Santa Clara County
Sunnyvale ADU rules
Research summary of local ADU rules on file for City of Sunnyvale in Santa Clara County. Not a determination for a specific lot.
City or county ADU page
Check any California address for freeCity of Sunnyvale 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.
How many ADUs
Single-family lots: one new-construction ADU, one conversion ADU and one junior ADU (up to three), but not both a conversion inside the main home and an attached new ADU. No junior ADU on lots with two or more detached homes. Multifamily lots: up to 8 detached ADUs with existing buildings (not more than existing units) or 2 with proposed buildings; conversions of at least one and up to 25% of existing units.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), How many ADUs are permitted, accessed 2026-10-23.
Size
Minimum 150 sq ft. New-construction ADUs on single-family lots up to 1,000 sq ft; conversions have no maximum; junior ADUs up to 500 sq ft.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), ADU Types, accessed 2026-10-23.
Streamlined or not
New ADUs up to 800 sq ft on single-family lots, ADUs on multifamily lots, conversions, junior ADUs and ADUs fully in a new basement need only a building permit. New ADUs over 800 sq ft on single-family lots first need a Miscellaneous Plan Permit (typically 2 to 4 weeks).
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), What permits do I need, accessed 2026-10-23.
Setbacks and height
4 ft side and rear setbacks. Attached: up to 25 ft. Detached: 16 ft (SFH and one-story multifamily); 18 ft with two-story multifamily or within 1/2 mile of major transit; plus 2 ft to match the main roof pitch.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), New Construction ADUs, accessed 2026-10-23.
Extra rules for larger ADUs
ADUs over 800 sq ft also meet front setbacks, put the entrance on a different wall than the main home, keep 5 ft from other buildings, relate in design to the main home, replace removed protected trees, and meet solar-access and window-privacy rules for second floors.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), Additional requirements for Non-Streamlined ADUs, accessed 2026-10-23.
Floor area and lot coverage
Up to 800 sq ft of each ADU is excluded from floor area and lot coverage. Attached covered patios with more than 50% solid roof count; entry porches count toward lot coverage only.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), ADU Basics, accessed 2026-10-23.
Easements
ADUs can’t be built in easements that prohibit permanent structures.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), ADU Basics, accessed 2026-10-23.
Junior ADUs
An internal connection to the main house is allowed, and required if the junior ADU shares a bathroom. An owner-occupancy deed restriction is required only if it shares a bathroom.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), Additional Requirements, accessed 2026-10-23.
Sale and rentals
No separate sale of ADUs or junior ADUs. Short-term rentals are prohibited for ADUs “approved” after Jan. 1, 2020.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), Additional Requirements, accessed 2026-10-23.
Fees
A Transportation Impact Fee applies to ADUs over 750 sq ft; school fees apply to new ADUs of 500 sq ft or more. Sewer and water connection fees are exempt.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), Additional Requirements, accessed 2026-10-23.
Building requirements
Separate entrance for all ADUs. On single-family lots, ADUs (not junior ADUs) need independent heating and water heating, a 100-amp subpanel at the ADU (200 amp at the main home). Attached ADUs: 1-hour fire wall with no doors. Detached ADU sewer may run through the main home’s system; no ejector pumps.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), Fire, Public Works & Building Requirements, accessed 2026-10-23.
Utility billing
For utility rates, a single-family property with an ADU is billed as a two-unit property once the ADU is signed off.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), Additional Requirements, accessed 2026-10-23.
Contact
Planning: planning@sunnyvale.ca.gov, (408) 730-7440. Building: building@sunnyvale.ca.gov, (408) 730-7444.
Source: City of Sunnyvale ADU Brochure (Municipal Code Chapter 19.79), 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 Sunnyvale?
State law sets a baseline for ADUs in Sunnyvale, 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 Sunnyvale Community Development Department, or run a free address summary.
Check any California address for free