How Long Does It Take to Build an ADU in San Diego?

If you’re reading this, chances are you’re thinking about adding an accessory dwelling unit (ADU) to your property. But before anything gets built, most homeowners ask the same question: how long does it actually take to build an ADU in San Diego?

The answer depends on several factors, including your lot conditions, design choices, how quickly planning and permitting move along, and the overall scope of the project. For some homeowners, the total ADU construction timeline in San Diego can be as short as four to five months. For others, it stretches past the two-year mark. Same process, different timeline. The difference usually comes down to the details.

Let’s break it down.

Most ADU projects follow three main stages:

• Phase 1: Pre-Planning & Design

• Phase 2: Permitting

• Phase 3: Construction

Your goal? Get through each of those with as few delays as possible. In this article, we’ll walk through what each phase looks like in real life, how long ADU takes to build, and what slows people down, based on real-world experience from San Diego ADU projects.

This is where every ADU project begins: with an idea, some sketchy drawings, maybe a Pinterest board, and eventually a conversation with a contractor, architect, or both.

But before anything gets submitted to the city or drawn up in AutoCAD, you’ll need to make some decisions that directly affect your ADU timeline.

Here’s what this phase includes:

• Initial property research

  What’s your zoning? Are you in a coastal zone? Do you have sewer access? Does your lot allow detached units, or will this be an internal conversion? This is where delays start if you’re unclear.

  read more about ADU requirements in San Diego

• Feasibility & rough planning

  At this point, you (or your team) are figuring out:

  – Where can the ADU physically go on the property?

  – How big can it be based on setbacks, FAR, height limits and ultimately your needs?

  – Will it be detached, attached, over the garage, or a conversion?

• Design development

  Once the general concept is locked in, actual plans are drafted: floor plans, elevations, site plans. This is usually done by an architect, designer, or design-build builder, depending on the complexity.

• Interior planning (optional, but crucial)

  This is where many homeowners stall. Selecting materials, finishes, plumbing fixtures, appliances, tile layouts, all of this can (and should) happen early. If you wait until construction, your project timeline will suffer.

Pro tip: Don’t get lost in the sauce. You might love five different layouts and ten finish combos, but you only need one solid plan to move forward. If you’re not careful, you’ll end up stuck in months of back-and-forth and decision fatigue, which can delay your ADU construction timeline in San Diego and drive up out-of-pocket costs.

• Fast track: 3 to 4 weeks (small, simple project, prepared homeowner)

• Typical: 6 to 10 weeks (most clients, especially if there’s back-and-forth on layout or design)

• Long: 3+ months (coastal properties, indecisiveness, zoning issues, or drawn-out finish selections)

Detached Accessory Dwelling Unit 500 square feet framing

Deciding to Move Forward

You start doing your homework. You meet with a few architects, ask coworkers for contractor referrals, maybe even post your info on Angie’s List. After several meetings and weighing your options, you choose a local ADU builder that feels like the right fit and offers both construction and design services.

That’s a big step forward.

(This stage alone can take people months, sometimes even years, before they finally commit. Don’t worry if it’s taking you a while)

Kicking Off the Design Process

Let’s assume you signed your contract on January 1st, 2025.

That same week, the architect or draftsman schedules a site visit to take measurements and gather initial details. Then they begin drafting the first version of your site plan using tools like AutoCAD, Revit, or Chief Architect.

This first draft usually takes 1 to 2 weeks to complete.

Reviewing and Revising the Layout

Once that initial version is ready, you’ll get it by email. You take a few days to review it with your family (maybe your parents want the bedroom shifted, or you want more space in the kitchen).

You send back your comments, and the designer makes those changes in 2 to 3 days.

Once you’re happy, you approve the design and give the green light.

Turning Layout Into Full Construction Documents

Next, the design team expands your approved layout into a full set of construction drawings. These will include elevation views, cross-sections, code notes, and other technical documents the city requires for permitting.

At this point, things start to slow down. Most ADU plans must go through:

• A licensed structural engineer, who adds the structural components (takes 2–6 weeks)

• A Title 24 energy consultant, who runs calculations and reports (often done in parallel)

Meanwhile, your designer may need another 1 to 1.5 weeks to assemble the full submittal set.

When Are You Ready to Submit?

