TLDR

San Diego is one of the most ADU-friendly cities in California, but the rules changed meaningfully in 2025. Here's the short version:

State law guarantees every single-family lot the right to at least one ADU plus one JADU, with an 800 sq ft minimum buildable, 4-foot side/rear setbacks, and no minimum lot size.
San Diego City's ADU Bonus Program (which once allowed unlimited units) was capped in 2025 — now 4 to 6 total units depending on lot size, and eliminated in eight low-density RS zones effective August 22, 2025.
Permitting is ministerial: the city must decide within 60 days (30 days for pre-approved plans).
No impact fees on ADUs under 750 sq ft.
As of 2025, you can now sell certain ADUs separately as condos.

This guide breaks down every rule, with official sources. Always confirm specifics with the City — ADU law shifts constantly, and the Coastal Zone has its own pending timeline.

Important: This article is educational, not legal or permitting advice. ADU regulations change frequently. Verify current requirements with the City of San Diego Development Services Department and California HCD before you build.

What Is an ADU (and a JADU)?

An Accessory Dwelling Unit (ADU) is a self-contained second home on a residential lot — its own kitchen, bathroom, sleeping area, and entrance. San Diegans call them granny flats, in-law suites, casitas, or backyard cottages. There are three main types:

Detached ADU — a standalone structure separate from the main house (the classic backyard cottage).
Attached ADU — built onto the existing home as an addition.
Conversion ADU — created inside existing space like a garage, basement, or part of the house.

A Junior ADU (JADU) is a smaller unit — up to 500 sq ft — carved out of the existing walls of a single-family home. It can share a bathroom with the main house and must have an efficiency kitchen and a separate entrance.

The Two Layers of San Diego ADU Rules

This is the part that confuses most homeowners. There are two sets of rules stacked on top of each other:

California state law — the baseline rights that apply everywhere, including San Diego. Cities cannot take these away.
San Diego City rules — including the local ADU ordinance and the ADU Bonus Program, which can grant more than the state minimum (but was significantly tightened in 2025).

We'll cover both.

Layer 1: California State Law (Your Baseline Rights)

These apply to every single-family lot in San Diego, no matter what local zoning says.

Lot Size

There is no minimum lot size requirement for an ADU under state law. If you have a single-family home, you can build an ADU regardless of how small your lot is.

How Many Units

Every single-family parcel is entitled to at least one ADU and one JADU. In practice, the common state baseline is one detached/attached ADU + one JADU per single-family lot. Multifamily properties get additional allowances (more below).

Size Limits

ADU Type	Maximum Size
Detached ADU	Up to 1,200 sq ft
Attached ADU	Up to 1,200 sq ft (or 50% of the main home's floor area, whichever is less)
Garage / structure conversion	The existing footprint (no size cap imposed)
JADU	500 sq ft of interior livable space
State-guaranteed minimum	You can always build at least 800 sq ft if you meet 4-ft setbacks

Setbacks

4 feet minimum on side and rear yards for detached ADUs.
Conversions keep existing setbacks — even if less than 4 feet.
The front setback cannot block an ADU of 800 sq ft or less.

Height

Detached ADUs must generally be allowed up to 16 feet, and 18 feet in many cases (such as near transit or for two-story designs). San Diego's local rules now cap detached ADUs at 2 stories.

Parking

No parking is required when the ADU is:

Within ½ mile walking distance of public transit
A garage or existing-structure conversion
In a historic district
Within one block of a car-share vehicle

When parking can be required, it's capped at one space per ADU.

Owner Occupancy

Standard ADUs: no owner-occupancy requirement. You can rent out both the main house and the ADU.
JADUs: Owner occupancy can only be required if the JADU shares a bathroom with the main home. As of January 1, 2026 (AB 1154), a JADU with its own separate bathroom is exempt from the owner-occupancy requirement.

Permitting Timeline (State-Mandated)

Step	Deadline
Completeness determination	15 business days
Full approval or denial	60 days
Using a pre-approved plan set	30 days

If the city misses the 15-day completeness deadline, your application is automatically deemed complete.

