Building an ADU in San Diego: rules, setbacks, cost and the grant

The short version

On most single family lots in San Diego you can add up to three units without any special program: one attached or detached ADU up to 1,200 square feet, one ADU converted from existing space such as a garage, and one junior ADU of up to 500 square feet inside the house. The permit is ministerial, the agency has 60 days from a complete application to decide, and a unit under 750 square feet of interior livable space pays no impact fees.

That paragraph is the whole game for most homeowners. The rest of this guide is the detail behind it: how close to the property line you can build, how tall, what the permit path looks like inside the Coastal Zone, what the 2025 reforms changed, what the market is charging in 2026, and the honest status of the state grant, which is closed. Every number here was checked against the city’s Information Bulletin 400 (revised January 2026), the county’s ADU page, the Government Code text and CalHFA’s own page on the day this was written. Rules move every January, so the dates matter.

One thing we will not do in this guide is quote you a price. NewGen bids every project flat after an in-person walkthrough, and an ADU is the last thing anyone should price from a blog post. Where costs appear below, they are published market ranges, attributed to their source.

How many ADUs you can add

In the City of San Diego, a lot with an existing or proposed single family home can have one ADU (attached or detached), one ADU converted from existing space or an existing structure, and one JADU. Multifamily lots can convert up to 25 percent of existing units and add up to eight detached ADUs, never more than the number of existing units.

The three-unit allowance is the part that surprises people. A garage conversion does not use up your detached ADU; it counts as the converted unit, so a detached backyard unit is still on the table, and a JADU carved out of the main house is a third. Whether the lot can physically hold all three is a different question, and it is exactly what the walkthrough answers.

Beyond that sits the ADU Home Density Bonus Program: extra units in exchange for deed restricting units as affordable to very low, low or moderate income households for 15 years. Inside Transit Priority Areas one bonus unit is allowed for each affordable unit; outside them, one bonus unit and one affordable unit total. Since the 2025 reforms the program is capped at 4 total ADUs and JADUs on lots of 8,000 square feet or less, 5 on lots from 8,001 to 10,000, and 6 above 10,000, and it no longer applies in the RS-1 zones (RS-1-1 through RS-1-4 and RS-1-8 through RS-1-11) unless the lot sits in a High or Highest Resource Area. Bonus and affordable units need automatic fire sprinklers and, outside Transit Priority Areas, one parking space each.

Size limits: 1,200 square feet, and an 800 square foot floor

The city caps an attached or detached ADU at 1,200 square feet of gross floor area, with no cap when the unit is converted from existing space. The county caps detached units at 1,200 square feet and attached units at 50 percent of the main house, also up to 1,200. A JADU is 500 square feet at most. State law adds a floor: no local standard can prevent an ADU of at least 800 square feet of interior livable space.

The 800 square foot floor is why setback and lot coverage math rarely kills a project outright. If the zone’s coverage limit would leave you room for 500 square feet, the state rule still guarantees 800. Where it bites is design: an 800 square foot unit with a 16 foot height limit is a one-story footprint, and on a small lot that footprint has to sit somewhere.

The minimum is 150 square feet for either an ADU or a JADU, though nobody builds to it. The practical small unit is a studio around 300 to 400 square feet, which is also comfortably under both fee thresholds covered below.

Setbacks and height

For new construction in the city, an ADU that is 16 feet tall or less can generally be built to the interior side and rear property lines, subject to Building Code fire separation. Taller than 16 feet next to a residential lot, the interior side and rear setback is 4 feet or the zone minimum, whichever is less. In High and Very High Fire Hazard Severity Zones the 4 foot setback applies at any height. The front yard follows the base zone; the street side is the zone requirement or 4 feet, whichever is less. Conversions keep the existing structure’s setbacks.

That zero setback at 16 feet is a city rule, more generous than the state minimum, and it is the reason San Diego backyards can carry a unit that would not fit in many other cities. The trade is fire separation: a wall within 5 feet of the line gets one-hour construction, limited openings, and sometimes no windows on that side. Good design puts the blank wall toward the neighbor and the glass toward the yard.

Height: the city allows two stories for a detached ADU in single family zones, within the base zone’s height limit. The state guarantees at least 16 feet for a detached unit, 18 feet within a half mile walking distance of a major transit stop or on a multifamily lot, and 25 feet or the primary home’s zone limit, whichever is lower, for an attached unit. Two stories buys floor area on a tight lot but gives up the zero setback, since anything over 16 feet moves back to 4 feet.

