ADUs in San Diego: Rules, Costs and Rental Income Potential

by Trevor Landress

An ADU, or accessory dwelling unit, is a second home on the same lot as a main home, and in the City of San Diego it can be 150 to 1,200 square feet. At the time this article was written (October 2026), the City's Information Bulletin 400 said an ADU can be attached or detached and must have complete living facilities. Building one costs real money. A 2021 UC Berkeley survey, cited in a California Assembly committee analysis, reported median construction costs of $100,000 to $177,500.

The short answer

City of San Diego ADUs can be attached or detached, from 150 to 1,200 square feet.
The owner is not required to live on the property, and the unit cannot be rented for fewer than 31 days at a time.
A 2021 survey reported median build costs of $100,000 to $177,500. Your cost depends on the design and the site.
Rent is not guaranteed. My example below is made up and ignores many costs.
I am a REALTOR, not a contractor, lender or attorney. Confirm rules with the City.

What counts as an ADU in the City of San Diego

The City defines an ADU as an attached or detached home that is 1,200 square feet or less. It must have complete, independent living facilities, with permanent places for living, sleeping, eating, cooking and sanitation. It sits on a lot that has, or will have, a main home.

ADUs are generally allowed in zones that permit homes. The City says the owner does not have to live on the property. It also says an ADU may not be rented for fewer than 31 consecutive days. That means no short-term stays.

A smaller unit that sits inside the main home is a different thing, called a junior ADU. I compare the two in my guide to junior ADUs vs. detached ADUs.

Size, height and setbacks

At the time this article was written, Information Bulletin 400 listed these main rules for ADUs. Details change by zone and lot.

Topic	What the City bulletin says
Size	150 to 1,200 square feet. ADU floor area counts toward the lot's floor area ratio, with an exception for one ADU up to 800 square feet.
Height	On lots zoned for one home, a detached ADU can be no more than two stories. It must also follow the zone's height limit.
Front yard	Must meet the zone's front setback.
Side and rear yards	A new ADU may go up to the property line unless building code rules apply. If it is taller than 16 feet and next to a residential lot, it needs a 4 foot setback, or the zone's setback if that is smaller.
Very High Fire Hazard Severity Zone	A 4 foot setback applies at the side and rear, no matter the height.
Converted buildings	An existing building that becomes an ADU can keep its current setbacks.

The bulletin also says some rules are not yet in force in the Coastal Overlay Zone. They start when the California Coastal Commission certifies them. If your lot is near the coast, ask the City what applies.

Fees and other requirements

The City's bulletin names several costs and rules. It does not give one total price, because fees vary by project.

A General Plan Maintenance Fee applies to all ADUs and junior ADUs, starting August 9, 2022.
ADUs are subject to Development Impact Fees under the municipal code.
Projects with more than one ADU pay Regional Transportation Congestion Improvement Program fees.
ADUs are not exempt from the City's inclusionary housing rules.
An ADU needs fire sprinklers if the main home has them. It does not need them if the main home does not.
ADUs must follow the City's rules for trash, recycling and organic waste storage.

The City also has a bonus program. In Sustainable Development Areas, one extra non-deed-restricted bonus ADU is allowed for each qualifying deed-restricted ADU. Outside those areas, the maximum is one bonus ADU. Ask the City whether your lot qualifies.

What an ADU can cost to build

A California Assembly committee analysis from April 2025 summed up a 2021 survey of owners of permitted ADUs. The survey, by the UC Berkeley Center for Community Innovation, found median construction costs ranging from $100,000 to $177,500. The analysis says detached ADUs cost more to build than garage conversions.

This survey is five years old, so costs today may differ. The analysis was also a bill review, not a bid. Get written quotes from licensed contractors for your own lot. The same analysis says a survey of coastal-market owners found that over a third rented their ADUs at rates considered affordable for lower-income households.

A made-up look at rental income (my math)

I do not have a sourced rent figure for San Diego ADUs, so this table uses made-up rents. It divides the 2021 cost range by yearly rent. It shows years until rent adds up to the build cost. It ignores taxes, loan interest, insurance, utilities, repairs, empty months and the time it takes to find a tenant. In real life, payback takes longer.

Made-up monthly rent	Yearly rent	Years to match $100,000	Years to match $177,500
$2,000	$24,000	4.2 years	7.4 years
$2,500	$30,000	3.3 years	5.9 years
$3,000	$36,000	2.8 years	4.9 years

New construction is also reassessed for property tax. My guide to how San Diego property taxes work explains that rule. A lender or CPA can help you work out the full cost of an ADU for your lot.

