Junior ADU vs. Detached ADU in San Diego: Which Fits Your Home?

by Trevor Landress

A junior ADU, or JADU, is a small unit of no more than 500 square feet that is built inside your existing single-family home, while a detached ADU is a separate building in your yard. At the time this article was written (October 2026), the City of San Diego's companion and junior units page said a JADU must sit entirely inside the home and may share a bathroom with it. A detached ADU needs its own complete living space, including a bathroom.

The short answer

A JADU lives inside your home and is small. A detached ADU is its own building.
A JADU can share a bathroom with the main home. A detached ADU needs full living facilities.
A JADU cannot be sold apart from the home. An ADU may be made into a condo in the City of San Diego.
The City lists JADUs as outside its bonus program, and state guidance says JADUs need owner occupancy.
I am a REALTOR, not an architect, contractor or attorney. Confirm rules with the City.

The basic difference

The City of San Diego describes an ADU as an attached or detached home on a lot with a main home, with permanent places for living, sleeping, eating, cooking and sanitation. A JADU is different. The City says it must be entirely inside a single-family residence, and it needs a kitchen or an efficiency kitchen. It may share sanitation, which means a bathroom, with the main home.

The state housing agency, HCD, describes JADUs as typically a bedroom in a single-family home. It has an entrance to the outside and an entrance to the main home. Cooking facilities must include a sink. For the full rules on full-size units, see my guide to ADUs in San Diego.

Side by side

At the time this article was written, the City's page and the state FAQ gave these differences.

Topic	Junior ADU (JADU)	Detached or attached ADU
Where it goes	Inside a single-family home, only in single residential zones	On a lot with a main home, in single, multiple and mixed-use zones and some planned districts
Size (City)	150 to 500 square feet	150 to 1,200 square feet
How many (City)	One	Up to 2 in single-dwelling zones, 2 or more in multiple-dwelling zones
Bathroom	May share with the main home	Complete living facilities
Entrance (state FAQ)	Separate entrance to the outside, plus one to the main home	Depends on the design
Parking (City)	None required	Generally none, except near the beach
Agreement (City)	JADU Agreement required	None required
Owner occupancy (state FAQ)	Required	Depends on local rules
Sold apart from the home	No, per the state FAQ	Possible as a condo in San Diego, per the City
City bonus program	Not part of it	Eligible under its rules

The state FAQ is undated, and California lawmakers have looked at changes to JADU rules since it was written. I could not confirm the final result, so ask the City which rules apply today.

When a junior ADU may fit

A JADU turns space you already have into a small home. The state FAQ says JADUs share the home's central systems, need no fire separation and have a basic kitchen with small plug-in appliances. That can lower the cost. It also says the doors between the two spaces can be locked from both sides, so you can open the space back up later.

The state FAQ also says JADUs should not be charged water, sewer or power connection fees, since they are not considered a new unit for fee purposes. Local rules may still add other charges, so ask the City.

The tradeoff is privacy and size. A JADU shares walls and often a bathroom with the main home. Because the owner must live on the property under state guidance, it may suit a family member, a caregiver or a roommate.

When a detached ADU may fit

A detached ADU gives more space and more separation. It can be as large as 1,200 square feet under City rules, with its own entry and full facilities. It costs more to build, since it needs its own systems. Cost data and size rules are in my ADU guide.

The City also allows an ADU to be sold apart from the main home as a condo. A JADU cannot be sold apart, per the state FAQ. The City says the condo path takes a subdivision process under its municipal code. It adds that for 30 days after the first listing, the unit must be offered to buyers who will live there as their main home. ADUs built through the bonus program cannot be sold apart.

Questions to ask the City before you choose

Can my lot have a JADU and an ADU together, or only one?
Which owner occupancy rule applies to a JADU on my lot today?
What does the JADU Agreement say, and does it have to be recorded?
Is my lot in the Coastal Overlay Zone, which has its own page and rules?
Do fire sprinklers or solar apply to my plan?

Write the answers down and keep the staff member's name and the date. Rules can change, and a written record helps if the City's guidance changes later.

Rules that apply to both

A building permit is required, and the City says there are no exemptions.
Neither type can be rented for fewer than 31 consecutive days.
Fire sprinklers: a detached ADU is exempt only if the main home has none and the unit meets certain occupancy rules. Attached ADUs and JADUs need sprinklers if the main home has them.
Newly built detached ADUs must provide solar under the state energy code. JADUs do not.
A garage conversion in the Beach Impact area may require a replacement parking space, with exceptions.

The City also lets applicants use preapproved plans from the County of San Diego, Chula Vista or Encinitas. Under state law AB 1332, a project using those plans gets a 30 day review, but it must still meet San Diego's code. You license the plan from its provider.

This is not a guarantee

The City page I used does not cover school fees, and it says other fees vary by project. The state FAQ is not dated. Rules may be different in the Coastal Overlay Zone, which has its own City page.

Your lot, your zone and your plan decide what is possible. Ask the City before you spend money on designs. New construction can also be reassessed for property tax, so read my guide to how San Diego property taxes are calculated.

My advice for San Diego homeowners and buyers

Start with your goal: a family member, a renter or extra space. Then match it to a JADU or an ADU.
Ask the City which version of the JADU owner occupancy and parking rules applies right now.
If you want to sell the unit later, ask the City about the condo path before you build.
Check the fire sprinkler rule for your main home early, since it can change your cost.
Ask about preapproved plans, and get quotes from licensed contractors.

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

What is the difference between a JADU and an ADU?

A junior ADU is no more than 500 square feet and sits inside your single-family home, and it can share a bathroom. A detached ADU is a separate building with full living facilities.

How big can a junior ADU be in San Diego?

At the time this article was written, the City of San Diego said a JADU can be 150 to 500 square feet. The City allows one JADU per lot, in single residential zones.

Does a JADU require the owner to live on the property?

The state housing agency's FAQ says owner occupancy is required for a JADU. Lawmakers have looked at changes since then, so ask the City which rule applies today.

Can I sell a JADU or ADU separately?

The state FAQ says a JADU cannot be sold apart from the main home. The City says an ADU may be made into a condo and sold separately, with a subdivision process and a 30 day owner-occupant offer period.

Do I need sprinklers in a JADU or ADU in San Diego?

At the time this article was written, the City said attached ADUs and JADUs need sprinklers if the main home has them. A detached ADU is exempt only if the main home has none and the unit meets occupancy rules.

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.