Sunnyvale / ADU construction
ADU Construction in Sunnyvale
Keep a Sunnyvale ADU at 800 square feet and it needs only a building permit.
Sunnyvale streamlines new ADUs up to 800 square feet; larger ones need a planning permit first. We design and build ADUs here with the size, height and utility rules settled before a floor plan is drawn.
SUNNYVALE AT A GLANCE
How Sunnyvale handles ADUs.
Sunnyvale streamlines most ADUs, bills a lot with an ADU as two units, and still relies on PG&E for the wires and the meter. Here is who does what.
- 800
- square feet: the largest new ADU that needs only a building permit
- 2 to 4
- weeks typical planning review for a larger ADU, after fee payment
- 56%
- of Sunnyvale households rent
Permits
One-Stop Permit Center
Building permits, planning permits and inspections run through E-OneStop. The center is at City Hall, 456 W. Olive Ave.; Planning answers ADU questions at (408) 730-7440.
(408) 730-7444ADU permits ↗ADU brochure ↗Plans
Pre-approved plan gallery
Sunnyvale's online ADU plan gallery lists pre-approved plans with a streamlined permit path, and the city links a free Santa Clara County ADU guidebook.
ADU plan gallery ↗Utilities
PG&E service, city billing
The city's brochure calls for a 100 amp subpanel at the ADU and 200 amps at the main house, and says to check PG&E for upgrade availability. City utility rates switch to two units at sign-off.
(877) 743-7782STREAMLINED OR NOT
800 square feet is the line.
On a single-family lot, a new ADU up to 800 square feet goes straight to a building permit. Above that, up to the 1,000 square foot maximum, a Miscellaneous Plan Permit comes first, with a typical review of 2 to 4 weeks after the fee is paid. Height is 16 feet for a detached ADU, or 18 feet near major transit.
Detached ADU
Up to 1,000 square feet, 4 foot side and rear setbacks, 16 feet high, or 18 feet within a half mile walk of major transit.
Attached ADU
A physical expansion of the main house, up to 25 feet high. It cannot be combined with a conversion ADU inside the main house.
Conversion ADU
Built from part of the house or an accessory structure, with no maximum size and streamlined review.
Junior ADU
Up to 500 square feet inside the main home. An owner-occupancy deed restriction applies if it shares a bathroom.
Electrical and sewer
A 100 amp subpanel at the ADU and 200 amps at the main house; the sewer ties in downstream of the main kitchen sink, with no ejector pump.
Multifamily lots
Up to 8 detached ADUs on an existing multifamily lot, not exceeding the number of existing units, plus conversions of up to 25 percent of the existing units.
SMC CHAPTER 19.79
Streamlined or non-streamlined.
Sunnyvale's ADU brochure splits review into two tracks. Most owners aim for the streamlined path by holding a new unit to 800 square feet.
| Streamlined | Non-streamlined | |
|---|---|---|
| Applies to | New ADUs to 800 sq ft, conversions, JADUs, basements | New ADUs over 800 sq ft on single-family lots |
| Permits | Building permit only | Miscellaneous Plan Permit, then building permit |
| Side and rear setbacks | 4 ft | 4 ft |
| Front setback | Not listed | Per zoning district |
| Distance from main house | Not listed | 5 ft wall to wall |
| Extra design rules | None listed | Separate entrance plane, design match, solar access and privacy for two stories |
Source: City of Sunnyvale ADU brochure ↗
Planning the work
How a Sunnyvale ADU gets built.
Lot check
Free visit. Setbacks, transit distance for height, sewer route, panel size and PG&E service.
Design
Custom plans or a plan from the city's pre-approved gallery, sized to the streamlined limit where possible.
Permits
Building permit through E-OneStop, with a Miscellaneous Plan Permit first for an ADU over 800 square feet.
Build and final
Foundation, framing, rough-in inspections booked online or at (408) 730-7790, final and utility billing set up.
FIRE, PUBLIC WORKS AND BUILDING
What a Sunnyvale ADU has to include.
Required for a single-family ADU
- Separate entrance
- Independent space and water heating
- 100 amp subpanel at the ADU, 200 amps at the main house
- Sewer tied in downstream of the main kitchen, no ejector pump
Fire sprinklers needed when
- The main house has sprinklers
- A detached ADU is beyond 150 feet of hose reach
- An attached ADU joins a sprinklered house
Fees and limits
- Transportation Impact Fee over 750 sq ft
- School impact fee at 500 sq ft or more of living area
- 4 inch sewer upgrade if the site exceeds 5 toilets
- No ADU inside an easement that bars structures
WHAT SURPRISES SUNNYVALE ADU OWNERS
Problems Sunnyvale owners run into, and how we plan around them.
From r/Sunnyvale threads and the city's ADU brochure.
The sewer and trash bill jumps to two units once the ADU is finished.
We tell owners at design that city utility rates switch to two units at sign-off, so it is in the rental math from day one.
Getting a separate address for mail, deliveries and utilities is unclear.
The address request goes to the city during permitting, and the number is posted where deliveries can see it.
Plans take a couple of rounds before approval.
Height, setbacks, sewer route and panel size are checked against the brochure before submittal to cut resubmittals.
Legalizing an existing unit sounds expensive and uncertain.
We pre-inspect the unit and check whether it was built before January 1, 2020, which opens reduced standards and deferred enforcement.
A PG&E service upgrade can take months.
The subpanel and service size are settled during design, and any PG&E application is filed with the city permit.
Sources: r/Sunnyvale threads, 2024 to 2026; City of Sunnyvale ADU brochure and ADU permit page.
How big can an ADU be in Sunnyvale?
Up to 1,000 square feet for a new-construction ADU on a single-family lot, and 800 square feet or less qualifies for streamlined review. Conversion ADUs have no maximum size, junior ADUs are capped at 500 square feet, and every ADU must be at least 150 square feet.
How tall can a detached ADU be in Sunnyvale?
16 feet on a single-family lot, or 18 feet within a half-mile walk of a major transit stop or high-quality transit corridor. Another 2 feet is allowed for a roof pitch that matches the main house. Attached ADUs can reach 25 feet, measured from average finished grade within 5 feet of the structure.
Do I need a planning permit for an ADU in Sunnyvale?
No, not for a new ADU of 800 square feet or less, a conversion or a junior ADU; those need only a building permit. A new ADU over 800 square feet first needs a Miscellaneous Plan Permit, with a typical review of 2 to 4 weeks after the fee is paid.
What impact fees apply to an ADU in Sunnyvale?
Two can apply: a Transportation Impact Fee for ADUs over 750 square feet, and a school impact fee for new-construction ADUs with 500 square feet or more of living area, paid to the school district. Incremental sewer and water connection fees are exempt.
Does an ADU change my utility bill in Sunnyvale?
Yes. For city utility rates, a single-family property with an ADU is billed as a multi-family property with two units, starting the day the ADU is signed off. Separate sale of the ADU is prohibited, and short-term rentals are banned for ADUs approved after January 1, 2020.
Can I legalize an existing unpermitted ADU in Sunnyvale?
Yes, if it was built inside a permitted structure before January 1, 2020; the city may apply reduced standards if the unit is safe to live in. Owners of such units can also request a five-year deferred enforcement. Units built after that date must meet the rules for new ADUs.
