Garage Conversion to ADU: What It Really Costs in San Diego

By Cali Dream Construction | September 22, 2026 | San Diego

Converting a garage into an accessory dwelling unit (ADU) is one of the most popular ways to add a rental or a place for family in San Diego — and for good reason. The footprint already exists, the structure is often already permitted, and California state law has made garage conversions far easier to approve. But “easier” is not the same as “cheap,” and the real cost depends on what condition your garage is in today.

Why Garage Conversions Are Popular in San Diego

State ADU laws (California Government Code 65852.2 and related bills) require most local agencies to approve ADUs that meet basic standards, and they cap or waive certain impact fees for ADUs under a set size. San Diego, like most of the county, has updated its rules to match. The result is that converting an existing garage is now one of the fastest paths to a legal second unit — no setback headaches, no new foundation from scratch.

Garage conversions also work especially well in older neighborhoods with detached garages in the back, common in areas like North Park, Normal Heights, Clairemont, and City Heights, where the alley-loaded lots already orient the garage toward the rear yard.

The Real Cost Range

For a typical two-car garage (roughly 400 square feet), expect a full conversion to land somewhere in the range of $80,000 to $160,000 in San Diego, with more modest finish packages at the low end and higher-end or structurally complicated jobs at the top. Smaller one-car garages can come in lower; jobs that require a new slab, extensive foundation work, or a full seismic upgrade will run higher.

Here is where the money typically goes:

• Foundation and slab work: many garages have a slab that is too thin or lacks proper moisture protection, so pouring or reinforcing is common.
• Raising the ceiling and roof: garage ceilings are often too low for habitable space, which means reframing or adding roof structure.
• Insulation, drywall, and finishes: a garage is not built to be lived in, so you are effectively building interior walls from scratch.
• Plumbing: adding a bathroom and kitchenette means tying into or extending water and sewer lines, which is often the single biggest cost driver.
• Electrical and HVAC: a separate panel or upgraded service, plus heating for the unit.
• The garage door: replacing it with a wall, window, or French doors — and handling the curb-cut and driveway considerations.

Permit Fees and Process

In the City of San Diego, you file through the Development Services Department. Plan check and permit fees for an ADU conversion commonly run in the low thousands of dollars, though the exact number depends on the project valuation and whether any impact or school fees apply. County unincorporated areas go through County Planning & Development Services, and North County cities like Encinitas, Carlsbad, and Escondido have their own building divisions with their own fee schedules.

A licensed contractor will handle the plans, the permit, and the sequence of inspections (foundation, rough framing, plumbing, electrical, insulation, final). This is not a project to rush — a botched conversion can end up unpermitted, which becomes a problem at refinance or sale.

Garage Conversion vs. Detached ADU

A conversion usually costs less per square foot than a new detached ADU because the shell already stands, but the savings are not as large as people expect once you account for the structural and utility work a garage needs. A new detached ADU gives you a clean layout and a brand-new envelope, at a higher total cost. The right choice depends on your lot, your budget, and whether you want to keep any parking.

One thing to plan for: state law allows cities to require replacement parking when you convert a garage in some cases, or you may need to add on-site parking. Discuss this early so there are no surprises.

Financing and Return

Many homeowners fund conversions through a home equity line of credit, a cash-out refinance, or a renovation loan. The return shows up two ways: rental income from a legal unit, and added value when you sell. San Diego rents for a clean one-bedroom ADU remain strong, which is why so many owners treat the unit as an income asset, not just an extra room.

Be realistic about the timeline. A straightforward conversion might take three to five months; one with significant structural work can stretch longer. A written agreement and a clear scope keep everyone aligned.

How Cali Dream Approaches It

We’re an owner-led general contractor, which means you work directly with the person responsible for the build rather than a rotating cast of project managers. We start with an initial project review of your garage — slab, roof, utilities, lot access — and give you an honest, itemized sense of what a conversion would cost and what trade-offs you’d be making. No vague promises, just a straight read on your property.