ADU Construction Process in San Diego

There’s no shortage of interest in ADUs across San Diego, but most homeowners jump in without knowing what the actual ADU construction process really involves. It’s not just about hiring a contractor or drawing up plans. The timeline from idea to move-in spans multiple stages, and each one comes with its own learning curve.

This guide isn’t about selling you a dream unit in your backyard. It’s about helping you understand how to build an ADU in San Diego from start to finish: what happens before a single shovel hits the ground, what slows things down, and what makes a project go from concept to a fully permitted living space.

If you’re still evaluating the financial side of the project, you may also want to read our guide on how much it costs to build an ADU, where we break down the typical expenses involved in planning, permitting, and construction.

Not every San Diego property qualifies for an ADU. Before anything else, you need to understand what your lot allows. That means checking local zoning designations, understanding your lot’s buildable area, and confirming that there’s enough room to meet setback and fire safety rules.

You’d be surprised how many projects stall because the design wasn’t shaped around the site’s actual limits.

If you’re not sure where to start, San Diego’s zoning lookup tool is a helpful first step. Or just call the city’s Development Services Department and ask what your property is zoned for. It might save you weeks of redesigns later.

🔗 Related: San Diego ADU Requirements: What You Need to Know

submitting a good design is essential for a successful project

This is where ideas meet the reality of city code. Whether you’re sketching a detached studio, converting a garage, or adding an above-garage unit, the design needs to check multiple boxes like size, access, fire code, setbacks, and structural integrity.

A good designer or architect can help turn your vision into a layout that’s actually approvable. Expect to go through multiple drafts, especially if you’re working with a tight lot or trying to squeeze in more than just a bedroom and bathroom.

Tip: If you already know the use (guest house, rental, office), make sure the floor plan supports that from the start to save rewrites later in permitting.

Once your design is locked in, it goes to the city for review. In San Diego, that means submitting your full plan set to the Development Services Department (DSD). This includes structural drawings, site plans, Title 24 energy reports, and sometimes soils reports, depending on the project.

The city’s permit review can take anywhere from a few weeks to several months depending on the complexity of your project and how complete your submittal is. JADUs usually move faster since they’re smaller and less intensive. Detached ADUs with new utility runs or grading work tend to take longer.

Most delays happen here, not because of the city, but because the submitted plans don’t meet the code, are missing documents, or make unrealistic assumptions (like putting an ADU 2 inches from the property line without a fire-rated wall assembly).

If you want to keep things moving, respond quickly to plan check comments and don’t try to shortcut the code. San Diego reviewers have seen every trick in the book.

Once your permit is in hand, construction starts. The typical order of operations goes like this:

1. Site Prep & Demo (if needed)

2. Underground utilities: water, sewer, gas, electrical conduit

2. Foundation Work: slab or raised floor

3. Framing & Roof: walls, trusses, sheathing

4. Rough-ins: electrical, plumbing, HVAC

5. Insulation, Drywall, Exterior Finishes

6. Cabinets, Fixtures, Flooring, Paint

7. Final Cleanup & Touch-Ups

Throughout the entire process you’ll have city inspection after every phase is completed, your ADU builder will be the one scheduling and meeting with the inspectors to present them the work and discuss any necessary change if such are required to meet local and national building codes.

weather can cause major delays

Depending on scope and weather, this part of the process usually takes 6-12 months. Garage conversions are often faster. Custom detached units with upgraded finishes or complex utility needs can stretch longer.

Expect the job site to be active 4-5 days a week. There will be noise, dust, subcontractors coming and going, and parking impacts. If you work from home or have pets or young kids, it’s worth planning ahead.

The last part of the process is making sure the finished ADU passes all required inspections. Final sign-off from the city isn’t automatic: your contractor will need to schedule a walk-through with the inspector, who checks that everything was built to code and matches the approved plans.

If something’s off (usually small things at this point like a smoke detector’s missing, or a water heater wasn’t strapped correctly, you’ll get a correction notice and need to address it before approval).

You don’t officially “have” an ADU until the city issues your Certificate of Occupancy. That’s the final green light to move in or rent it out.

Even straightforward ADUs can hit delays. Here are some of the most common ones we’ve seen:

Design changes mid-way

You finalize the plans, submit them, then change your mind about the layout or roofline. That means back to the drawing board and resubmittal, costing weeks.

Incomplete permit submittals

Missing forms, outdated Title 24 reports, or skipping a soils report when required. Each of these kicks the file back to you and restarts the review clock.

Scheduling breakdowns

One trade finishes late, which bumps the next. If the plumber’s behind, the inspector can’t sign off, which means drywall gets pushed, and so on.

Site surprises

Old sewer lines in bad shape. Tree roots where the footing goes. Sloped lots requiring extra retaining or drainage work. These add time and cost fast.

How to avoid most of this?

Start with a realistic design, get a solid permit submittal package, and hire a contractor who manages schedules and trades well. Every step builds on the last and if the early stages are sloppy, everything after tends to get messy.

There’s no one-size-fits-all answer, but most ADU projects in San Diego follow this general timeline:

• Design and planning: 4-8 weeks
• Permit approval: 2-6 months (longer if multiple rounds of corrections are needed)
• Construction: 6-12 months depending on scope
• Final inspections and sign-off: 1-2 weeks

So from start to finish, you’re looking at 10 to 16 months on average, longer if you hit unexpected delays or are building a large, custom unit.

If you’re doing a garage conversion with minimal utility changes, it might wrap up in 4-6 months total. On the other hand, if you’re building a 1,200 sq ft detached ADU on a hillside lot, expect closer to a year and a half by the time everything clears.

Learn more on how long it takes to build an ADU in San Diego

complete detached studio ADU on a slopped lot

You don’t need to figure out the entire ADU construction process on your own. The city’s requirements are specific, and each step, from permits to buildout, can either move quickly or drag on depending on how you plan it.

If you’re not sure where to begin or want help understanding what your lot actually allows, we’re here. Whether you just need guidance or want someone to handle the whole process, we can help you make a smart plan and move forward with confidence.

📞 Call us at (619) 552-2923 or reach out through our short form below.