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Building an ADU in Sunnyvale

The lever is the 800 sq ft line: a detached unit under 800 sq ft on a single-family lot is building-permit-only, while 800 sq ft and up needs a Miscellaneous Plan Permit and replacement of any uncovered parking removed. Size caps sit below the state default.

Check a Sunnyvale address → Sunnyvale's ADU page →

Pre-approved plans

Checked 2026-09-10

Pre-approved plans gallery on the county's ADU Accelerator platform; plans are bought from the designer and get a streamlined review. Under state law a detached unit built from a pre-approved plan gets a 30-day decision instead of 60.

Program page →

Programs and incentives

Active
Building-permit-only path under 800 sq ft

Interior conversions and new detached units under 800 sq ft on single-family lots need a building permit only, with no planning approval.

Sunnyvale's page → Checked 2026-09-10
Active
Five-year deferred enforcement for pre-2020 units

Owners of an unpermitted ADU built before 2020 can request five-year deferred enforcement while life-safety items are verified.

Sunnyvale's page → Checked 2026-09-10

Local rules worth knowing

Maximum size. New detached or attached units: 850 sq ft (studio or one bedroom) or 1,000 sq ft (two or more bedrooms). Interior conversions have no maximum. Source →
Height. Detached 16 ft, or 18 ft near transit. Attached up to 25 ft or the main home's height, whichever is lower.
Parking. None required, except a detached unit of 800 sq ft or more must replace uncovered spaces it removes.
JADU. Up to 500 sq ft inside the walls of the house; owner occupancy required.
Short-term rental. Only ADUs built before 2020 may be used as short-term rentals; everything since is 30-day minimum.

Who issues the permit

If the parcel is inside Sunnyvale city limits, the City issues the permit and its ordinance applies on top of state law. Just outside the line it is Santa Clara County instead, with different standards.

Sunnyvale's ADU page → Planning department → Online permit portal →

Contact. One-Stop Permit Center (408) 730-7444, building@sunnyvale.ca.gov, planning@sunnyvale.ca.gov.

Review time

Streamlined units skip planning review entirely. No published plan-check turnaround; the state 60-day decision applies.

Fees

Exempt from city impact fees under 750 sq ft; school fees still apply; utility connection fees apply except for interior conversions.

How this was checked

Last gone over September 10, 2026. Verification: the city's own pages or ordinance text were opened and read. Programmes get suspended, capped and restarted; the links are the authority. Ask Keyli and she searches Sunnyvale's own site live rather than answering from memory.

What's true in Sunnyvale because it's true everywhere

State law sets a floor no ordinance can go under. The full guide, with every statute cited →

An ADU is allowed on your lot

Every lot zoned for residential use may have at least one ADU, and a single-family lot may also add a JADU. A city cannot say no to the category.

800 sq ft by right

A detached or attached unit of up to 800 sq ft, 16 ft tall, with 4 ft side and rear setbacks must be approved regardless of local lot-coverage or floor-area limits.

Four-foot setbacks

A city cannot require more than four feet from side and rear lot lines for an ADU.

A 60-day decision

Once your application is complete the city has 60 days to approve or deny; 30 if you build from a pre-approved plan.

No replacement parking

Convert or demolish a garage to build an ADU and the spaces you lose never have to be replaced.

No impact fees under 750 sq ft

Prohibited entirely below 750 square feet, and proportional above it.

Ministerial review

Reviewed against an objective checklist. No design review board, no hearing, no discretion about whether they like it.

No owner-occupancy rule for an ADU

A city cannot require you to live on the property for a standard ADU. A JADU is different: since 1 January 2026 owner occupancy is required when the JADU shares sanitation with the main house.

We build here

Sunnyvale is inside our service area, and ADUs are all we do. We bring in the architect and engineer or work with yours, run the permit with Sunnyvale, and build with our own crew: about 6 weeks of construction for a detached unit once the permit is in hand.

What we can't tell you from here is what your particular lot will take: setbacks, the sewer lateral, the panel, grade and access. That is what the free site walk is for.