ADU rules for
the County

On a typical single-family lot in County of San Diego, current state law lets you stack up to four units beyond the house, and yes, that's by right (no neighborhood vote, no public hearing).

• 1 standard ADU, detached or attached. Up to 1,200 sf detached (matches state max).
• 1 extra detached ADU, up to 800 sf, on top of the standard one.
• 1 conversion ADU, turn an existing garage, basement, or accessory structure into a unit.
• 1 Junior ADU (JADU), up to 500 sf, carved out of the primary home with its own entrance.

Most people build one. But knowing the stack exists matters, it changes how you plan a property if you're thinking about family, rental income, or future flexibility.

On multifamily lots the math gets even better: up to 8 detached ADUs, plus non-livable space conversions. Ask us about it on a Discovery Call.

Setbacks (the gap between your ADU and the property line): 4 ft on the sides and rear in County of San Diego. The front setback follows whatever your underlying zone requires (usually 15–20 ft).

Height: 16 – 25 ft. Two-story ADUs allowed; subject to zone-by-zone maxes.

Parking: 1 space. Here's the part most homeowners don't realize, California waives the parking requirement entirely if any of these apply to your lot:

• You're within a ½-mile of a major transit stop (trolley, BRT, frequent bus).
• You're inside a historic district.
• The ADU is a conversion of an existing garage or attached space.
• You're on a block with on-street permit parking or a car-share within one block.

And since January 2025, if you tear down a garage to build the ADU, the city cannot ask you to replace those parking spaces. We confirm your specific situation during feasibility so you don't give up driveway you don't need to.

County of San Diego follows the California Residential Code, the California Building Code, and Title 24 energy standards, same as the rest of the state. On top of that, here's what tends to actually shape how an ADU looks and where it sits:

• Match the main house. Most cities, including County of San Diego, ask the ADU to use the same roofing, siding, trim, and color palette as the primary residence. It doesn't have to be identical, just visibly related.
• Height & massing. 16 – 25 ft ceiling, with daylight planes and roof-form rules that protect the neighbor's view and light.
• Building separation. Usually 6 ft between the ADU and the main house (eave to eave). Closer than 10 ft and fire-rated construction kicks in.
• In-person plan submittal. The city still requires physical drawings at the counter, we handle the trips.

We design every set to clear plan-check on the first round, no variances, no design exceptions, no surprise corrections from the city.

For a clean, well-coordinated submittal in County of San Diego, plan on roughly 3–5 months from drop-off to permit in hand.

That window includes the city's plan-check rounds plus our turnaround on any corrections. Most ADUs clear plan-check in 1–2 review rounds when the design follows local code from the start (which is the only way we draw).

• Add 2–4 weeks if school-district fees, sewer-availability letters, or utility "will-serve" letters take longer than usual.
• Construction itself usually runs 6–9 months after permit, depending on size, site access, and material lead times.

Total project cost, design, permit fees, and construction, usually lands between $280,000 and $480,000 for a well-built detached ADU in County of San Diego, depending on size, finishes, and site conditions.

City permit fees alone in County of San Diego run about $15–18/sf, this is paid to the city and is separate from school fees, utility hookups, and impact fees.

The big variables (in order of magnitude):

• Size + finish level, biggest single driver. A 600 sf efficiency lands very differently than a 1,200 sf 2-bedroom.
• Utilities, new sewer/water laterals, an electrical panel upgrade, gas service: each one can be $5–20K.
• Site work, slopes, retaining walls, tree removal, soft soils.
• School & impact fees, typically waived for ADUs under 750 sf.

Our Feasibility Study ($1,000, credited back at signing) gives you a real budget for your specific lot, not a guess.

Long-term rental: yes. Every ADU in County of San Diego can be rented to a long-term tenant. This is the most common path, and it's how most ADUs pay for themselves.

Short-term rental (Airbnb / VRBO): mostly no. California state law lets cities ban short-term rentals of ADUs, and most do. Long-term leases of 30+ days are typically the floor.

Selling the ADU separately: yes, under AB1033. County of San Diego has adopted the state law that allows a qualifying ADU to be subdivided and sold as a condo separate from the main house. The rules are still settling, ask us about the current status when we talk.

Owner occupancy is not required on the ADU itself. A JADU does require the owner to live on the lot, in either unit.

Yes, this is one of the most-asked questions. We don't lend, but we partner with San Diego lenders who specialize in ADU construction loans and know how to underwrite future rental income.

The four common paths:

• HELOC / home equity, cheapest money if you have equity in the main house.
• Cash-out refinance, one larger mortgage at today's rates.
• ADU construction loan, draws disbursed at construction milestones, converts to a permanent mortgage at completion. Some lenders count projected rent toward qualifying.
• State / utility programs, CalHFA's ADU Grant, all-electric rebates, SDG&E incentives, water-district credits. We track which are open and help you stack them.

On your Discovery Call, ask for our current intro list, we keep it updated.

Honest answer: the three things that derail ADU projects in County of San Diego are almost always the same. Here's how we head them off.

• Plan-check kickbacks. The city sends corrections, designer takes 2 weeks to respond, resubmits, gets another round, project drags 6+ months. How we prevent it: we design to County of San Diego's checklist from the start and respond to corrections within 48 hours.
• Surprise utilities. Owner finds out at construction the sewer lateral can't handle another unit, or the electrical panel needs upgrading. How we prevent it: we run utility checks during feasibility, before you sign a build contract.
• Scope creep. "Can we add a…" halfway through construction. Each change burns money + time. How we prevent it: we lock the design at permit submittal and bake a small contingency into the budget for the inevitable lot surprises.

None of these are unique to County of San Diego, but how the local desk handles them is. We've been there.