How Much Does an ADU Permit Cost in San Diego County, California?

Straight Answers on ADU Permit Costs

Built an ADU in San Diego? Or just planning? Good move. San Diego County’s rules can trip up even seasoned homeowners. This page unpacks what you’ll pay in plain language, with all the real numbers and recent law changes you need to know. No fluff, just facts. Time to see what you’re really in for.

What Is an ADU (Accessory Dwelling Unit)?

An ADU is a smaller, independent living space added to a lot with an existing home. Think backyard cottage, garage apartment, or something similar. San Diego County and most California cities are pushing for more ADUs to address housing shortages. Good news: that means some rules are relaxed and fees are sometimes lower than you’d expect.

Why Permits Are Not Optional

Every ADU in the region requires a building permit. This isn’t optional, unless you’re keen on awkward city knock-knock visits and possible fines. Permits aren’t just paperwork—they signal your project’s compliance with state and local safety codes.

A Quick Glance: Typical ADU Permit Fees in 2025

Here’s the big picture. Most ADU permit fees in San Diego County now fall between $6,500 and $21,000. Costs depend on the size, type (detached, attached, conversion), and the exact city. Units under 750 square feet benefit the most, thanks to key state law changes. Above that? Fees step up.

Common costs include:

Plan Check Fees
Building Permit/Inspection Fees
School Fees (over 500 square feet)
Water/Sewer Impact Fees
Possibly, address assignments or historic review in special cases

Permit Fee Components

The plan check fee pays city/county staff to review your submitted building plans for compliance with local and California building codes. Expect to pay $1,500 to $7,500+, with higher rates for larger ADUs or more complex plans (up to ~750 sq ft).

Plan Check Fee

Building Permit and Inspection Fee

This covers inspections during construction. On average, count on $2,000–$8,000 depending on the ADU’s size. Each city posts a schedule, and the numbers shift every July.

School Impact Fee

School districts charge projects bigger than 500 square feet. In San Diego Unified, the cost is $5.17 per sq ft—but units under 500 sq ft dodge this fee completely. For a 700 sq ft ADU, it’s about $3,619. For 1,000 sq ft, around $5,170.

Water and Sewer Fees

Water and sewer capacity fees, for connecting your ADU to utilities, aren’t small. On average:

Water: about $1,524 (reduced ADU rate)
Sewer: about $2,577 (reduced ADU rate)
New meter: If needed, can trigger a separate San Diego County Water Authority charge, starting near $5,859 for a small line.

Impact Fees

California’s SB 13 law (still in effect) waives most impact fees for ADUs under 750 square feet. Above that, the city or county may add fees for traffic, parks, and infrastructure. Some cities have further local exemptions or incentives for certain households or low-income/affordable housing ADUs.

Sample Costs Table: ADU Permit Fees by Size

ADU Size	Plan Check	Permit/Inspection	School Fee	Water/Sewer	Total (Approx.)
400 sq ft	$2,300	$2,200	$0	$4,101	$6,500
700 sq ft	$7,539	$7,834	$3,619	$4,101	$23,090
750 sq ft	$7,539	$7,834	$3,872	$4,101	$23,346
1,000 sq ft	$8,500	$8,500	$5,170	$4,101	$26,300

Estimates based on 2025 rates. Actual costs vary by municipality and project specifics.

Who Pays What—Cities Within San Diego County

Permit fees are not the same in every city. For example, Encinitas might average $3 to $5 per square foot, while San Diego City can run up to $28 per square foot for certain units. The County itself (covering unincorporated regions) has its own scales. Always check the latest city or county fee schedule.

Fee Waivers and Reductions: What’s Possible?

ADUs ≤750 sq ft: Impact fees waived by California law (SB 13).
School fees: Only hit projects larger than 500 sq ft.
Local waivers: Cities like Encinitas, Vista, and La Mesa sometimes offer extra relief for affordable housing or family/caregiver units, but conditions apply. Expect paperwork, notarized affidavits, sometimes proof of income, and ongoing occupancy restrictions.

