San Diego ADU Permit Process: Step-by-Step Timeline, Fees & Plan Check

You have the lot, the idea, and maybe even a rough budget. Then you start reading about permits and suddenly it feels like a maze of forms, fees, and waiting. How long will the city take? What will it cost before a single nail goes in? And what if your plans get sent back?

If that sounds familiar, you are in the right place. This guide walks you through the San Diego ADU permit process in plain language, from the first site check to the final inspection. You will see the realistic timeline, the fees to plan for, and how plan check actually works, so you can move forward with fewer surprises. Let’s start with what the permit process really involves.

What Is the ADU Permit Process in San Diego?

An accessory dwelling unit (ADU) is a second home on your property. It can be a backyard cottage, a garage conversion, an addition, or a junior ADU built inside your existing house. Whichever type you choose, the city treats it as a real home, which means it needs a building permit.

In San Diego, ADU permits go through the City’s Development Services Department. The good news is that California law pushes cities to approve compliant ADUs without subjective reviews. The city checks whether your plans follow the rules. It does not get to say no because a neighbor dislikes the idea.

That makes the process more predictable than most people expect. It is still detailed, though, so it helps to see the steps in order.

The San Diego ADU Permit Process, Step by Step

Most ADU projects follow the same path. Here is what happens and what to expect at each stage.

Step 1: Check Your Property and What You Can Build

Before anything else, confirm your zoning, lot size, setbacks, and any special overlays such as coastal or historic areas. This step tells you which ADU types fit your lot and how big the unit can be. Skipping it is the most common reason homeowners redesign halfway through.

Our San Diego ADU rules guide covers size limits and setbacks in more detail. Once you know what is possible, you can move on to the design.

Step 2: Choose a Design Path

You have two main options. You can have a custom design drawn for your lot, or you can start from one of the City’s pre-approved ADU plans. Pre-approved plans can cut design time and may shorten the review, but they work best on simple, flat lots. A custom design gives you more freedom with layout, finishes, and tricky sites.

XLNC Builder offers architectural design and planning alongside construction, so the same team that draws your plans also knows how to build them. That keeps the design realistic and the permit set clean.

Step 3: Prepare Your Plan Set

A complete submittal usually includes a site plan, floor plans, elevations, structural details, and energy compliance documents. Depending on your project, you may also need utility details, soil or grading information, and fire safety notes.

Complete is the key word. A missing sheet can stop the review clock, so it is worth getting everything right before you submit. Next comes the part most homeowners worry about: plan check.

Step 4: Submit Your Application and Pay Plan Check Fees

Applications are submitted through the City’s online permit system. When you submit, you pay plan check fees up front, and the city assigns your project to reviewers.

Step 5: Go Through Plan Check

This is where city staff review your drawings for zoning, structural, fire, energy, and utility requirements. We explain how this works in the next section.

Step 6: Get Approved and Pay Permit Fees

Once reviewers sign off, your project moves to a ready-to-issue status. You pay the remaining permit fees, and the city issues your building permit. Do not let this sit for long. Permits have deadlines, and waiting too long can trigger a re-review under newer codes.

Step 7: Build and Pass Inspections

Construction begins, and city inspectors visit at key stages such as foundation, framing, electrical, plumbing, and insulation. After the final inspection passes, you receive approval to occupy the unit.

Now that you can see the whole path, let’s look at the stage that tends to cause the most delays.

How ADU Plan Check Works in San Diego

Plan check is simply a review of your drawings before you build. Different reviewers look at different things, such as whether the unit meets setback and height rules, whether the structure is safe, and whether the energy and fire details are correct.

Under state law, the city has to approve or deny a complete ADU application within 60 days. That sounds long, but the clock starts only when your application is complete, and it can pause when the city sends back corrections. Many standard projects clear the first review faster than that, while complex lots take longer.

When the city sends comments, it is not a rejection. It is a list of fixes. Your designer updates the drawings, resubmits, and the review continues. A well-prepared set usually needs fewer rounds, which is why the quality of your drawings matters so much.

Here is what commonly slows plan check down:

• Missing or unclear drawings in the first submittal
• Setback or height conflicts with the lot
• Fire access or fire sprinkler questions
• Utility connection details that were not coordinated early
• Properties in coastal or historic areas that need extra review

The takeaway: most delays are avoidable with careful planning. That brings us to the timeline.

How Long Does the ADU Permit Process Take?

The honest answer is that it depends on your design, your lot, and how many correction rounds you go through. As a general guide for San Diego:

Stage	Typical Time
Site review and design	3 to 8 weeks
Plan check (first review)	A few weeks, up to the 60-day state limit
Corrections and resubmittal	2 to 6 weeks, depending on comments
Permit issuance after approval	Days, once fees are paid
Coastal Development Permit (if required)	Can add several months

From first consultation to permit in hand, most homeowners should plan for about 2 to 4 months. Construction then usually takes another 3 to 6 months, so a full project often lands in the 6 to 12 month range. For a closer look at the overall schedule, see our ADU construction guide for San Diego.

