Redwood City / ADU construction
ADU Construction in Redwood City
Redwood City allows a detached ADU up to 1,200 square feet. Start with the fire flow test.
Most Redwood City lots can add a detached ADU, a conversion ADU and a junior ADU with a building permit alone. We design and build ADUs here from the site check to final, with the fire flow request and the eTRAKiT submittal started before the plans are finished.
REDWOOD CITY AT A GLANCE
Who handles a Redwood City ADU.
Planning sets the size and setback rules, the Building Division issues the permit through eTRAKiT, and the city's own water utility runs the fire flow test. Each step has its own queue, so we start them together.
- 62%
- of Redwood City homes built before 1980
- 1,200
- square feet maximum for a detached ADU with 2 or more bedrooms
- 30
- days of permit review for a city pre-reviewed ADU plan
Permits
Building & Code Enforcement
Plans, the permit application and the ADU Completeness Checklist are submitted online through eTRAKiT. Questions go to permits@redwoodcity.org; the city notes replies can take up to 3 days during high volume.
(650) 780-7350ADU permit page ↗Planning
ADU rules and Zoom appointments
The Planning Division answers zoning questions and books online Zoom appointments. The San Mateo County ADU Resource Center at smcadu.org offers free one-on-one feasibility consults for Redwood City owners.
(650) 780-7234ADU handout, August 2026 ↗Water
Redwood City Water fire flow
Every new detached ADU needs a fire flow report. The city asks for about 20 business days and warns that reports may take up to 6 weeks; a fee applies. Requests go to FireFlow@redwoodcity.org.
Fire flow request ↗Utilities
PG&E plus WestLight Energy
PG&E delivers power and gas; WestLight Energy, the new name of Peninsula Clean Energy since July 2026, supplies the electricity. WestLight's appliance rebates exclude new construction, including ADUs, so an ADU budget should not count on them.
WestLight appliance rebates ↗REDWOOD CITY ADU TYPES
Bedroom count sets the size.
Under Redwood City's ADU handout effective August 2026, a detached ADU can reach 850 square feet as a studio or one-bedroom and 1,200 square feet with two or more bedrooms. An attached ADU is limited to 50 percent of the existing home. Height is 16 feet in most locations, and 18 feet plus 2 feet for roof pitch within half a mile of a major transit stop.
Detached ADU
850 square feet for a studio or one-bedroom, 1,200 for two or more bedrooms, with 4 foot side and rear setbacks. New detached ADUs must be all-electric under the city's reach code.
Attached ADU
Up to 50 percent of the existing home and the height allowed by the zoning district. Fire sprinklers can be triggered when the ADU plus remodeling reaches 50 percent of the home or 1,000 square feet.
Garage conversion
Keeps the existing setbacks. Needs a one-hour separation from the main house and a side-hinged entry door, since a garage or patio door cannot be the main entrance.
Junior ADU
Up to 500 square feet inside a single-family home on an R-1 or RH lot, plus up to 150 square feet for an entrance. The owner must live on site if the bathroom is shared.
Pre-reviewed plans
City pre-reviewed designs cut permit review to 30 days. HEART's free GLADUR plans for all-electric ADUs of 400 to 800 square feet are pre-reviewed for Redwood City.
Multifamily lots
Up to eight detached ADUs, not more than the number of existing units, plus conversion of non-living space for up to 25 percent of the existing units.
ADU HANDOUT, AUGUST 2026
Detached, attached or junior.
Redwood City follows the state ADU law in Government Code 66310 to 66342 and publishes its own summary of the limits. Here is how the three main types compare.
| Detached ADU | Attached ADU | Junior ADU | |
|---|---|---|---|
| Maximum size | 850 sq ft studio or 1-bed, 1,200 sq ft 2+ beds | 50% of the existing home | 500 sq ft, plus 150 sq ft for an entrance |
| Height | 16 ft, or 18 ft plus 2 ft near major transit | Up to the zoning district limit | Within the existing home |
| Side and rear setbacks | 4 ft | 4 ft | Same as the home |
| Where allowed | All residential and mixed-use zones | All residential and mixed-use zones | Single-family homes in R-1 and RH zones |
| Owner occupancy | Not required | Not required | Required if the bathroom is shared |
| Parking | Not required | Not required | Not required |
BEFORE YOU APPLY
What Redwood City asks for.