Affordable ADU Bonus Programs

Some local programs allow property owners to build an extra ADU—or skip some fees—if they restrict that unit to affordable housing standards for a set period (usually 10 to 15 years). Sometimes that bonus comes with rent caps and must be officially recorded with the city.

Extra (Hidden) Costs to Know

Don’t stop your budgeting at city permit line items. ADU construction can carry a few less-visible fees:

Energy review (Title 24): $500–$800
Address assignment: Typically around $400–$500 if the ADU needs a formal new mailing address
Historic review: $1,000+ if your property is in a designated district
Engineering/design revisions: Can add hundreds, usually for change requests or corrections post-submittal
Added inspections: Sometimes extra fees for items like stormwater or fire safety (especially for large or complex sites)
Sewer/water upgrades: If upsizing connections, fees can spike quickly

Real-World Examples

Two scenarios, both drawn from local data and real-world case studies, underline the range:

Garage Conversion, 500 sq ft, in unincorporated San Diego:

- Plan review: $500,

- Building permit: $1,000,

- Impact fees: $2,500 (some waived under programs),

- Plumbing/electrical: $1,000.

- Total: About $5,000 (less with fee reductions).

Detached 800 sq ft ADU in a city:

Plan: $800,
Permit: $1,500,
Impact: $5,000,
Plumbing/electrical: $1,400.
Total: Around $8,700 (higher since easily crosses the key 750 sq ft line).

When and How Are Fees Paid?

Most fees are split up:

Plan Check Fees: Due up-front, with plan submittal.
Permit & Impact Fees: Paid when picking up the permit or at designated inspection milestones.
Utility/Connection Fees: Usually billed at the time of connection approval.
Special Fees: Like historic review or address assignment, these often come at specific project stages.

Payments are accepted as checks, credit/debit, and sometimes even via city/county online portals.

How Laws Have Changed the Math

SB 13: Saves thousands by waiving impact fees for smaller units.
State and local reforms: Fast-track review (60 days), removed owner-occupancy requirements, enabled multiple ADUs on one lot.
City pre-approved plans: Can cut timelines and save on resubmittals.
Utility companies: Updated procedures are now friendlier for ADU connection requests, reducing uncertainty.

ADU Permit Costs vs. Construction Costs

Remember, the permit fee is a slice—usually 10–15% of your total ADU budget. Construction, design, and site work will loom larger. But permits are a non-negotiable starting line. And, a permit makes your ADU legal (no scary letters from City Hall later).

How to Lower Your Fees and Headaches

Stay under 750 sq ft when possible

Use city/county pre-approved plans if available

Explore local fee waiver programs or affordable housing bonuses

- Keep your plans tight: revisions cost money

- Hire a designer or architect who knows San Diego ADU ins and outs

Timeline: How Long Does Getting a Permit Take?

With clean plans, expect 3–4 months from submission to approval, especially if you’re using pre-approved templates or hiring a pro. Add time if the lot is tricky, or you’re seeking waivers.

Words of Caution: Don’t Shortcut Permits

Building before permits? That’s risking fines, costly after-the-fact fixes, long delays, and resale headaches. Compliance is not optional—think of permits as a down payment on peace of mind.

Frequently Asked Questions

Q. Can I reduce my ADU permit cost?

Ans: If your unit is under 750 square feet and you meet local affordable housing guidelines, waivers are common and save big.

Q. What if my ADU is above 750 square feet?

Impact fees kick in, and school fees scale up. Aim for a smaller footprint if the permit budget is tight.

Q. Do I need permits to convert a garage or basement?

Yes. All ADU conversions require a full city/county permit and inspections.

Q. Are there programs for affordable/low-income ADUs?

Most cities in San Diego County have fee reduction or waiver programs for income-qualified units, but expect detailed income and occupancy documentation.

Conclusion: No Surprises, Only Smart Planning

Every ADU project in San Diego County comes with its own mix of required permits and fees. But knowing how these work, and what levers you can pull to cut costs, beats sticker shock every time. The current environment is the friendliest it’s been in years for affordable ADU permits—especially for compact designs and homeowners willing to do a bit of paperwork.