San Mateo County
Redwood City ADU rules
Research summary of local ADU rules on file for City of Redwood City in San Mateo County. Not a determination for a specific lot.
City or county ADU page
Check any California address for freeCity of Redwood City rules on file
Local rules recorded in this project for this jurisdiction. Where a city figure on file is stricter than the state baseline on file, both are shown.
Owner occupancy
Not required for ADUs. For junior ADUs, the owner must live in the junior ADU or the main home only when the junior ADU shares a bathroom.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Occupancy & Short-term Rentals, accessed 2026-10-23.
Short-term rentals
Rentals under 30 days are prohibited for ADUs and junior ADUs.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Occupancy & Short-term Rentals, accessed 2026-10-23.
Where allowed
ADUs: all residential and mixed-use zones, with limited exceptions (traffic flow, water, sewer or public safety). Junior ADUs: only in single-family homes on R-1 and RH lots.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Zones Allowed, accessed 2026-10-23.
How many
Single-family lots: one detached ADU, one converted ADU and one junior ADU. Multifamily lots: up to eight detached ADUs (not more than the existing units; two for proposed multifamily buildings) plus conversions of non-living space up to 25% of existing units.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Number of Units, accessed 2026-10-23.
Detached ADU size
Minimum 150 sq ft. Maximum 850 sq ft for studios and one-bedrooms, 1,200 sq ft for two or more bedrooms.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), ADU Size, accessed 2026-10-23.
Junior ADUs
Up to 500 sq ft, plus up to 150 sq ft for an entrance. Interior access is required if it shares a bathroom with the main home.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), JADU Size & Design Guidelines, accessed 2026-10-23.
Height
Detached: 16 ft; 18 ft within 1/2 mile of a major transit stop plus 2 ft for roof pitch; 18 ft on multifamily lots. Attached: up to the zone’s limit.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Maximum ADU Height, accessed 2026-10-23.
Setbacks
New construction: 4 ft side and rear. Converted structures keep their existing setbacks.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Setbacks, accessed 2026-10-23.
Lot coverage and open space
Lot coverage, pervious area, open space and accessory-structure rules apply, but they cannot prevent an 800 sq ft ADU.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Lot or Location Restrictions, accessed 2026-10-23.
Parking
No new off-street parking is required for ADUs or junior ADUs.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), Parking, accessed 2026-10-23.
Fire and water supply
Fire sprinklers may be required if the house already has them, or if the attached ADU addition plus remodeling reaches 50% of the main living area or 1,000 sq ft, whichever is less (junior ADUs exempt). A fire flow test showing enough water supply is required, with a fee to Engineering.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), General Fire and Building Safety Requirements, accessed 2026-10-23.
Building details
One-hour fire separation from the main house; interconnected smoke alarms and CO alarms; ready access to the electrical panel; a separate heating system; a kitchen with stove/oven, sink and refrigerator (a wet bar with countertop oven does not count); a side-hinged entry door (not a garage or patio door); a new address before occupancy.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), General Fire and Building Safety Requirements, accessed 2026-10-23.
Pre-reviewed plans
The City runs a pre-reviewed plan program that cuts review to 30 days, and offers free pre-reviewed all-electric detached plans through HEART’s GLADUR program. Site-specific review still applies.
Source: City of Redwood City Accessory Dwelling Unit Ordinance page, Pre-Reviewed ADU Plans, accessed 2026-10-23.
How to apply
Fill out the ADU Completeness Checklist and apply for a building permit through eTrakIt (permits.redwoodcity.org). Planning: planning@redwoodcity.org, 650-780-7234.
Source: City of Redwood City Accessory Dwelling Units handout (Effective August 2026), accessed 2026-10-23.
California state rules on file
The statewide baseline recorded from state law and the HCD ADU Handbook.
