San Diego ADU Laws: Size, Parking, and Bonus Program

San Diego ADU laws let you add an accessory dwelling unit on nearly any residential lot in the city, with rules drawn from both California Government Code and the San Diego Municipal Code. On a single-family lot you can generally build one detached ADU, convert existing space like a garage into a second ADU, and add a junior ADU inside the main house. Size tops out at 1,200 square feet for a new unit, parking requirements are waived in most of the city, and approval runs through a staff-level process with no public hearing. The details below cover what you can build, where, and how to get it permitted.

How Many Units You Can Add Per Lot

On a single-family lot, the baseline is one detached ADU plus a conversion ADU (such as a garage conversion) plus one JADU inside the primary home. That’s up to three accessory units in addition to the main house, though no lot may exceed four total dwelling units under SB 9 rules.¹

Multifamily properties follow different math. You can convert existing non-livable space into ADUs equal to 25 percent of your existing units (at minimum one), plus build up to two detached ADUs on the lot. On properties with existing multifamily buildings, up to eight detached ADUs may be allowed if the number doesn’t exceed the existing unit count.¹ JADUs are not available on multifamily lots because they must be built inside a single-family residence.

Which Properties Qualify

ADU regulations live in San Diego Municipal Code Section 141.0302. Residential zones such as RS (Residential Single Unit) and RM (Residential Multiple Unit) allow ADU construction as a limited use decided through Process One, a staff-level approval with no public hearing.² Mixed-use and commercial zones that permit residential development, including the CC (Commercial-Community) designation, also qualify.

Transit Priority Areas (TPAs) get favorable treatment. These are parcels within one-half mile of a major existing or planned transit stop, and properties inside them see higher height limits, broader parking exemptions, and eligibility for the city’s Bonus ADU program. The city publishes a downloadable TPA map so you can check your address before you design anything.³

Coastal Overlay Zone Properties

Building an ADU within San Diego’s Coastal Overlay Zone adds a layer of permitting. Unless the unit is fully contained inside the existing primary structure with no increase in habitable area, a Coastal Development Permit is required on top of the standard building permit.⁴ In the non-appealable area of the Coastal Zone, the city can issue the CDP administratively through Process One if certain findings are met, and that decision cannot be appealed to the California Coastal Commission.

Parking in the Coastal Zone works slightly differently. No space is required unless the property sits within the Beach Impact Area of the Parking Impact Overlay Zone and outside a TPA. Even then, only one space is required, and exemptions still apply for units under 500 square feet, attached units, and properties in a residential permit parking district.⁴ Projects creating enough total dwelling units to hit the inclusionary housing threshold (five or more units in the Coastal Zone, versus ten elsewhere) also trigger affordable housing obligations.

Size Limits

The maximum floor area for any attached or detached ADU in San Diego is 1,200 square feet, with a minimum of 150 square feet.² A JADU is capped at 500 square feet of interior livable space.¹

For attached ADUs, the city can cap your unit at 50 percent of the existing primary home’s floor area, but that cap cannot push your allowable size below 850 square feet for a studio or one-bedroom, or below 1,000 square feet for a two-bedroom.¹ So if your main house is 1,200 square feet, the 50-percent calculation yields 600 square feet, but you’re still entitled to build an 850-square-foot one-bedroom ADU.

ADUs built within an existing structure, whether inside the primary home or inside an accessory building like a garage, have no maximum size requirement under the municipal code. You can add up to 150 square feet beyond the existing footprint solely for a new entrance.² These measurements cover habitable space and exclude garages, porches, and similar non-habitable areas.

Height and Setbacks

Detached ADUs on single-family lots cannot exceed two stories and must stay within the maximum structure height of the underlying base zone.⁴ A standard one-story detached ADU is generally allowed up to 16 feet under state law. That ceiling rises to 18 feet inside a Transit Priority Area and can reach 25 feet for ADUs attached to or built above an existing garage, depending on the base zone’s height limit.

New detached ADUs require a minimum four-foot setback from side and rear lot lines. For ADUs taller than 16 feet sitting next to a residential use, the base zone’s setback rules may apply instead if those setbacks are actually smaller than four feet.⁴

Converting an existing permitted structure like a garage or shed into an ADU is where the rules get noticeably more flexible. No additional setback, height, lot coverage, or floor area requirements apply beyond fire safety provisions.⁵ That’s a major advantage for homeowners with tight lots and an old garage sitting on the property line.

Every ADU must have its own independent exterior entrance separate from the primary house. Attached units follow the same building height and setback rules as the primary residence, and front setbacks must match whatever applies to the main house.⁴

Parking, Solar, and Fire Sprinklers

San Diego eliminates parking requirements for ADUs in most situations. No additional parking is required if the property is within a half-mile of public transit, inside a historic district, or if the ADU is a conversion of an existing structure, a studio unit, or attached to the primary home. Demolished or converted garages do not trigger replacement parking either.⁴ The transit and conversion exemptions alone cover most San Diego ADU projects, so budgeting for a new parking space is rarely necessary.

