Santa Rosa Zoning and ADU Guide for Homeowners

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Last updated November 13, 2026. Reviewed by the Cash Home Buyers CA team.

Santa Rosa’s accessory dwelling unit standards live in Section 20-42.130 of the city’s Zoning Code. They set four-foot side and rear setbacks for new units, a height limit that depends on stories and transit access, size caps for detached, attached and converted units, parking rules with several exemptions, and extra setbacks in hillside and creekside areas.

This guide summarizes those standards in plain language and explains what they mean when a house has an unpermitted or non-conforming unit and the owner wants to sell.

Santa Rosa ADU standards at a glance

Code section	Santa Rosa Zoning Code, Section 20-42.130 (Accessory Dwelling Units)
Units per single-family lot	Up to two ADUs and one junior ADU
New detached unit size	Up to 1,200 square feet of habitable space
Junior ADU size	Up to 500 square feet
Side and rear setbacks	4 feet for new attached or detached units
One-story height	16 feet, 18 feet near major transit; 25 feet if attached; 27 feet absolute cap
Parking	One space, with exemptions
Fire plan review	Santa Rosa Fire Department Plan Review, 707-543-3524

How many units a lot can have

On a lot with a proposed or existing single-family home, the code allows up to two accessory dwelling units plus one junior ADU.

The two ADUs break down into one new attached or detached unit and one unit created inside the converted space of the house or an existing accessory structure, and the junior ADU is separate.

On multifamily property, the number of ADUs inside the building is capped at 25 percent of existing units, with at least one always allowed.

Only one junior ADU is permitted per parcel, and the code ties some placements to the width of the street serving the parcel, such as a 36-foot street with parking on both sides or a 30-foot street with parking on one side.

Setbacks

A new attached or detached ADU needs a minimum four-foot side setback and four-foot rear setback, with a front setback matching the main home’s zoning district. Side-corner setbacks are a minimum of eight feet.

An ADU built above a legally constructed or proposed garage needs five feet from the side and rear lines.

A detached unit of up to 800 square feet that meets height limits may not be blocked by local standards, and an 800-square-foot unit may even be placed in the front setback if no other part of the lot can accommodate it.

Where an ADU abuts an R-3 district, no side or rear minimum applies. New units must also leave room for the future width of abutting public streets, so ask the city whether a right-of-way reservation applies.

Size limits

A new detached ADU cannot exceed 1,200 square feet of habitable space.

A unit created entirely by converting part of an existing or proposed single-family home cannot occupy more than 45 percent of the existing habitable space, excluding the garage, nor exceed 1,200 square feet, but the code guarantees 850 square feet for a studio or one-bedroom unit and 1,000 square feet for a unit with more than one bedroom.

A conversion of a detached accessory structure can reach 1,200 square feet. A junior ADU can never exceed 500 square feet of habitable space.

Height

A one-story ADU is limited to 16 feet. A detached ADU within half a mile walking distance of a major transit stop or high-quality transit corridor can reach 18 feet, and 18 feet also applies to a detached ADU on a multifamily, multistory lot.

An ADU attached to the primary home may reach 25 feet. A two-story ADU is limited to 27 feet, and the whole structure may not exceed 27 feet when an ADU sits above a garage or carport. No ADU may exceed 27 feet.

Parking

The code asks for one off-street space per ADU, but exempts units that are 750 square feet or less or a studio, units within half a mile walking distance of public transit, units in a historic preservation district, and units that are part of the existing primary residence or an existing accessory structure.

A junior ADU needs no additional parking. These exemptions mean most Santa Rosa ADUs do not need new parking, but confirm which exemption you rely on in writing.

Hillside and creekside lots

Extra rules apply in sensitive areas. On hillside lots, an ADU that exceeds the one-story height limit or 800 square feet must observe 15-foot side and rear setbacks, while smaller compliant units keep the four-foot standard.

Along creeks, an ADU over 16 feet tall or 800 square feet must meet the creekside setbacks in Section 20-30.040, and smaller units keep four feet. Santa Rosa also has resilient-city provisions for units in fire-prone areas that the city applies in specific circumstances, so check whether your parcel is flagged.

Junior ADUs

A junior ADU is limited to 500 square feet of habitable space and must have its own efficiency kitchen with a cooking appliance and counter and storage of reasonable size. Only one is allowed per parcel. Tiny homes on wheels are treated separately and are not governed by the ADU section, with their own setbacks, a 10 percent slope limit and other rules.

Permits, fire and school fees

The city’s ADU requirements and application checklist explains what to submit with a building permit: architectural, structural, grading, landscape and irrigation plans, plumbing, electrical and mechanical plans, and proof that other agency permits and fees are paid. A soils engineer’s letter may be required for some properties.

The Fire Department may require added measures if any part of the ADU is more than 150 feet from fire department access or 400 feet from a water supply, particularly for units over a garage or carport.

The checklist also flags school fees for ADUs over 500 square feet through Santa Rosa City School District at 707-890-3800 ext. 80214, and it includes a path for legalizing an existing unit. See our Santa Rosa building permits guide for the permit side.

Zoning and selling a Santa Rosa house

Zoning compliance affects value and financing. A legal ADU can raise a home’s value and rental income, while an unpermitted unit may not be counted by appraisers or lenders and can force a price cut. If the city cites the unit, see the Santa Rosa code enforcement guide. Our statewide guide to selling as-is with unpermitted work explains disclosure duties. Before listing, work through this checklist:

Identify every unit, conversion or addition and whether it was permitted.
Compare each against the setback, size, height and parking standards above.
Check whether the parcel sits in a hillside, creekside or fire-prone overlay.
Ask the city what legalizing would require and cost.
Compare that to selling as-is for cash.

How to sell a house in Santa Rosa

Identify any unit or addition that lacks a permit or fails current standards.
Gather permits, plans and city correspondence.
Request a no-obligation cash offer for the house as it stands.
Choose your closing date.
Close with no legalization or repairs required.

Related Santa Rosa pages: selling as-is, selling fast and the cash offer process.

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Frequently asked questions

How many ADUs can a Santa Rosa lot have?

On a single-family lot, up to two ADUs and one junior ADU, per Section 20-42.130.

What are the setbacks for a new ADU in Santa Rosa?

Four feet from the side and rear lines for new attached or detached units, five feet above a garage, and eight feet on a side-corner.

How big can a detached ADU be?

Up to 1,200 square feet of habitable space. A junior ADU is capped at 500 square feet.

Does a Santa Rosa ADU need parking?

One space is the baseline, but units of 750 square feet or less, studios, units near transit, in historic districts or within existing buildings are exempt.

How tall can a Santa Rosa ADU be?

16 feet for one story, 18 feet near major transit, 25 feet if attached, and never more than 27 feet.

Can I sell a Santa Rosa home with an unpermitted unit?

Yes. Disclose it and sell as-is, including to a cash buyer.

More guides

Sources

This guide is general information from public sources, not legal advice. Confirm current rules with the city.