Sunnyvale Zoning and ADU Rules: A Home Seller’s Guide

Last updated: November 2026. Reviewed by the Cash Home Buyers CA team.

Sunnyvale allows accessory dwelling units (ADUs) under streamlined rules, and it offers a path to legalize older unpermitted units. Here is what the City says and how it affects a sale.

Sunnyvale ADU rules at a glance

Item	What the City says
Single-family lot	Up to 1 new-construction ADU, 1 conversion ADU and 1 JADU
JADU size	Up to 500 sq ft
Streamlined (building permit only)	New construction of 800 sq ft or less on single-family lots, multifamily new construction, conversions, JADUs and ADUs within a new basement
Over 800 sq ft (single-family lot)	Needs a Miscellaneous Plan Permit first
Contact	Planning 408-730-7440; Permit Center 408-730-7444

Multifamily lots

On multifamily lots the City allows up to 8 existing detached ADUs (not exceeding the existing unit count), up to 2 new detached ADUs, and conversions of at least 1 and no more than 25 percent of existing units.

Legalizing an unpermitted ADU

Sunnyvale allows legalization of an unpermitted ADU or JADU built before January 1, 2020 inside a permitted structure. It also offers five-year deferred enforcement for an ADU built without a permit before that date. The City provides an ADU Calculator and a gallery of pre-approved plans at sunnyvale.aduaccelerator.org/gallery. The City’s page does not list height, setback, parking or fee numbers, so confirm those with Planning.

Selling a home with an ADU

California sellers must disclose known unpermitted construction. A permitted ADU can add value, while an unpermitted one may be flagged by the buyer’s inspector and lender. Options: legalize it first, credit the buyer, or sell as-is for cash.

Seller checklist

• Confirm the ADU or JADU has a final permit in E-OneStop.
• If built before January 1, 2020 without a permit, ask Planning about legalization or deferred enforcement.
• Check that you do not have both a conversion ADU in the main building and an attached new-construction ADU, which the City does not allow on a single-family lot.
• Keep plans, invoices and inspection sign-offs.

Closing costs

Santa Clara County’s documentary transfer tax is $0.55 per $500 of sale price, or $660 on a $600,000 sale.

How to sell a house in Sunnyvale

1. Review your ADU and permit records.
2. Decide whether to legalize, credit, or sell as-is.
3. Request a cash offer from us.
4. Pick a closing date, often within days.
5. Close through escrow and get paid.

Sunnyvale ADU size, height and setback standards

The City’s ADU brochure lays out the numbers owners run into most. Every new-construction, conversion and junior ADU must be at least 150 square feet. A new-construction ADU on a single-family lot can be up to 1,000 square feet, a junior ADU is capped at 500 square feet, and a conversion ADU has no stated maximum because it lives inside space that already exists.

Standard	What the City brochure says
Attached new-construction ADU height	Up to 25 feet
Detached ADU on a single-family or one-story multifamily lot	Up to 16 feet
Two or more story multifamily, or lots within one-half mile walking distance of a major transit stop or high-quality transit corridor	Up to 18 feet
Roof pitch allowance	An additional 2 feet to align with the main home’s roof pitch
Side and rear setbacks for new construction	Minimum 4 feet
Non-streamlined ADUs	Front and reducible front-yard setbacks follow the zoning district

Because these are minimums and maximums, a backyard unit that was built a little taller or closer to a fence than the table allows is a common reason a sale gets complicated. If you are not sure which category your unit falls into, ask the Planning Division before you list.

Fees that can follow an ADU

The brochure points to two impact fees owners should know about. A Transportation Impact Fee applies to ADUs over 750 square feet, and a school impact fee applies to new-construction ADUs with 500 square feet or more of living area, paid to the applicable school district. Incremental sewer and water connection fees are exempt. The City gives a typical review timeline of two to four weeks from fee payment.

None of this means a buyer will pay these fees on a finished unit, but an unfinished or never-closed ADU permit can leave an open fee question. Check the permit status in E-OneStop before you assume a unit is complete.