One more line to check before drawing: lots in fire hazard zones, which include much of Scripps Ranch, Rancho Bernardo, the canyon rims of La Mesa and Poway, and most of the unincorporated county. The 4 foot setback is fixed there, and the 2025 reforms require bonus projects on those lots to sit on an improved public street with two evacuation routes.

Parking

Outside the Coastal Zone the City of San Diego requires no parking for an ADU, and no replacement parking when a garage is converted. Inside the Coastal Zone one space can be required in the Beach Impact Area outside transit priority areas, with exceptions for units of 500 square feet or less, historic districts, attached units, residential permit parking districts and lots within a block of car share. JADUs never require parking.

In practice this means a garage conversion in Clairemont or North Park has no parking question at all, while the same conversion in Ocean Beach or Pacific Beach needs a look at the overlay map first. The unincorporated county still asks for one space per ADU, which can be tandem in the existing driveway.

Permits and the 60 day clock

Every ADU and JADU in the city needs a building permit through Development Services; the city’s own words are “there are no exemptions.” Review is administrative, with no public hearing. Under Government Code section 66317 the agency must tell you within 15 business days whether the application is complete, and must approve or deny a complete application within 60 days, after which it is deemed approved. Pre-approved plans get a 30 day review.

The 60 days start at “complete,” and completeness is where most self-managed projects lose a month. A submittal that is missing the Title 24 energy report, the structural calcs for a two-story unit, or the utility plan showing how sewer reaches the street gets a correction letter, and the clock does not run while you fix it. This is the part of the job our architect owns: the drawing set goes in complete, and the questions that come back are about preferences, not omissions. If you want the general shape of how we run permits on any project, the general contracting page walks through it.

Two overlays change the path. Inside the Coastal Overlay Zone, which covers La Jolla, Coronado, Point Loma, the beach communities and parts of Encinitas and Carlsbad under their own city rules, a Coastal Development Permit is required for any ADU not completely contained inside the existing primary structure. AB 462, signed October 10, 2025, now requires that CDP decision within 60 days as well and removed appeals to the Coastal Commission for ADU permits. And several of the city’s recent ADU ordinances, including the 2025 amendments, are still pending Coastal Commission certification, so inside the Coastal Zone the older rules apply until that lands.

The city also accepts pre-approved plan sets: its own listed providers plus the County of San Diego standard plans, the City of Chula Vista plans and the City of Encinitas permit-ready plans. Using one cuts plan check time and, per the city, halves the plan check fee. The catch is that a pre-approved plan is pre-approved for its own design, not for your lot; siting, utilities and the foundation still get drawn and checked.

What an ADU costs in San Diego in 2026

Two 2026 San Diego cost guides land in the same range: garage conversions at roughly $200 to $400 per square foot (about $80,000 to $200,000 for a two-car garage), and detached new construction at roughly $350 to $550 per square foot (about $200,000 to $420,000 depending on bedrooms and site work). City permit and fee packages run from a few thousand dollars to around $12,000, plus school fees and utility connection charges that can add $10,000 to $25,000 on larger units. Those are market figures, not NewGen quotes.

The number that matters more than the per-foot rate is where the unit sits relative to two fee lines. Under 750 square feet of interior livable space, state law bars all development impact fees, which on a San Diego lot is commonly a five figure saving. At 500 square feet or less, SB 543 (effective January 1, 2026) also removes school impact fees, and it clarified that both thresholds measure interior livable space, not the whole footprint, so a covered porch does not push you over. A 749 square foot one-bedroom and a 760 square foot one-bedroom can be tens of thousands of dollars apart at permit issuance for eleven square feet of room.

Site conditions drive the rest. A detached unit at the back of a deep lot in Escondido or El Cajon may need a long sewer run, an electrical panel upgrade, and a new water meter with its own capacity fees from the Water Authority. A garage conversion on a flat lot in Chula Vista reuses the slab, the walls and often the panel. Same square footage, very different bid, which is why the walkthrough comes before the number.

For the unincorporated county, note that the county’s own trial impact fee waiver ended January 9, 2024; the state 750 square foot exemption still applies there, but the extra county waiver is gone.

