ADUs and garage conversions Redwood City

What it takes to add an ADU in Redwood City, from the Shores to the hills

Redwood City's ADU handout, effective August 2026, sets the frame: a detached unit of up to 850 square feet with one bedroom or 1,200 with two or more, 16 feet tall on most lots, 4 feet from side and rear lines. A newly built detached ADU then needs two things a conversion does not: a fire flow test to prove the water supply, and a geotechnical soils report, which counts for most on bay mud and hillside lots.

Detached ADU size
850 sq ft for a studio or 1-bed; 1,200 sq ft for 2+ bedrooms
Height on most lots
16 ft; 18 ft plus 2 for roof pitch near a major transit stop
Pre-reviewed plans
City review in 30 days; HEART offers four free all-electric designs
Before the final
A short ADU Homeowner Survey, required to close the permit
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  • Rules on this page checked against 10 public sources, October 2026
Redwood City's City Hall
Redwood City's City Hall. Photo: King of Hearts, CC BY-SA 4.0, via Wikimedia Commons.

Permits and local rules

Redwood City steps that can hold up an ADU permit

  1. The fire flow test

    For a new detached ADU, Redwood City wants a fire flow test with the permit submittal, both to show the water available at the site and to size fire sprinklers if they turn out to be needed. On land served by Redwood City Water, Engineering takes the request online, may answer from a hydraulic model or a physical test, and charges a fee. The checklist asks for at least 1,000 gallons per minute with 20 psi left at residual pressure, the distance to the nearest hydrant, and a hose-pull diagram keeping every side of the ADU within 150 feet of where the engine parks.

    City of Redwood City, ADU Completeness Checklist (opens in a new tab)

  2. Soils, trees, surveys and the Hetch Hetchy strip

    The checklist requires a geotechnical soils report for every newly built detached ADU and may ask for one on an attached unit, depending on the site. Removing a tree 12 inches in diameter or more takes a tree removal permit, a structure within 4 feet of a property line needs a survey, and Class B is the minimum roof rating. A lot next to the San Francisco Public Utilities Commission's Hetch Hetchy right-of-way must notify the SFPUC before submitting, because no structures or construction staging are allowed on that land.

    City of Redwood City, ADU Completeness Checklist (opens in a new tab)

  3. What counts as a kitchen, and an address of its own

    To qualify as an ADU, the unit's kitchen needs a stove or oven, two 20-amp circuits, a sink and a food-preserving appliance; the handout says a wet bar with a countertop oven is not acceptable. Every ADU and JADU gets its own address before occupancy, with an address fee, and the checklist wants that address in place before the rough framing inspection. Newly constructed units also have to meet the building code's aging-in-place and fall-prevention requirements, and carbon monoxide alarms are required.

    City of Redwood City, ADU handout (August 2026) (opens in a new tab)

  4. Fees, the school district and the closing survey

    Redwood City posts base-fee estimates in three size bands, the smallest also covering a garage conversion, and adds fees case by case on construction valuation. It charges no impact fees on an ADU under 750 square feet. The city must record each ADU with the school district, which decides on its own whether to collect school impact fees. To finalize the building permit, the owner fills in a short ADU Homeowner Survey about rents and use and sends the emailed confirmation to the Building Department.

    City of Redwood City, Accessory Dwelling Unit Ordinance (opens in a new tab)

State license for this work: B General Building. Look up a contractor's license on the CSLB website (cslb.ca.gov).

The work

What gets built behind and inside Redwood City houses

  1. Turning the rear garage into a unit

    A detached garage at the back of a lot can become an ADU on its own footprint and keep its existing setbacks. Redwood City's handout then sets the details a conversion lives with. The garage door cannot serve as the main entrance, so the unit gets a side-hinged swinging door, and the wall that replaces the door must match the house in color and materials. The occupant needs ready access to the electrical panel serving the unit, and the ADU needs its own heating system.

  2. A new cottage from HEART's free plans

    HEART of San Mateo County, with a grant from the Bay Area Air Quality Management District, publishes construction plans for green, all-electric detached ADUs: a 400-square-foot studio, one-bedrooms of 575 and 745 square feet, and an 800-square-foot two-bedroom, each in a contemporary or a traditional style. Redwood City has pre-reviewed them, and users sign a user agreement first. The plans stop at the building; the site plan, foundation, utility sizes, fire flow test and school district fees stay with the owner and the designer.

  3. A junior unit inside an R-1 house

    Redwood City allows a JADU only inside a single-family home on a lot zoned R-1 or RH, one per lot, up to 500 square feet, with up to 150 square feet of expansion to reach an entrance. Interior access to the main house is required when the JADU shares its bathroom, and in that case the owner must live in the JADU or the main home. Neither a JADU nor an ADU may be rented for less than 30 days.

  4. An attached addition that may bring sprinklers

    An attached ADU can reach half the size of the existing home, and its height follows the zoning district instead of the 16-foot cap. The handout warns that fire sprinklers may be required when the house already has them, or when the attached addition plus any substantial remodeling reaches half the main living area or 1,000 square feet, whichever is less. JADUs are exempt. The two units need a one-hour fire separation, and the smoke detectors must be interconnected with the rest of the structure.