Even in a smooth, best-case scenario, you’re likely not submitting your ADU plans to the city until early March, a full 2 months after you signed the contract. This early phase plays a major role in determining your overall ADU construction timeline in San Diego.

Rule of thumb: always expect delays, but this gives you a realistic benchmark if you’re trying to figure out how long does it take to build an ADU in San Diego.

This is the part no homeowner wants to deal with but has to. You’ve made it through planning and design, your floor plans are finalized, and your structural engineer signed off. Now it’s time to submit your packet to the city and get those plans approved.

But submitting doesn’t mean you’re close to building. It just means you’re entering the next waiting room.

Here’s what this phase includes:

Plan Submittal

Your designer or builder (or both) will package up your plans into a digital submission, usually through an online portal like Accela. You’ll get a plan check number (usually the same as your assigned permit number), which means the city has received your project. This doesn’t mean anyone has looked at it yet.

Depending on the jurisdiction, you might be in line for 3–4 weeks before anything is reviewed.

First Round of Plan Review

The city assigns your project to a plan checker. Their job is to make sure everything complies: zoning, fire setbacks, structural safety, Title 24 energy reports, and more.

This usually takes 1 to 2 weeks before they respond with either a list of corrections or, in rare cases, a green light.

Corrections and Resubmittals

Almost every ADU submission gets comments back. These are normal and not necessarily bad. They might ask for clarity on property lines, grading info, structural connections, or to correct minor inconsistencies.

This is where delays can stack up:

• Your design team needs to review and revise the plans (1 to 2 weeks depending on how fast you respond)

• The city takes another 2 to 4 weeks to review your resubmission

• If additional corrections come back, the cycle repeats

• Fast track: 6 to 8 weeks (simple project, quick responses, no corrections)

• Typical: 10 to 14 weeks (most projects, at least one correction round)

• Long: 3+ months (complex design that requires additional red tape with clearances from various departments such as coastal zone, historical review, FAA)

It’s now March 5th, 2025 and you’re getting excited.

your ADU plans are finally ready for submission. With the big technical stuff out of the way, you’re shifting into the fun zone: choosing finishes, browsing tile samples and imagining where your parents will sit for morning coffee.

Your designer now takes the full construction documents (a big digital PDF file) and prepares the official submittal.

That means uploading the plans to your local jurisdiction (in your case, the City of San Diego) through their online portal, Accela.

Pro Tip: Cities like Chula Vista, Carlsbad, or Imperial Beach have their own building departments, but most San Diego neighborhoods (like Mira Mesa) fall under the City of San Diego.

Digital Submittal Is Supposed to Be Faster… Right?

This process used to be in-person. You’d bring a roll of printed plans to the building department, drop them off at the counter, and wait for a technician to review them.

Now, it’s all online. You’d think it’s faster but in reality, it’s often slower and harder to communicate with a real person.

Still, your designer uploads the plans. Within about a week, the city processes the submission and sends back the initial invoice: the plan check fees.

You pay online. Now your project officially enters the queue.

The Waiting Game Begins

From here, San Diego’s plan review timeline is actually not bad, typically 2 to 3 weeks for the first round. While you wait, you’re working on material selections with your design team. That might mean an interior designer is helping you pick finishes, or maybe your same drafting person is wearing multiple hats and helping you finalize flooring, plumbing fixtures, and cabinetry.

By late March, the review is complete. Your designer gets an email: you’ve got comments.

Luckily, they’re minor. The design-build firm you hired is proactive, and within a week, they’ve made the revisions and resubmitted the plans.

It’s now April 5th, 2025.

The city reviews resubmittals faster—some departments have already cleared your project, so only a few remain in the loop. You’re given a new deadline: April 22nd, 2025.

The Final Stretch

On April 24th, your designer calls. The plans have officially been approved.

You receive one final invoice from the city. Once you pay, your permit is issued and your inspection card is activated.

Stamped construction drawings and approval documents are sent to your builder.

It’s May 1st, 2025. With your permit in hand, you’re ready to break ground and finally start building the home that’ll bring your family closer together. At this point, you’re roughly halfway through the full accessory dwelling unit build time in San Diego.

So, permit in hand… now what?

This is where paper turns into reality. Construction is the phase everyone thinks about first, but it only begins after months of preparation. And like everything else, the timeline can vary wildly depending on who’s running the job, how detailed the planning was, and what surprises pop up along the way.