Steps to take before you plan an ADU

The City's bulletin is guidance for getting a building permit to build an ADU. So a permit is part of the path, and the order of your steps matters.

Find your zone, and check whether your lot is in the Coastal Overlay Zone or a Very High Fire Hazard Severity Zone. Each can change the rules.
Compare your lot to the height and setback rules in the table above.
Ask the City about fees and about the bonus program.
Get written quotes and ask what the price includes.
Talk to a lender or CPA about how to pay for it and how it may affect your taxes.

Selling a property with an ADU

The City's bulletin says new or existing ADUs may be made into condominiums and sold apart from the main home, if they meet the municipal code. That takes a subdivision process, so it is not a quick change. If you plan to sell, my guide on the cost to sell a home in San Diego shows the normal sale costs.

Buyers should ask for permit and final inspection records on any ADU. Those records help show the City approved the unit.

This is not a guarantee

City rules change often. The bulletin I read lists amendments from 2023, 2024 and 2025, and it says some parts are on hold in the Coastal Overlay Zone. Your zone, lot shape, utilities and fire zone all matter.

Costs and rents are also not guaranteed. A 2021 cost range is not a quote, and my rent table is only a math exercise.

My advice for San Diego homeowners and buyers

Call the City of San Diego Development Services Department with your address before you hire anyone.
Get at least two written quotes from licensed contractors, and ask what is not included.
Plan for fees, sprinklers, utility work and property tax, not just construction.
If you want rent, plan for the 31 day minimum and budget for empty months.
If you are buying a home with an ADU, ask for permit records and the final inspection.

Call or text me at (619) 402-4614 or send me a message.

Call or text (619) 402-4614 Contact Trevor Landress

Related guides

Frequently asked questions

How big can an ADU be in San Diego?

At the time this article was written, the City of San Diego said an ADU can be 150 to 1,200 square feet. There is an exception that lets one ADU up to 800 square feet exceed the lot's floor area ratio.

Do I have to live on the property if I build an ADU?

At the time this article was written, the City of San Diego said the property owner is not required to live on site. Check the City if your rules may be different.

Can I rent my ADU as a short-term rental?

At the time this article was written, the City said an ADU may not be rented for fewer than 31 consecutive days, so short stays are not allowed.

How much does it cost to build an ADU in San Diego?

A 2021 survey cited by a California Assembly committee reported median construction costs of $100,000 to $177,500. That is not a quote, and your cost depends on your lot, design and contractor.

Can an ADU be sold separately in San Diego?

The City says new or existing ADUs may be made into condominiums and sold apart from the main home if they meet the municipal code. It requires a subdivision process.

About the author

Trevor Landress is a San Diego REALTOR® with Coldwell Banker West (DRE# 02126901). He was born and raised in San Diego and has been licensed since 2021. Trevor helps homeowners sell, guides first-time buyers through the home buying process and assists investors with their next acquisition. His work includes negotiating offers, analyzing market trends, building pricing strategies and running marketing campaigns for his listings.

He serves clients across San Diego County, from coastal communities like La Jolla, Del Mar and Carlsbad to neighborhoods inland. Trevor is part of the Campbell Group, a three-generation real estate team, and he and the Campbell Group consistently rank as a top producing team at Coldwell Banker West each month. He writes these guides to help San Diego buyers and sellers navigate an ever-changing market.

Each guide on this blog is built from official or primary sources, and the text names the source and the month it was checked. When a fact can go stale, such as a rate, a fee, a deadline or a rule, the guide says so. The goal is plain answers you can use before you make a big decision.

Trevor is a REALTOR, not a tax advisor, attorney, lender or contractor. For questions in those areas, he recommends you check with the right professional. To talk through your plans, call or text (619) 402-4614 or contact Trevor Landress.

How I help San Diego home buyers

Trevor guides first-time buyers through the home buying process, from setting a budget to closing. His work includes negotiating offers and analyzing market trends so buyers understand what a home may really cost to own.

How I help San Diego home sellers

Trevor helps homeowners sell with pricing strategies, marketing campaigns, offer negotiation and market analysis, so sellers know what to expect before they list.

Sources

This guide is general information, not tax, legal, construction or financial advice. I am a REALTOR, not a tax advisor, attorney, contractor or lender. Please confirm your situation with a CPA, an attorney or the right agency before you act.