Building an ADU in Sunnyvale

What you can build in Sunnyvale

ADUs are allowed on residential and residential mixed-use lots with an existing or proposed single-family home or multifamily building. Sunnyvale counts a duplex as multifamily. Several detached homes on one lot count as single-family. Townhomes on their own lots may count as single-family too.

• Single-family lot: one conversion ADU, one new construction ADU and one junior ADU, "in any order." You can't have both a conversion ADU inside the house and an attached new ADU. Lots with several detached homes can have one conversion ADU and one new construction ADU, but no JADU.
• Multifamily lot, existing building: up to eight detached ADUs (no more than the number of existing units), plus conversions of non-living space such as storage rooms, attics, basements or garages for at least one ADU and up to 25% of the units.
• Multifamily lot, proposed building: up to two detached ADUs.

ADUs are also allowed on properties in the city's Heritage Resource Inventory, with no extra permit or public review. Your approval can't be conditioned on fixing nonconforming zoning conditions or unpermitted structures that aren't a health and safety threat and aren't affected by the ADU. [1][2][4]

Streamlined vs. non-streamlined review

Sunnyvale sorts ADUs into two review tracks:

• Streamlined (building permit only): new ADUs up to 800 sq ft on single-family lots, detached ADUs on multifamily lots, conversion ADUs, JADUs, and ADUs fully inside a basement. These must still meet the 4-foot side and rear setbacks and height limits.
• Non-streamlined (Miscellaneous Plan Permit first): new ADUs over 800 sq ft on single-family lots. The community development director "shall ministerially approve" the permit. The city's brochure says MPP review typically takes 2 to 4 weeks from fee payment.

Non-streamlined ADUs must also meet extra rules: the zone's front setbacks, 5 feet from the main home and other accessory buildings (detached), an entrance not on the same street-facing wall as the house, matching materials for attached ADUs, and, for second-floor units, solar access rules, plus window privacy for second-story windows near side and rear lot lines (sills at least 5 feet up or obscured glass). Area over 800 sq ft counts toward lot coverage and floor area ratio. [1][2][3]

Size, height and setbacks

A new construction ADU on a single-family lot can be up to 1,000 sq ft, with no limit on bedrooms. Every ADU must be at least 150 sq ft. Sunnyvale measures ADU area "from the outside dimensions of a building or wall." Up to 800 sq ft of each ADU is exempt from lot coverage and floor area limits. Conversion ADUs have no maximum size, and a converted accessory building can grow by up to 150 sq ft for a way in and out. A JADU can be up to 500 sq ft.

Height is measured from the average finished grade within 5 feet of the building:

• Detached ADU: 16 feet on single-family and one-story multifamily lots.
• Detached ADU: 18 feet within a half mile walk of a major transit stop or high-quality transit corridor, plus 2 feet to match the main home's roof pitch.
• Detached ADU on a lot with a multistory multifamily building: 18 feet.
• Attached ADU: 25 feet or the main building's height limit, whichever is lower.
• No ADU can be more than two stories. Balconies, second-story decks and rooftop terraces are not allowed on second-floor or two-story ADUs.

Setbacks. New construction needs 4 feet from side and rear lot lines. Less is allowed if you rebuild in the same spot and size as an existing structure you demolish. ADUs can't go in easements that bar permanent structures. [1][3]

Parking

Sunnyvale requires no off-street parking for an ADU. You don't have to replace covered parking you remove or demolish to build an ADU or to convert space into one. [1]

Fees and utilities

Your building permit fee depends on your ADU's size. Non-streamlined ADUs also pay the Planning Division's MPP fee. The city's ADU Calculator gives a rough estimate of costs, fees and rents.

• Transportation impact fee: only for ADUs over 750 sq ft.
• School impact fee: for new construction ADUs with 500 sq ft or more of living area, paid to your school district.
• Utility connection fees: incremental sewer and water connection fees are waived for single-family ADUs. JADUs and conversion ADUs (unless built with a new home) don't need a new utility connection.

Sunnyvale's code says no impact fees apply to an ADU "less than 750 square feet." State law sets the line at 750 sq ft or less of interior living space, with fees proportional to the main home above that. For utility billing, a single-family home with an ADU is billed at two-unit multifamily rates once the ADU is finished. See our ADU cost guide and financing guide. [1][3][4][5]

How long it takes

Sunnyvale's code repeats state law: the city must tell you within 15 business days whether your application is complete, and approve or deny a complete application within 60 days when there's already a home on the lot. The city's toolkit estimates 1 to 6 months for permitting and 2 to 12 months for construction. Pre-approved plans from the city's gallery are processed within 30 days. See our ADU permit process guide. [1][4]

Fire and building requirements

The city's brochure lists these building rules for ADUs on single-family lots:

• Fire sprinklers: needed in an attached ADU if the main home has them. Needed in a detached ADU if the main home has them, or if fire hose reach of 150 feet doesn't cover every part of the building.
• Separation: an attached ADU needs a 1-hour fire-rated wall with no door openings to the house.
• Systems: ADUs need their own space and water heating. The brochure calls for a 100-amp subpanel at the ADU and 200 amps at the main home; check with PG&E about upgrades.
• Sewer: a detached ADU's line can connect downstream of the house's kitchen sink; ejector pumps aren't allowed. If the site has more than five toilets, the building sewer must be upgraded to a 4-inch line.

