Garage conversion impact fees in San Diego: what state law actually waives

Do you owe impact fees on a garage conversion in San Diego?

If your garage-to-ADU conversion keeps interior livable space at 750 square feet or less, state law says no local agency can charge you an impact fee for it. That’s not a San Diego giveaway. It’s California Government Code §66311.5, and it applies the same way in the City of San Diego, Chula Vista, Escondido, or any of the county’s other jurisdictions. Above 750 square feet, the fee comes back, but only in proportion to your unit’s size against the main house. The catch homeowners keep missing: “impact fee” is a specific legal term. It doesn’t cover plan check, permit issuance, or school fees, so a garage conversion impact fees san diego search that ends at “it’s free” leaves you short at the counter.

What the impact-fee exemption actually says

The statute is direct: a local agency, special district, or water corporation “shall not impose any impact fee upon the development of an accessory dwelling unit that has 750 square feet of interior livable space or less.” For a junior ADU, the threshold is 500 square feet. Most single-car and two-car garage conversions in San Diego land well inside that window, so the exemption covers a real share of garage conversions in the county.

Go over 750 square feet and the exemption stops applying cleanly. Fees “shall be charged proportionately in relation to the square footage of the primary dwelling unit,” which means a larger ADU pays a fraction of what a full new home would owe, scaled to size, not the full impact-fee schedule.

There’s a second piece worth knowing if you’re converting a garage into an ADU rather than building one from scratch: state law also blocks cities from treating that conversion as a new residential use for water and sewer connection fees, as long as no new or separate utility connection is required. A garage that already shares plumbing and electrical infrastructure with the main house generally doesn’t trigger a fresh connection charge under this rule.

What “impact fee” doesn’t cover

This is where garage conversion impact fees san diego confusion causes real budget problems. Impact fees are development fees tied to the burden a new unit places on infrastructure like parks, roads, and public facilities. They are not the same as:

Plan check fees, charged for the city or county reviewing your submitted drawings against building, electrical, plumbing, and energy code.

Building permit fees, charged for issuing the permit itself and inspecting the work as it happens.

School impact fees, which are set by your school district, not your city, and apply separately once your ADU exceeds 500 square feet of new habitable space.

None of those disappear under the 750-square-foot exemption. This site does not publish City plan-check, permit, or school-fee totals. Confirm every line with the department and the school district that serve the property. A homeowner who reads “no impact fees under 750 square feet” and assumes the permit process is free is planning around a number that was never accurate.

Why the 60-day clock matters for your budget too

Impact fees aren’t the only piece of state law working in a garage conversion’s favor. California Government Code §66317 requires a local agency to approve or deny a completed ADU application within 60 days. If the agency misses that window, the application is deemed approved by law.

That clock only starts once your application is complete, not the day you first submit it, and it can be tolled if you’re the one causing a delay. It’s also a decision deadline, not a construction guarantee. Still, it matters for your budget in a way people don’t connect to fees: every extra month a project sits in plan check is a month you’re paying rent, a mortgage, or storage costs without a finished unit, and jurisdictions that drag past the statutory window are the exception, not the rule, once your application is genuinely complete.

San Diego’s jurisdiction split still applies

The impact-fee exemption is state law, so it doesn’t change based on where in the county you live. What does change is who processes your application and what non-impact fees they charge. Properties inside an incorporated city (San Diego, Chula Vista, Escondido, and the county’s other cities) go through that city’s building department. Properties in unincorporated areas go through the San Diego County Department of Planning and Land Use. Both are bound by the same §66311.5 exemption and the same §66317 clock; they just run different plan check queues and fee schedules for the pieces the exemption doesn’t touch.

The mistake to avoid

Don’t walk into a permit counter, or a contractor conversation, saying “my ADU is under 750 square feet so I owe nothing.” Say instead: “I understand impact fees are exempt under Government Code §66311.5 for units under 750 square feet, what plan check and permit fees will apply to my project.” That question gets you an accurate number instead of a surprise at issuance. It also flags a contractor who doesn’t know the current exemption, which is a red flag on its own since the law renumbered from the old §65852.2(f) citation and some fee schedules and quotes online still haven’t caught up.

If you’re weighing a garage conversion against building a detached ADU from scratch, the impact-fee math is one more reason garages come out ahead: you’re starting from an existing foundation and structure, which keeps you inside that 750-square-foot exemption more often than a from-scratch build with more room to add square footage.

For a full breakdown of what a San Diego garage conversion costs beyond fees, see our garage conversion cost guide. For the statutory 60-day approval window in more depth, see ADU permit timeline. For the exemption itself and how it’s calculated above 750 square feet, see ADU fees and impact fees.

To connect with insured local crews who know the current fee schedule and impact-fee exemption in your jurisdiction, visit the garage conversion service page or call (858) 400-4935. Homeowners in La Mesa and National City ask about this exemption often, since both cities process ADU conversions at city hall rather than through the county. For help navigating the plan check and permit paperwork itself, see our permits and plans service. Always verify any contractor’s license at cslb.ca.gov before signing anything.

Are impact fees really waived for garage conversions in San Diego?

Yes, for the impact fee specifically, if your converted ADU keeps 750 square feet or less of interior livable space (500 for a junior ADU). This is California Government Code §66311.5, not a local San Diego program, and it doesn’t waive plan check, permit, or school fees.

What happens if my garage conversion goes over 750 square feet?

The impact-fee exemption no longer applies in full. Instead, fees are charged proportionately based on your ADU’s square footage relative to the main house, rather than the full fee a new single-family home would owe.

Do I still pay school impact fees on a garage conversion under 750 square feet?

Yes. School impact fees are a separate fee category set by your school district, not covered by the §66311.5 impact-fee exemption, and typically apply once your ADU adds habitable square footage over 500 square feet.

Does the 750-square-foot exemption apply everywhere in San Diego County?

Yes. It’s state law, so it applies the same way in every incorporated city and in unincorporated areas processed through the county. What varies by jurisdiction is the plan check and permit fee schedule, not the impact-fee exemption itself.

How long does the city have to approve my garage conversion permit?

State law gives the local agency 60 days from a completed application to approve or deny an ADU permit. If they miss that window, the application is deemed approved. The clock starts at a complete application, not your first submittal.

Can a contractor tell me my exact impact fee before submitting plans?

A contractor can tell you whether the 750-square-foot exemption likely applies to your project, but the exact plan check and permit fee total comes from your jurisdiction’s current fee schedule, pulled at submittal. Be cautious of anyone quoting a flat number before that.