Free request

Describe the ADU and garage conversion job once. Local pros who take work in Redwood City reply by call or text.

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Get quotes for ADU and garage conversion work in Redwood City

Two short steps. A local pro who takes this work calls or texts you back.

To send a request, call or text (415) 449-8213.

Free to request, and you agree the scope and price with the person you hire before work starts. In California, a job over $1,000 in labor and materials, or one that needs a building permit, must be done by a contractor licensed by the CSLB in the right class. Ask for the license number and check it at cslb.ca.gov.

A two-story laneway house with a garage, a small detached home at the back of a lot in Vancouver
A two-story laneway house with a garage, a small detached home at the back of a lot in Vancouver. Photo: Mike, CC BY-SA 2.0, via Wikimedia Commons.

The houses here

Rear garages, hillside lots and filled tidelands

Redwood City lots give an ADU very different starting points. In the older neighborhoods many houses keep a garage at the back of the lot, and the city's handout lets a converted structure keep the setbacks it already has, where new construction must stand 4 feet from side and rear lines. In the hills and on the bayfront, the city names foundation design for hillside and bay mud areas as a site-specific item that even a pre-reviewed plan does not settle. Redwood Shores, built on former salt ponds, adds a flood zone statement tied to FEMA's map. Every newly built detached ADU needs a geotechnical soils report, while converting existing living space needs no foundation plan at all.

Part by part

Where a Redwood City lot changes the ADU plan

  • Redwood Shores

    In a FEMA flood hazard area, the ADU's lowest floor must sit above the base flood elevation, and a new structure in a special flood hazard area needs an elevation certificate. The city is redesigning the Shores levees for FEMA reaccreditation, with construction scheduled for 2030 to 2034, so check the parcel's current zone on the city's GIS flood layer before the designer sets a floor height, and expect the soils report to shape the foundation on the fill.

  • Emerald Lake Hills

    These hillside streets carry Redwood City addresses but are unincorporated, so an ADU follows San Mateo County's rules. A single-family lot there can combine one conversion or attached ADU, one detached ADU and one JADU with one more ADU outside the state-exempt types, which may rise to 26 feet. The area has its own county Design Review Officer, and since July 23, 2026 design review outside the Coastal Zone is a staff-level, ministerial step.

  • Downtown, near the Caltrain station

    Within half a mile of a major transit stop, Redwood City lets a detached ADU rise to 18 feet, plus 2 more to match the roof pitch of the house, against 16 feet elsewhere. State law counts an existing rail station as a major transit stop, which puts the downtown Caltrain station at the center of that circle. Confirm with the Planning Division whether your parcel falls inside it before a second-level loft is drawn.

Questions

Questions Redwood City owners ask before an ADU

Does Redwood City require me to live on the property if I add an ADU?

Not for an ADU. The city's August 2026 handout says owner occupancy is not required for ADUs. For a JADU that shares sanitation facilities with the main home, the owner must live in either the JADU or the main house. Short-term rentals of under 30 days are prohibited for both kinds of unit.

Is there a free ADU plan I can use in Redwood City?

Yes. HEART of San Mateo County offers construction plans for four all-electric detached ADUs, from a 400-square-foot studio to an 800-square-foot two-bedroom, at no charge after a user agreement, and Redwood City has pre-reviewed them. The site-specific work is still yours to commission: where the unit sits, its foundation, the utility sizes and the fire flow test.

What is the ADU Homeowner Survey Redwood City asks for?

A short city questionnaire about the new unit, including the rent you expect to charge, which answers state requests for data on ADU rents and how ADUs are used. Redwood City requires it before it will finalize the ADU building permit. Best estimates are accepted, giving an email address is optional, and the emailed confirmation goes to the Building Department.

How many ADUs can go on one Redwood City lot?

On a single-family lot the handout allows one detached ADU, one converted ADU and one JADU. A multifamily lot can add up to eight detached ADUs, never more than the existing units, plus conversions of non-living space up to 25 percent of the existing units. The handout adds that lot coverage, open space and similar limits cannot stop an 800-square-foot ADU.

Can a Redwood City garage conversion keep the old garage door as its entry?

No. The handout says garage doors and patio doors may not be used as the main entrance to an ADU; the unit must be reached through a side-hinged swinging door. Where the garage door comes out, the replacement wall has to match the existing house in color and materials, so plan the siding and paint with the conversion.

Before you hire

What to settle with a Redwood City ADU contractor

  • Who requests the fire flow test from Engineering, and how early, given the city warns the lead time runs to several weeks?
  • Is the geotechnical soils report in your scope, and how does the foundation design deal with bay mud or a slope on this lot?
  • For the garage conversion, how will the replacement wall match the house, and where does the side-hinged entry door go?
  • Will the plan set include the hose-pull diagram, the FEMA flood statement and the utility plan the city's completeness checklist lists?
  • Does the license at cslb.ca.gov show B General Building, and are you building from HEART's free plans or a design in the city's pre-review program?

Where these facts come from

Checked against these public sources in October 2026. Rules and programs change: confirm permit requirements with the city before work starts, and a contractor's license on the CSLB website.

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