JADU rules in plain terms

• A junior ADU must be entirely contained within the walls of the main building of an existing or proposed single-family home.
• Only one JADU is allowed on a single-family lot, and none are allowed on multifamily lots.
• JADUs are not permitted on lots with two or more detached single-family units.
• An owner-occupancy deed restriction is required if the JADU shares sanitation facilities with the main home.

A single-family lot can therefore carry up to three additional units in total: one new-construction ADU, one conversion ADU and one JADU.

Who to contact in Sunnyvale

The One-Stop Permit Center is at 456 W. Olive Ave, Sunnyvale, CA 94086. The brochure lists the Planning Division at planning@sunnyvale.ca.gov or (408) 730-7440 and the Building Division at building@sunnyvale.ca.gov or (408) 730-7444. Planning answers zoning and setback questions, and Building handles the permit and inspection side. For a sale, ask both for a written status on any ADU or addition.

Zoning questions to settle before listing

• Does the ADU type on your lot match one of the types the City recognizes (new construction, conversion or JADU)?
• Is the unit within the size, height and setback limits above?
• Was it built under a permit that was finaled, or is there an open permit?
• If a JADU shares a bathroom with the main home, is the owner-occupancy deed restriction recorded?
• Would a lender or appraiser count the unit as legal living space?

If several of these answers are uncertain, selling as-is to a cash buyer can avoid months of legalization work. You still disclose what you know, and the price reflects the condition.

Streamlined versus Miscellaneous Plan Permit

New construction of 800 square feet or less on single-family lots, conversions, JADUs and ADUs within a new basement are streamlined, with a building permit only. A single-family lot ADU over 800 square feet needs a Miscellaneous Plan Permit first. If an existing unit is larger than 800 square feet, ask Planning at 408-730-7440 which path applies.

Deferred enforcement for older units

The city offers five-year deferred enforcement for an ADU built without a permit before January 1, 2020, and allows legalization of an unpermitted ADU or JADU built before that date inside a permitted structure. A buyer will want to know whether the unit relies on that deferral, because it has a time limit.

The ADU Calculator and gallery

The city provides an ADU Calculator and a gallery of pre-approved plans at sunnyvale.aduaccelerator.org/gallery. Use the calculator to estimate what a legalization might involve and the gallery to compare an existing unit with approved designs. Confirm height, setback and parking figures with Planning, because the city’s page does not list them.

Frequently asked questions

How many ADUs can a Sunnyvale single-family lot have?

Up to one new-construction ADU, one conversion ADU and one JADU.

How large can a JADU be?

Up to 500 sq ft.

Can I legalize an unpermitted ADU?

Yes, if built before January 1, 2020 inside a permitted structure, with five-year deferred enforcement also available.

Can I sell with an unpermitted ADU?

Yes, with disclosure. A cash buyer can purchase as-is.

What is the maximum size of a new ADU in Sunnyvale?

The City’s ADU brochure lists 1,000 square feet for a new-construction ADU on a single-family lot, 500 square feet for a JADU, and a 150 square foot minimum for each type.

How tall can a detached ADU be in Sunnyvale?

The brochure lists 16 feet for a detached ADU on a single-family or one-story multifamily lot, and 18 feet for two-story multifamily lots and lots within one-half mile walking distance of a major transit stop. An extra 2 feet is allowed to match the main home’s roof pitch.

Do Sunnyvale ADUs have impact fees?

The brochure says a Transportation Impact Fee applies to ADUs over 750 square feet and a school impact fee applies to new-construction ADUs of 500 square feet or more. Incremental sewer and water connection fees are exempt.

Who do I call about ADU zoning in Sunnyvale?

Planning is at (408) 730-7440 and Building is at (408) 730-7444, both at the One-Stop Permit Center, 456 W. Olive Ave.

How many ADUs can a Sunnyvale single-family lot have?

Up to one new-construction ADU, one conversion ADU and one JADU, according to the city.

Can I legalize an older Sunnyvale ADU?

The city allows legalization of an unpermitted ADU or JADU built before January 1, 2020 inside a permitted structure and offers five-year deferred enforcement.

More guides

• Sunnyvale permits guide
• Sunnyvale code enforcement guide
• Santa Clara County property tax guide

Sources

• City of Sunnyvale, Permits and ADU information

This guide is general information, not legal advice. Confirm current rules with the City of Sunnyvale.