Not sure what the actual build-out looks like, step by step? We wrote an entire article about the ADU construction process in San Diego, check it out when you’re done.

Here’s what this phase typically includes:

• Site preparation: Demo (if needed), grading, trenching for utilities, temporary fencing or porta-potty setup, and staking the ADU location.

• Foundation work: Excavation, forming, rebar installation, inspections, and concrete pour.

• Framing: Walls, roof, windows, and doors start taking shape.

• Rough-ins: Electrical, plumbing, HVAC, and low voltage work (everything inside the walls and ceilings).

• Inspections: Multiple city inspections after each major step (foundation, framing, trades).

• Insulation and drywall: Once everything behind the walls passes, insulation is installed, followed by drywall.

• Finishes: Flooring, cabinets, tile, countertops, paint, trim, fixtures, appliances, etc.

• Final inspections and punch list: This is where the city signs off on your work and you wrap up final details.

• Fast Track: 3 to 4 months (perfect weather, fully stocked materials, experienced crew, zero surprises)

• Typical: 5 to 7 months (minor hiccups, a few backorders, normal permit inspections with some corrections)

• Long: 8 to 12 months+ (weather delays, scope changes, labor or material shortages)

This is where strong project management matters. The clearer the scope, the more realistic the budget, and the faster decisions are made (especially for materials) the smoother (and shorter) construction becomes.

Let’s recap.

You started your ADU journey on January 1st, 2025, and received your signed permit on May 1st, 2025.

Now it’s time for the main course. The design-build firm has assigned you a start date: May 7th, 2025. You’ve already finalized your finishes, and pre-orders are in for the cabinets, countertops, and those beautiful red oak hardwood floors.

You cleared everything out of the garage so it can be used for storing finish materials as they arrive over the next few months.

“Mom, they gave us a start date, we’re breaking ground next week!”

Breaking Ground

The following week arrives, and the project kicks off.

A porta potty is dropped off early in the morning next to your driveway.

A 10-yard dumpster is placed at the curb for hauling dirt.

Your project manager, the site foreman, and three helpers show up to walk the site, verify measurements, and make sure everything on the plans matches real-world conditions.

“All looks good,” the foreman says, as they finish marking the site with stakes, string, and fluorescent flags.

And just like that, the digging begins.

Fast Forward to Completion

Jump ahead to February 2nd, 2026. You just received your certificate of occupancy from the city.

(You’re probably wondering what the hell happened in between. We skipped all the juicy parts.)

Here’s the thing: you can’t really template an entire construction process. It’s not that simple. Every phase comes with its own set of conditions, and every jobsite throws something new at you.

Maybe the soils report came back with bad news, and now you have to dig 12 inches deeper and increase the footing size and rebar. There goes six weeks and maybe $15,000 more than you expected.

Situations like this are one of the reasons ADU budgets can vary so much from property to property, which we explain in more detail in our guide on the cost to build an ADU in San Diego.

Or maybe framing got delayed because your lumber delivery showed up short, or you had to pull off siding after water got in during the rains. The list goes on.

The truth is, building is 50% execution and 50% solving problems you didn’t see coming.

Sometimes it’s chaos. Sometimes it’s beautiful.

But when it’s done and you’ve got that certificate in your hand, there’s nothing like it.

From the outside, building an ADU might seem straightforward, but once you’re inside the process, you quickly realize there’s a lot more to it. Permits don’t get issued overnight, construction isn’t always predictable, and every step has its own timeline.

So what should you realistically expect when building an ADU in San Diego?

• ADU Planning and design can take 6 to 8 weeks, depending on how quickly you make decisions and how complex your layout is.

• ADU permitting in San Diego usually takes 2 to 3 months, but corrections and re-submittals can add time.

• The time it takes to build an ADU in San Diego depends heavily on site conditions, utility needs, and how many surprises come up along the way. Most ADUs take 6 to 12 months to build.

• Final inspections and occupancy sign-off usually happen in the last 1 to 2 weeks, but only after everything passes city review.

Bottom line: A full ADU project in San Diego typically takes 10 to 16 months from initial planning to move-in. That includes everything: design, permitting, and construction. We hope that after reading this, you’re no longer wondering how long does it take to build an ADU in San Diego, or what the full ADU construction timeline looks like from start to finish. If you’re planning one soon, at least now you know what to expect and how to move through it with fewer surprises.