1. Get Clear on What You’re Building
Before you even think about applying, you need to know what kind of ADU you're planning. Detached? Garage conversion? Junior ADU?
Each type follows slightly different rules. For example:
Detached ADUs can be up to 1,200 sq. ft.
Attached ADUs are limited by the size of your existing home.
Junior ADUs (JADUs) cap out at 500 sq. ft. and must be part of the existing house.
Why does this matter? Because how you define your ADU determines your path through the permit process.
2. Research Zoning and Site Conditions
Next, you’ll want to dig into your property’s zoning. San Diego’s municipal code is friendly to ADUs, but there are still limits. Zoning affects:
Setbacks (how close you can build to property lines)
Height restrictions
Parking requirements (though many have been waived)
Use the City’s ADU regulations site to search your address and confirm eligibility. Have a sloped lot? Easement running through the backyard? These can throw wrenches in the plan. Better to know now.
3. Develop a Basic Concept
At this stage, you don’t need final blueprints—but you do need a concept.
Where will the unit go?
How big will it be?
Will utilities connect to the main house?
This is also when you start thinking about design. Not for aesthetics, but for code. For instance, San Diego requires fire separation between units. You’ll also need to consider access, especially for detached ADUs in tight spaces.
4. Hire a Professional
You can DIY a lot of things. Permitting isn’t one of them.
Even if you have construction experience, the city wants clean drawings, legal documents, and clear maps. A licensed professional—typically an architect or a designer familiar with San Diego ADUs—can prep everything the city wants to see.
You’ll need:
- Site plan
- Floor plan
- Elevations
- Utility plan
Without these, your ADU permit application won’t get far.
5. Submit Your Plans Online
San Diego uses a digital permitting system called OpenDSD. This is where you upload your drawings and documents. You’ll also need to fill out the Project Application Form and, in some cases, a Stormwater Form.
The city charges plan check fees here—usually between $1,000 and $3,000 depending on your unit size. Expect a confirmation email. Then the waiting begins.
6. City Review Process
This is where patience pays off. The city will review your plans across several departments:
Planning (zoning, setbacks)
Engineering (drainage, grading)
Building (structural, fire code)
Transportation (driveways, parking)
Utilities (water, sewer, power)
If something’s missing or off, you’ll get a correction notice. This means you’ll need to revise the plans and resubmit. Most projects get approved in 2 to 6 months, depending on how complete your submittal was and how complex the build is.
7. Permit Issuance
Once your plans pass review, you’ll be issued a permit. This is your green light to start building.
At this stage, you’ll also need to pay additional permit fees, which can run from $5,000 to $15,000 depending on your ADU size and site conditions. These are separate from plan check fees. Be sure to post your permit on-site before construction begins.
8. Construction and Inspections
Time to build. But don’t think you’re home free yet. The city will inspect your site at key stages:
Foundation
Framing
Electrical and plumbing rough-ins
Insulation
Final inspection
You’ll schedule each one through the city’s portal. Fail an inspection? Fix it and call them back. It’s normal. Don’t sweat it. This phase usually takes 3 to 6 months. Weather, labor availability, and material delays can all shift that timeline.
9. Final Approval and Certificate of Occupancy
Once you pass your final inspection, the city issues a Certificate of Occupancy (CO). This document legally allows someone to live in the ADU.
No CO = no tenant.
You’ll want to save a copy in your records, especially if you plan to refinance or sell down the line.
10. Bonus: Avoiding Common Pitfalls
Some common mistakes that slow people down:
Submitting incomplete plans
Not checking for utility easements
Skipping soil or topography checks on tricky lots
Not responding to city comments fast enough
Starting construction before permit approval (just don’t)
Also, don’t rely on rumors from forums or neighbors. ADU rules shift regularly in California. Always check the latest guidelines or consult a pro.
11. How Long Does It Take, Really?
Let’s be real. Even with all your ducks in a row, this isn’t overnight. From concept to CO, expect 8 to 12 months for a standard ADU project in San Diego. Faster if it’s a garage conversion. Longer if you’re dealing with a hillside or utility upgrades.
The key is preparation. A well-prepared project sails through. A sloppy one stalls.
12. Wrapping It Up
Building an ADU in San Diego is doable—but it’s a process. One that starts with knowing your property and ends with a legal, livable unit in your backyard. It’s not just about construction. It’s about understanding city rules, working with professionals, and moving through each step methodically.
If you’re serious about building, take the time to prep right. It’ll save you time, money, and a whole lot of stress. And if the paperwork already feels overwhelming? No shame in getting help. Most of our clients would rather deal with drywall than documents.
