If you’re searching for ADU cost in San Diego County, you deserve a straight answer before you talk to anyone. So here it is: most ADUs in San Diego run between $150,000 and $400,000, depending on the type of unit, the condition of your property, and the finishes you choose.

That’s a wide range, and this post will help you understand exactly where your project is likely to land.

The Three Types of ADUs and What Each One Costs

Not all ADUs are built the same way, and the type you choose is the single biggest factor in your total budget.

Garage Conversion (Most Affordable)

Converting an attached or detached garage into living space is typically the most cost-effective path. You’re working with an existing foundation, existing walls, and an existing roof. The structural work is minimal compared to new construction.

Typical range: $80,000 to $180,000

That range accounts for the wide variation in garage conditions across San Diego County. A clean two-car garage in good shape that just needs insulation, drywall, flooring, a bathroom, and a kitchenette will land on the lower end. A garage with a slab that needs leveling, outdated electrical, or proximity to the property line that requires a fire-rated wall assembly pushes toward the higher end.

Junior ADU (JADU)

A Junior ADU is created inside the existing square footage of your home, usually from a bedroom with a private entrance. State law caps JADUs at 500 square feet. Because you’re not adding square footage to a lot, permit fees are lower and no new utility connections are required.

Typical range: $40,000 to $120,000

JADUs are the most affordable option on paper, but they do require a separate entrance, an efficiency kitchen, and in most cases a shared or dedicated bathroom. The cost depends heavily on where in the house you’re carving out the space and what you’re working with already.

Detached New-Build ADU (Highest Cost)

A freestanding ADU built from the ground up gives you the most flexibility in size (up to 1,200 square feet in most San Diego jurisdictions), layout, and placement. It also carries the highest price tag because you’re starting from scratch: new foundation, new framing, new roof, new utility connections, new everything.

Typical range: $200,000 to $400,000

The upper end of that range reflects ADUs with premium finishes, complex sites (steep slopes, tight access, poor soil), or locations in coastal zones with additional review requirements.

What Drives ADU Costs Up in San Diego

Several factors specific to San Diego County can push your number higher than the averages above.

Site conditions. San Diego’s hillside lots are beautiful, but they cost money to build on. Retaining walls, special foundations, and engineered drainage all add to the bill. A flat lot in Santee is a different conversation than a sloped lot in Escondido.

Utility connections. If your new ADU requires a separate electrical panel, a new water meter, or a sewer lateral upgrade, those costs are real and sometimes significant. The city or county utility department sets those fees, and they’re non-negotiable.

Permit and impact fees. San Diego County jurisdictions each have their own fee schedules. For ADUs under 750 square feet, state law limits certain fees, but above that threshold, school fees, traffic impact fees, and others can add up. This is something we map out specifically for your parcel before you commit to anything.

Finishes. A functional ADU with LVP flooring, stock cabinetry, and builder-grade fixtures is a different budget from a unit with tile floors, custom cabinetry, and quartz countertops. Neither is wrong, it just depends on what you’re using the ADU for.

QUICK TAKE

The fastest way to narrow down your specific cost is a feasibility review. ADUz does this before any design work begins, so you’re not spending money on plans for a project that doesn’t pencil out on your lot.

Breaking Down the Budget Line by Line

Here’s how a typical detached ADU budget in San Diego County might break down:

  • Design and engineering: $8,000 to $20,000
  • City/county permits and fees: $10,000 to $30,000
  • Site work (grading, drainage, utility connections): $10,000 to $40,000
  • Construction (foundation, framing, roofing, MEP): $100,000 to $200,000
  • Finishes (flooring, cabinets, fixtures, appliances): $20,000 to $50,000
  • Landscaping and exterior restoration: $5,000 to $15,000

These numbers overlap with the ranges above because every site is different. A geotechnical report on a hillside lot, for example, is a line item that a flat-lot project never sees.

What ADUz Handles (and Why It Matters for Your Budget)

One of the reasons ADU projects go over budget or stall is the back-and-forth between design, permits, and construction. When those are handled by different teams with no coordination, things fall through the cracks and cost you time and money.

ADUz is a family-owned company based in San Diego County. Alma Sanchez leads the design and permitting side, and her husband David runs The Rock Remodel (CA Lic. 1042918), the licensed build partner who handles construction. The two work together under one roof, which means the drawings your permit is approved on are the same drawings the contractor uses to build.

We’re bilingual, we work across San Diego County jurisdictions, and we’ve designed and permitted ADUs for families who want rental income, space for aging parents, and room for adult kids who aren’t quite ready to move out. We get it because it’s the same conversation we have with our own family.

Ready to Find Out What Your ADU Would Cost?

The best way to get a real number for your property is to talk through it. Call ADUz at (760) 524-1754 for a free ADU consultation. We’ll look at your lot, your goals, and your budget and give you an honest picture of what’s possible.

No pressure, no sales pitch. Just a real conversation from a family that’s been doing this in San Diego County.