Impact Fees

No impact fees on ADUs under 750 sq ft.
Larger ADUs must have fees proportional to the main home's size.
ADUs/JADUs under 500 sq ft are also exempt from school impact fees.

Short-Term Rentals

JADUs (and many ADUs) require a 30-day minimum rental term under state law — you generally cannot Airbnb a JADU.

Layer 2: San Diego City's ADU Bonus Program (Major 2025 Changes)

Here's where San Diego stood out — and where the biggest recent changes happened.

What the Bonus Program Was

San Diego's ADU Bonus Program let homeowners build extra market-rate ADUs in exchange for building deed-restricted affordable ADUs, especially inside Transit Priority Areas (TPAs). Originally there was no cap, which led to a handful of single-family lots sprouting a dozen or more units — and a major public and state-level backlash.

The 2025 Reforms (Effective August 22, 2025)

On June 16, 2025, the City Council voted 5–4 to scale the program back. The changes took effect August 22, 2025. Key points:

1. Hard cap on total units per lot (brand new):

Lot Size	Max ADUs/JADUs Total
Up to 8,000 sq ft	4
8,001 – 10,000 sq ft	5
10,001 sq ft or more	6

2. Bonus Program eliminated in eight low-density zones: RS-1-1, RS-1-2, RS-1-3, RS-1-4, RS-1-8, RS-1-9, RS-1-10, and RS-1-11 — unless the area is a High/Highest CTCAC Opportunity Area. The Bonus Program remains in other residential and multifamily zones.

3. Standard (non-bonus) single-family allowance: one conversion ADU + one detached ADU + one JADU.

4. Bonus formula inside TPAs: one bonus market-rate ADU for each affordable (very-low, low, or moderate income, deed-restricted 15 years) ADU.

5. Fire safety: Lots in High/Very High Fire Hazard Severity Zones on cul-de-sacs or single-access roads are ineligible for the Bonus Program. All Bonus ADUs require fire sprinklers, and 4-foot setbacks apply to all ADUs in high-fire zones.

6. Parking: One off-street space per Affordable/Bonus ADU outside a TPA; exempt inside a TPA.

7. Height: Detached ADUs limited to 2 stories.

8. Community Enhancement Fee: New fee on ADUs under 750 sq ft to fund local infrastructure (waived for deed-restricted low-income units in top CTCAC zones).

9. Compliance penalties: Fines for violating affordable-rent deed restrictions rise to a minimum

0,000 per ADU per month.

Coastal Zone Caveat

If your property is in the Coastal Zone (much of the area west of I-5 — La Jolla, Pacific Beach, Ocean Beach, Point Loma, parts of the beaches), these local changes require California Coastal Commission certification, anticipated in 2026. Confirm the effective rules for your specific parcel before applying.

Can You Sell an ADU Separately Now?

Yes — this is one of the biggest recent shifts. As of the 2025 reforms (building on state law AB 1033), San Diego allows homeowners to sell ADUs separately as condominiums. Important exception: ADUs created through the ADU Bonus/Density Bonus Program are NOT eligible for separate sale. This opens real possibilities for homeowners who want to build, then sell a unit to recoup costs.

What Does It Actually Cost to Build an ADU in San Diego?

Costs vary widely by type, size, and finishes, but here are realistic 2026 San Diego ranges:

ADU Type	Typical Cost Range
Garage conversion	$80,000 – 80,000
JADU (interior conversion)	$60,000 – 30,000
Detached ADU (new build, ~600–800 sq ft)	50,000 – $450,000+
Attached ADU addition	00,000 – $400,000

Add soft costs: architectural/design (

0K–$30K), permits and city fees, utility connections, and site work. Detached ADUs in San Diego frequently land around $400–$550 per square foot all-in.

Financing Help

The San Diego Housing Commission (SDHC) ADU Finance Program offers qualifying lower-income homeowners a construction loan up to

50,000 plus free technical assistance. See sdhc.org.