Detached size cap described in state law
1,200 sq ft. Recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Side and rear setback cap for a new ADU
4 ft. Recorded in this rules file from Government Code section 66314, which describes a cap on side and rear setbacks for a new ADU.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Setback for a conversion of an existing structure
No additional setback, as recorded in this rules file from Government Code section 66314 for a conversion of an existing structure.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Minimum lot size
A city may not impose a minimum lot size for an ADU, as recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Minimum unit the handbook says cities must allow
At least an 800 sq ft ADU with 4 ft side and rear setbacks. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(3).
Source: HCD ADU Handbook, 66321(b)(3); handbook updated March 2026, accessed 2026-10-16.
Detached height described in the handbook
16 ft, or 18 ft or 20 ft in some cases. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(4).
Source: HCD ADU Handbook, 66321(b)(4); handbook updated March 2026, accessed 2026-10-16.
Permit decision deadline
60 days. Recorded in this rules file from Government Code section 66317(a)(3): the permitting agency must decide on (approve or deny) a completed ADU application within 60 days when an existing single-family or multifamily dwelling is on the lot. Section 66317(a)(1) says the application is considered ministerially, without discretionary review or a hearing.
Source: California Government Code section 66317, 66317(a)(1), (a)(3), accessed 2026-10-17.
Owner-occupancy requirement
None. Recorded in this rules file from Government Code section 66315: a local agency may not impose an owner-occupancy requirement on an ADU. It may require that the property be used for rentals of terms 30 days or longer. The HCD ADU Handbook (updated March 2026) describes the same rule.
Source: California Government Code section 66315, 66315; HCD ADU Handbook updated March 2026, accessed 2026-10-17.
Parking near public transit
No parking standards within one-half mile walking distance of public transit. Recorded in this rules file from Government Code section 66322(a)(1). Section 66322(a) lists several other cases where parking standards may not be imposed.
Source: California Government Code section 66322, 66322(a), accessed 2026-10-17.
Ministerial categories
The HCD ADU Handbook (updated March 2026) states that Government Code section 66323 sets four ministerial categories. This rules file does not restate those four categories.
Source: HCD ADU Handbook, 66323; handbook updated March 2026, accessed 2026-10-16.
Fire Hazard Severity Zones
If your lot is in a Fire Hazard Severity Zone, the CAL FIRE Office of the State Fire Marshal says in Information Bulletin 25-004 (issued March 3, 2025): “Fire Hazard Severity Zones (FHSZs) should not restrict the development of Accessory Dwelling Units (ADUs). However, additional building standards may be necessary, including but not limited to California Fire Code Chapter 49 and California Building Code Chapter 7A.” State ADU law does not itself bar an ADU there. A city or county may still apply its building code, including wildfire-resistant construction (Gov. Code 66314(d)(8)); require side and rear setbacks “sufficient for fire and safety” for a unit converted under 66323(a)(1); and decline parking in setbacks on specific fire and life safety findings (66314(d)(10)(B)). It may also consider public safety when it designates where ADUs may be permitted (66314(a)). Sprinklers can't be required in an ADU or JADU if the primary residence doesn't need them (66314(d)(12), 66323(d)). Some cities and counties still apply their own fire-zone limits. Where this summary has one, it is listed with the local rules. This summary does not look up your lot. Check the CAL FIRE Fire Hazard Severity Zone map viewer linked from the State Fire Marshal's Fire Hazard Severity Zones page: https://experience.arcgis.com/experience/5065c998b4b0462f9ec3c6c226c610a9
Source: CAL FIRE Office of the State Fire Marshal Information Bulletin 25-004, page 4, issued March 3, 2025; Gov. Code 66314, 66323, accessed 2026-10-20.
State baseline on the directory → · State ADU rules on the homepage →
Can I build an ADU in Redwood City?
State law sets a baseline for ADUs in Redwood City, and the local standards on file are listed on this page. Whether a specific lot can add an ADU depends on zoning, utilities, and other site facts this page does not measure. Confirm with City of Redwood City Planning Division, or run a free address summary.
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