The California ADU grant: closed, and what it was

The CalHFA ADU Grant Program is not accepting applications. CalHFA’s page states the latest round was fully allocated on December 28, 2023, and as of September 2026 there is no open application, no waitlist and no announced new round. When open, it reimbursed up to $40,000 per household for pre-development and non-recurring closing costs, for owner occupants within CalHFA income limits.

What it covered is worth knowing in case funding returns: site prep, architectural design, permits, soil tests, impact fees, property surveys and energy reports. It never paid for construction. Eligibility required the owner to live on the property and fall under the county income limit, and investor-owned homes did not qualify.

Two cautions. First, do not build a budget around a grant that does not currently exist; if a new round opens, apply then. Second, CalHFA prints its own warning that anyone who approaches you offering to get you an ADU grant is running a scam. Check calhfa.ca.gov/adu directly.

City versus unincorporated county

Your permit goes to whichever agency has jurisdiction over the lot, and the rules differ. The City of San Diego uses Information Bulletin 400 and Development Services. Lakeside, Ramona, Spring Valley, Alpine, Fallbrook, Valley Center and the rest of the unincorporated area use County Planning & Development Services, which caps detached units at 1,200 square feet, attached units at 50 percent of the main house, keeps a 4 foot side and rear setback with conversions exempt, and asks for one tandem parking space. Every other city in the county, from Carlsbad to Chula Vista, has its own ordinance on top of state law.

The county made one move the city has not: on March 4, 2026 the Board of Supervisors adopted an AB 1033 program, effective April 4, 2026, that lets an ADU in an unincorporated community be sold separately from the main house through a condominium conversion. It is a mapping process, not a simple form, and it does not bypass the tentative map application, but it changes the math for a homeowner who wants to build and eventually sell the back unit. The county also publishes standard ADU plans that are roughly 85 percent complete and need only project-specific information filled in.

Not sure which side of the line you are on? The areas page lists the cities we work in, and the first thing we do on any ADU walkthrough is pull the parcel’s zoning report.

Renting it, living in it, selling it

A standard ADU has no owner occupancy requirement in the city or under state law; the property owner is not required to live on site. Rentals must be 31 consecutive days or longer in the city, and the county requires 30 days. A JADU is stricter: since January 1, 2026 under AB 1154, owner occupancy applies only when the JADU shares a bathroom with the main house, and JADUs may never be used as short term rentals.

The short term rental question comes up on every ADU call, and the answer is simply no. The unit is long term housing by design, which is also why it is treated so generously on fees and parking. What it is very good at is a family member, a long term tenant, or a home office with its own address.

Where ADU projects go wrong

Most ADU delays in San Diego are self inflicted: an incomplete submittal that stops the 60 day clock, a design that crosses the 750 square foot fee line by accident, a sewer or panel problem discovered after framing, or a Coastal Zone lot that nobody checked before drawing.

The fixes are boring and early. Pull the zoning and overlays before the first sketch. Decide the fee line on purpose. Locate the sewer lateral and check panel capacity at the walkthrough, not at rough-in. Draw the fire separation wall on the neighbor side. Submit a complete set once. None of that is clever; it is the difference between a unit that is occupied in eight months and one that is still waiting on corrections at twelve.

If the ADU is part of a larger plan for the property, the same discipline applies to the main house. Our whole-home remodel page covers how we sequence a house and a backyard unit under one schedule.

How NewGen builds one

The architect on our team draws the unit, submits the permit and stays on the job through inspections, and the same crew that framed your neighbor’s kitchen frames the ADU. It starts with a free walkthrough: we look at the lot, the setbacks, the sewer, the panel and the overlays, and we tell you what the parcel actually allows before anyone talks about a number. Then you get one written bid for the scope we agree on. If something changes once the walls are open, you see the cost and approve it before that work moves forward.

Read what we build and how on our ADU page, look at recent work on the work page, or request the walkthrough. We build across San Diego County and into the Temecula and Murrieta corridor, and we will tell you plainly if a lot does not pencil.

Sources checked September 24, 2026: City of San Diego Information Bulletin 400 (rev. January 2026); City of San Diego Regulatory Updates (2025 ADU/JADU amendments effective August 22, 2025); County of San Diego Planning & Development Services ADU page; California Government Code sections 66317 and 66321; SB 543, AB 1154 and AB 462 (2025 to 2026); CalHFA ADU Grant Program page. Market cost ranges from VerifiedADU and CasitaScore San Diego cost guides, both April 2026. This is a builder’s summary, not legal advice; confirm current rules with the permitting agency for your lot.