Documents to gather
- Site plan with distances to every property line and the water, sewer, gas and electric connections
- Floor, roof and elevation plans with the CALGreen checklist
- Structural plans and calculations, including seismic bracing
- Title 24 energy calculations and forms
- Fire flow report requested through Engineering
A pre-reviewed plan fits when
- The design is from the city's pre-review program or HEART's GLADUR set
- A designer adds the site plan, foundation and utility plans
- The lot meets zoning and site conditions for that footprint
- School district fees are budgeted, since they still apply
Expect a longer path when
- The main house already has fire sprinklers
- The lot is in a FEMA flood hazard area and the floor must be raised
- The home is in a Redwood Shores HOA that must approve plans first
- An attached ADU comes with a large remodel of the house
Planning the work
How a Redwood City ADU gets built.
Site check
Free visit. Lot, setbacks, zoning, flood zone, existing fire sprinklers and the routes for water, sewer and power.
Fire flow and design
Fire flow request filed with Redwood City Water on day one, then custom plans or a pre-reviewed plan adapted to the site.
Permit
Plans and the ADU Completeness Checklist uploaded to eTRAKiT. ADUs are excluded from One-Stop review, so full plan check is scheduled in.
Build and final
Foundation, framing, rough-in inspections requested online, finishes, the new address assigned, then final inspection.
WHAT SLOWS ADUS IN REDWOOD CITY
Problems Redwood City owners run into, and how we plan around them.
From Redwood City's own ADU, fire flow and permit pages and local news coverage. Most delays sit outside the building itself.
The fire flow report takes weeks and holds up the permit.
The request goes to Redwood City Water at the start of design, since the city warns reports can take up to 6 weeks.
Permit questions by email wait days for an answer.
Submittals are complete and every file is named with the address, as the city requires, which avoids rejected uploads and extra rounds of email.
Redwood Shores HOA rules force plan changes after city review.
We get the owners association's stamped approval first; the city recommends submitting it with the plans to avoid revision fees.
Existing sprinklers in the main house bring sprinklers into the ADU.
Sprinklers and the 50 percent or 1,000 square foot rule are checked before the layout is fixed.
The lot sits in a FEMA flood hazard area.
The flood map is checked at the site visit, since the ADU's lowest floor must sit above base flood elevation.
FEMA has told the city the Redwood Shores levee no longer meets its accreditation standards.
For Shores lots we confirm the current flood zone and the status of the levee project the council approved in February 2026 before setting floor heights.
Sources: redwoodcity.org ADU handout, fire flow and owners association pages; Redwood City Pulse, February 10, 2026.
How big can an ADU be in Redwood City?
Up to 1,200 square feet for a detached ADU with two or more bedrooms and 850 square feet for a studio or one-bedroom, under the city's ADU handout effective August 2026. An attached ADU is capped at 50 percent of the existing home, a junior ADU at 500 square feet, and any ADU must be at least 150 square feet.
What are the ADU permit fees in Redwood City?
Base fees are $3,999.53 for an ADU up to 400 square feet or a garage conversion, $4,660.62 for 401 to 600 square feet and $5,321.71 for 601 to 800 square feet, according to the city's ADU page. Valuation-based, administrative and fire flow fees are added, and school district fees still apply.
Does a new ADU in Redwood City have to be all-electric?
Yes, for a new detached ADU. Redwood City's ADU permit checklist states that under the city's reach codes all new detached ADUs must be all-electric, so the heat pump, water heater, cooking and laundry circuits are designed in from the start.
How long does a fire flow test take for an ADU in Redwood City?
About 20 business days, and up to 6 weeks during heavy demand, according to the city's fire flow page updated in February 2025. A fire flow report is required for every new detached ADU, to confirm water supply and size fire sprinklers if they are needed, and a fee applies.
Does an ADU in Redwood City need parking or fire sprinklers?
No parking is required for an ADU or junior ADU. Fire sprinklers may be required if the main house already has them, or if an attached ADU plus substantial remodeling equals 50 percent of the main living area or 1,000 square feet, whichever is less. Junior ADUs are exempt.
Can I rent out an ADU in Redwood City?
Yes, for stays of 30 days or longer. Rentals under 30 days are prohibited for ADUs and junior ADUs. Owner occupancy is not required for an ADU, only for a junior ADU that shares bathroom facilities with the main home.