For multifamily ADUs, contact the Building Division at (408) 730-7444. [3]

Garage conversions, junior ADUs and legalization

You can convert part of your home, an attached garage, or an existing accessory building into a conversion ADU with no maximum size. Conversions get streamlined review. See our garage conversion guide.

A junior ADU must be inside the walls of a single-family home, which can include an attached garage. It can't be built as a new addition or in a detached building. It needs an efficiency kitchen. If it shares a bathroom with the house, it needs an inside connecting door, and the owner must live in the JADU or the house. Before the permit is issued, you record a covenant that the JADU won't be sold separately, stays within 500 sq ft, and is rented only for terms longer than 30 days. The code requires owner occupancy when the JADU shares a bathroom, which matches state law since 2026. But the required covenant also says one unit on the lot "shall remain owner-occupied," so if your JADU has its own bathroom, ask the Planning Division how this applies.

If you built an ADU or JADU inside a permitted structure before January 1, 2020, you can apply to legalize it. The city "may use reduced development standards" if the unit is safe to live in. You can also ask for a five-year deferral of enforcement through the Community Development Department. [1][2][3][5]

Renting, selling and lot splits

You can rent an ADU separately from the main home. ADUs approved on or after January 1, 2020, can't be used as short-term rentals. An ADU can't be sold separately except under Gov. Code 66341, and the city "has not elected to allow" ADU condominiums under Gov. Code 66342.

If you split your lot under SB 9 (Sunnyvale's urban lot split rules), each new lot can have one single-family home plus one ADU or JADU, for two units at most. If a lot already has two "dual urban opportunity units," no ADUs are allowed. See our SB 9 lot split guide.

In December 2022, HCD, the state housing agency, found Sunnyvale's 2021 ADU ordinance out of compliance on points including a rule barring the ADU entrance from facing the street on the same wall as the house. The city adopted a new ADU chapter in April 2025 (Ordinance 3240-25) and amended it in July 2026 (Ordinance 3258-26); the entrance rule now applies only to non-streamlined ADUs. See our California ADU law overview. [1][6]

Permit steps in Sunnyvale

1. Check your lot type and ADU options

   Read the Sunnyvale ADU Brochure and the ADU Toolkit to see whether your lot counts as single-family or multifamily and which ADUs you can add. [2][3]

2. Talk to the Permit Center

   Call the Planning Division at (408) 730-7440 or the Permit Center at (408) 730-7444, or visit the One-Stop Permit Center at City Hall, 456 W. Olive Ave. Staff explain the process and documents you need. [3][7]

3. Design the ADU or pick a pre-approved plan

   Work with an architect or contractor, or choose a design from the ADU Plans Gallery and contact its designer. [2][4]

4. Apply for an MPP first if over 800 sq ft

   For a new ADU over 800 sq ft on a single-family lot, apply online for a Miscellaneous Plan Permit. A planner contacts you and sends an invoice; review typically takes 2 to 4 weeks after you pay. [2][3]

5. Apply for the building permit online

   Submit plans and pay fees through the city's E-OneStop online permitting system, which you also use to answer comments and schedule inspections. See the Permit Center page for help. [4][7]

6. Respond to plan review and get your permit

   Answer plan review comments and resubmit as needed. The city issues the permit once all reviewers approve and fees are paid. For a JADU, record the deed restriction covenant before issuance. [1][4]

7. Build and pass inspections

   Post your approved construction documents on site and schedule inspections as you build. The city finals the permit when the work matches the plans. [4]

Pre-approved and sample plans

• ADU Plans Gallery

  Pre-approved detached new construction ADU plans already reviewed for building code; pick a plan, contact the designer and apply, with processing within 30 days. [2][4]

Who to call

• Planning Division

  ADU zoning standards and MPP applications (planning@sunnyvale.ca.gov)

  (408) 730-7440

  City Hall, 456 W. Olive Ave., Sunnyvale, CA 94086

  [3][7]

• Building Division / One-Stop Permit Center

  Building permits, plan check, inspections and legalization (building@sunnyvale.ca.gov)

  (408) 730-7444

  456 W. Olive Ave., 2nd floor, Sunnyvale, CA 94086

  [3][7]

• Fire Protection Engineering

  Fire sprinkler and hose-reach questions

  408-730-7212

  [7]

Questions people ask