Realistic Timeline From Idea to Move-In

State law sets the city review clock, but the full project takes longer:

Phase	Typical Duration
Design & plans	1 – 3 months
City permit review (state-mandated)	Up to 60 days (30 with pre-approved plans)
Construction (detached new build)	4 – 8 months
Conversion (garage/interior)	2 – 4 months
Total (detached, realistic)	8 – 14 months

Using the City's pre-approved (standard) plan sets can shave weeks off both design and review.

How an ADU Affects Selling Your San Diego Home

ADUs are increasingly valuable, but they also add complexity when you sell:

An owned, permitted ADU typically adds value and rental income appeal.
Unpermitted ADUs or conversions are a common deal-killer — appraisers and lenders may not count the square footage, and buyers worry about legalization costs. (San Diego has had amnesty-style programs to legalize older units; check current status.)
Tenant-occupied ADUs add the same complications as any rental — see our tenant-occupied property guide.
A half-finished ADU project can scare off traditional buyers entirely.

If you've got an unpermitted granny flat, a stalled ADU build, or a property where the ADU situation is complicating a sale, that's exactly the kind of thing we handle. We buy homes as-is, permitted ADU or not.

Frequently Asked Questions

Do I need a minimum lot size to build an ADU in San Diego?

No. California state law removed minimum lot size requirements for ADUs. If you own a single-family home, you can build at least one ADU regardless of lot size, subject to setbacks and building codes.

How many ADUs can I build on my San Diego lot?

Under state baseline rules, one ADU plus one JADU on a single-family lot. Under San Diego's Bonus Program (where still available), 4 to 6 total units depending on lot size as of the August 2025 reforms — but the program was eliminated in eight low-density RS zones. Multifamily lots have separate, higher allowances.

How long does ADU approval take in San Diego?

The city must approve or deny a complete application within 60 days (30 days if you use a pre-approved plan set). Completeness must be determined within 15 business days, or the application is automatically deemed complete.

Do I have to live on the property to rent out my ADU?

For standard ADUs, no — California removed the owner-occupancy requirement. For JADUs, owner occupancy can be required only if the JADU shares a bathroom with the main home; as of January 1, 2026, a JADU with a separate bathroom is exempt.

Are there impact fees on ADUs?

No impact fees apply to ADUs under 750 sq ft or JADUs under 500 sq ft. Larger ADUs have fees proportional to the primary home. San Diego also added a Community Enhancement Fee on smaller bonus-program units.

Can I sell my ADU separately from my house?

In many cases yes, as a condominium, following 2025 reforms and state AB 1033 — but ADUs built through the ADU Bonus/Density Bonus Program are not eligible for separate sale. Confirm your specific situation with the City.

Can I short-term rent (Airbnb) my ADU or JADU?

JADUs require a 30-day minimum rental term under state law, so traditional short-term rentals are prohibited. ADU short-term rental rules are governed by San Diego's separate STR ordinance — check current STR license rules before counting on Airbnb income.

What if my property is in the Coastal Zone?

The 2025 local reforms require California Coastal Commission certification for Coastal Zone properties, anticipated in 2026. If you're west of I-5 in areas like La Jolla, PB, OB, or Point Loma, confirm exactly which rules apply to your parcel before applying.

My ADU isn't permitted. Can I still sell my house?

Yes. You can sell as-is to a cash buyer who understands unpermitted units, or pursue legalization first. Unpermitted ADUs often reduce your traditional buyer pool, which is where cash buyers like us come in.

Official Resources

Always verify current rules directly:

Thinking About Selling Instead of Building?

ADUs are a great wealth-building tool, but they're not the right move for everyone. Building one takes 8–14 months, a large upfront investment, and a tolerance for construction and city processes. Some homeowners look at the cost, timeline, and hassle and decide they'd rather just sell and move on.

If you own a San Diego property with an existing ADU (permitted or not), a stalled ADU project, or land where building one isn't realistic for you, we'd be glad to take a look. We buy homes as-is, in any condition, ADU situations included, and close in 7–21 days with no commissions or repairs.

Get a no-obligation cash offer or call us directly. We're local to San Diego, we know the ADU landscape, and we're happy to talk through your options — even if building (or staying put) turns out to be the better path for you.