Newly constructed detached ADUs must include solar photovoltaic panels under California’s Title 24 energy standards. Conversions of existing structures have different requirements and may qualify for exceptions, and you can add new panels to an existing rooftop system rather than installing a separate array.⁶

Fire sprinklers are only required inside your ADU if the primary residence already has a sprinkler system. If your main house doesn’t have sprinklers, the city cannot mandate them for the accessory unit.⁷

Owner-Occupancy and Rental Rules

California law prohibits local agencies from requiring owner-occupancy for ADUs, so you don’t have to live on the property to rent out an ADU.¹ JADUs work differently. If a JADU shares sanitation facilities with the main house, the owner must live on-site in the primary dwelling, the ADU, or the JADU. If the JADU has its own bathroom, no owner-occupancy is required.⁴

Before pulling a building permit for a JADU, you’ll need to record a Junior Unit Agreement stating that neither the main house nor the JADU may be sold separately and that the owner will reside in one of the units.⁴

Short-term rentals are off the table for nearly all ADUs in San Diego. Any ADU permitted after September 2017 cannot be rented for fewer than 30 days, and California state law reinforces the prohibition. Code enforcement issues civil penalties of $1,000 per day per violation when ADUs are found listed on platforms like Airbnb, and enforcement continues until the host cancels the license and all bookings. Only about 100 ADUs permitted before the 2017 cutoff are legally eligible for short-term rental use.

The Bonus ADU Program

San Diego’s Bonus ADU program lets property owners build additional market-rate units in exchange for providing deed-restricted affordable ones. Within Transit Priority Areas, you earn one bonus ADU for every affordable unit you build, with no cap on the total. Outside TPAs, you still get one bonus unit per affordable unit, but no additional bonuses beyond that.⁸

You choose the income tier for your deed-restricted units, and the restriction length varies. Moderate-income units carry a 15-year affordability restriction. Low-income and very low-income units carry a 10-year restriction. Moderate-income tenants whose earnings eventually exceed 140 percent of the area median income must be given 180 days’ notice to vacate, while very low- and low-income tenants whose income rises are allowed to move into the next tier rather than being displaced immediately.⁹

The Permit Process

Your application package starts with a site plan showing lot boundaries, existing structures, and the proposed ADU location. You’ll also need floor plans with room dimensions and fixtures, elevation drawings covering all four sides, and structural calculations for seismic and wind loads. Proof of ownership (title report or grant deed) is required before the city will process anything. Forms come from the San Diego Development Services Department. Incomplete applications get bounced before review begins, so getting the package right the first time is the single most effective way to avoid delays.

Applications go through the city’s online portal for initial screening, which runs two to four weeks. After screening, you pay plan check fees and the application enters formal departmental review covering safety, zoning, and environmental compliance.

This is where most projects burn time. California law requires cities to approve or deny ADU applications within 60 days, but San Diego frequently extends timelines for health and safety review. Each review cycle takes roughly three to six weeks, and the average project goes through three to four cycles of corrections before all departments sign off. You get 30 days to respond to each correction notice; miss that window and you start over with a new submittal.

Plan on three to six months for permitting alone, with complex projects running longer. Once the permit issues, construction proceeds through milestone inspections for foundation, framing, plumbing and electrical rough-in, and a final inspection that verifies the finished work matches the approved plans. Passing final inspection produces a certificate of occupancy allowing the unit to be inhabited.

Construction Costs and Impact Fees

San Diego ADU construction typically runs $335 to $425 per square foot for projects of 600 square feet or more, which puts a standard 800-square-foot detached unit somewhere between $268,000 and $340,000 before permit fees and soft costs. Smaller units and conversions tend to cost less per square foot, though per-unit savings can be offset by fixed costs like utility connections, solar panels, and plan preparation.

Development impact fees follow a tiered structure under state law. ADUs with 750 square feet or less of livable space are completely exempt, as are all JADUs under 500 square feet. ADUs larger than 750 square feet are subject to impact fees, but those fees must be proportional to the square footage of the primary dwelling rather than charged at the full rate.¹ The proportional calculation is a significant reduction compared to the fee for a stand-alone home of the same size.

HOA Restrictions

California law prevents homeowners associations from blocking ADU construction outright. Under Civil Code Section 4751, any CC&Rs that effectively prohibit or unreasonably restrict construction or use of an ADU or JADU are void and unenforceable. An HOA can impose reasonable aesthetic standards like exterior materials and architectural style, but those standards cannot make it impossible to build an ADU that otherwise complies with local and state law.

Can You Sell an ADU Separately?

California’s AB 1033 authorizes local jurisdictions to adopt ordinances allowing the separate sale of an ADU as a condominium, independent from the primary residence. This is not automatic. The local agency must first adopt such an ordinance, and the property must go through a condominium conversion process including a tentative map, a condominium plan prepared by a licensed surveyor or civil engineer, written consent from any existing lienholder, and HOA authorization if applicable.¹⁰ Check the current status of local adoption before relying on a future separate sale as part of your investment plan.

1
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook March 2026
2
City of San Diego. San Diego Municipal Code Chapter 14, Article 1, Division 3 – Residential Use Category – Separately Regulated Uses
3
City of San Diego. Transit Priority Areas per SB 743
4
City of San Diego. Accessory Dwelling Unit/Junior Accessory Dwelling Unit
5
County of San Diego, Planning and Development Services. Accessory Dwelling Unit and Junior Accessory Dwelling Unit
6
California Energy Commission. 2022 Energy Code Accessory Dwelling Units (ADU) FAQs
7
California Department of Housing and Community Development. Review of San Diego’s Accessory Dwelling Unit (ADU) Ordinance under State ADU Law
8
City of San Diego. Accessory Dwelling Units
9
San Diego Housing Commission. ADU Bonus Program Quick Facts
10
County of San Diego, Planning and Development Services. Separate Sale of ADUs as Condominiums Qualifications Guidance