Timelines are only half the story, though. Most people also want to know what all of this costs.

ADU Permit Fees in San Diego

Permit costs are separate from construction costs, and they come in a few layers. Fees change over time and depend on the size of your unit, so treat the numbers below as planning ranges and confirm the current schedule with the city.

Plan check fees. These are paid when you submit. They vary with the size and scope of the project, and larger units cost noticeably more to review than smaller ones.

Building permit and inspection fees. These are paid when the permit is issued or as inspections happen. They cover the city’s cost of overseeing construction.

Impact fees. State law exempts ADUs under 750 square feet from most development impact fees. Larger units may owe fees, and school fees can also apply to bigger ADUs.

Utility and other fees. Water and sewer connection charges, fire review, and possible coastal permit costs can add to the total depending on your site.

Across sources, total city permit fees for a typical ADU in San Diego are commonly reported in the range of a few thousand dollars up to roughly $12,000, with bigger and more complex units landing at the higher end. Design, engineering, and surveys are separate and add to your total pre-construction budget.

Smaller units, simpler sites, and garage conversions generally cost less to permit. If you want the full picture of what you will spend, our ADU cost guide for San Diego breaks down construction and soft costs by ADU type. And if you are leaning toward a garage conversion, our garage conversion ADU guide explains the permit differences.

Once you know the fees, the next question is how to keep the process smooth.

Common Permit Mistakes That Cost Homeowners Time and Money

The city is usually not the problem. Most delays come from preventable mistakes on the homeowner’s side. Here are the ones we see most often:

• Designing before checking the lot. An ADU that ignores setbacks, easements, or utility lines will need to be redrawn.
• Submitting an incomplete set. One missing document can pause the clock.
• Ignoring coastal or historic status. These add review steps that are much easier to plan for early.
• Leaving a ready-to-issue permit unpaid. Waiting too long can lead to re-review and extra costs.
• Letting construction stall. Permits require you to start within a set time and keep inspections moving, so long gaps can put your approval at risk.
• Not budgeting for corrections. Even good plans sometimes get comments, so leave some room in both schedule and budget.

Avoiding these does not guarantee a perfect timeline, but it removes the biggest risks. Of course, you do not have to handle all of this yourself.

Should You Handle the Permit Process Yourself or Hire a Builder?

Some homeowners enjoy managing paperwork. Many do not, and the process can easily eat up evenings and weekends. Hiring a local, licensed builder who knows the city’s expectations can save you real time.

• If you want help, look for a team that can do the following:
• Check feasibility before you spend money on drawings
• Prepare complete plan sets that match city requirements
• Respond quickly to plan check comments
• Coordinate utilities, inspections, and scheduling
• Explain your costs clearly before you commit

When the same team handles design, permits, and construction, there are fewer handoffs and less finger-pointing if something needs to change. That is how we work at XLNC Builder. We are a licensed, bonded, and insured San Diego contractor (CSLB #1153455), and we handle ADU projects from the first site visit through the final walkthrough. You can see examples on our projects page.

If you are also weighing SB 9 options like a split or duplex, our comparison of SB 9 vs. ADU can help you decide which path fits your goals.

When Is It Time to Talk to a Professional?

You do not need to be fully ready to call. It is a good time to reach out if you:

• Are not sure what type of ADU fits your lot
• Live in a coastal or historic area
• Want a clear budget before committing
• Plan to finance the project and need realistic numbers
• Have already been through a plan check and received corrections

A short conversation early on can prevent months of back and forth later.

Frequently Asked Questions

Do I need a permit to build an ADU in San Diego?

Yes. Every ADU and junior ADU in San Diego needs a building permit, including garage conversions and units built inside your existing home. Building without one can lead to fines, forced removal, and problems when you sell.

Can the city deny my ADU application?

If your plans follow zoning, building, and fire requirements, the city generally cannot deny them based on discretionary reasons like neighborhood opposition. What it can do is request corrections if something in your plans does not meet the rules. Fixing those comments is a normal part of the process.

How long do ADU permits last once they are issued?

In general, you need to start construction within a limited time after the permit is issued and keep inspections moving at regular intervals. Letting the project sit idle can cause the permit to expire. Ask your builder or the city for the current deadlines that apply to your permit.

Does an ADU in a coastal area take longer to permit?

It can. Some properties in the Coastal Zone need extra review, and that can add several months. Many ADUs qualify for exemptions, so it is worth checking your address early, before you finalize your design.

Do I need extra parking for my ADU?

In most cases, no. San Diego generally does not require additional parking for ADUs, and replacement parking is typically not required when you convert a garage. Special situations can exist, so confirm with your builder based on your lot.