fire engine parks.
• In a FEMA flood hazard area, the ADU's lowest floor must be above the base flood elevation.

[3][4][6][7]

Garage conversions and junior ADUs

Converting a garage is one of the most common ADU routes. A converted structure keeps its existing setbacks, and the city's lowest base fee estimate applies to a garage conversion. A garage door can't serve as the ADU's main entrance, and the replacement wall must match the house in color and materials. See our garage conversion guide.

A junior ADU can be up to 500 sq ft, inside a single-family home on an R-1 or RH lot. You may add up to 150 sq ft for an entrance. A JADU can share a bathroom with the main home; if it does, it needs inside access to the house and the owner must live in the JADU or the main home. [3][4]

Renting and the ADU survey

Owner occupancy is not required for an ADU. Short-term rentals of less than 30 days are prohibited for ADUs and JADUs.

Before the city will final your building permit, you must complete a short ADU Homeowner Survey about how the unit will be used and its expected rent. Send the email confirmation to the Building Department at permits@redwoodcity.org. [3][4]

Lot splits and duplexes (SB 9)

Redwood City applies SB 9 in its single-family zones through Zoning Code Section 5.10. On a lot that hasn't been split, you can build an SB 9 project and also apply for ADUs. On a lot created by an urban lot split, you can have up to two units in total, counting ADUs and JADUs. SB 9 homes need 4-foot side and rear setbacks and follow the zone's height limit. An SB 9 project can't demolish or alter housing rented by a tenant in the last three years, and it isn't allowed on some sites, such as historic properties and certain hazard areas. See our SB 9 lot split guide. [8]

Permit steps in Redwood City

1. Get early advice

   Book a Zoom appointment with Planning staff through the city's online booking page, or call (650) 780-7234. The San Mateo County ADU Resource Center also offers one-on-one feasibility consults. [4]

2. Request a fire flow test early (new detached ADUs)

   Submit a request through the city's Fire Flow Information Request page. Reports can take up to six weeks. [4][6]

3. Prepare plans or choose pre-reviewed plans

   Hire a designer, or use free HEART GLADUR plans that the city has pre-reviewed. Pre-reviewed plans still need a site plan, foundation and utility details for your lot. [4]

4. Complete the ADU Completeness Checklist

   Fill out the ADU Completeness Checklist. ADUs need their own application, plan set and permit number. The city says incomplete applications "will not be accepted and will not be subject to State shot clock guidelines." State law still requires the city to tell you within 15 business days whether your application is complete. [5][7]

5. Apply online through eTrakIt

   Upload your plans, building permit application and checklist on eTrakIt. [4]

6. Get an address and build

   The ADU needs its own address (the checklist says before the rough framing inspection) and an address fee applies. Projects valued over $50,000 must file a construction and demolition recycling form. [3][4][7]

7. Complete the ADU survey and final the permit

   Complete the ADU Homeowner Survey and email the confirmation to permits@redwoodcity.org to finalize the building permit. [4]

Pre-approved and sample plans

• Pre-Reviewed ADU Plans

  Designers submit model plans for city pre-review; using one cuts the city's review timeline to 30 days, though you still need site-specific plans. [4]

• HEART GLADUR free ADU plans

  Free, all-electric detached ADU plans (studio 400 sq ft, one bedroom 575 or 745 sq ft, two bedrooms 800 sq ft) pre-reviewed by the city; a user agreement is required. [4]

Who to call

• Planning Division

  ADU zoning rules, appointments and pre-reviewed plans (planning@redwoodcity.org)

  650.780.7234

  1017 Middlefield Road, Redwood City, CA 94063

  [3][4]

• Building Division (permits)

  Building permit submittals and ADU survey confirmations (permits@redwoodcity.org)

  [4]

• Engineering, Fire Flow requests

  Fire flow information for permits (FireFlow@redwoodcity.org)

  [6]

Questions people ask