ADU vs. JADU: Which One Fits Your Lot, Your Budget, and Your Goal
The confusion between these two is real and it costs homeowners money. Get the category wrong and you either pay $80,000 more than you needed to, or you build something that ties you to the property long after you wanted to move on.
An ADU (accessory dwelling unit) is an independent dwelling: its own kitchen, its own bathroom, its own entrance. It can be a new detached structure in your backyard, a garage conversion, or a new addition attached to your house. A JADU (junior accessory dwelling unit) is something smaller and more constrained: a unit carved out of the existing footprint of your home, capped at 500 square feet under California state law, with an efficiency kitchen instead of a full one, and an option to share plumbing with the main house if needed. Think a converted bedroom suite with a kitchenette and a private entry door.
Both produce a second housing unit on a single-family lot. The path to get there, and what you’re allowed to do with it afterward, are very different.
What the law actually says
In California, the JADU framework was originally codified in Government Code §65852.22. SB 477, signed March 26, 2024, relocated those provisions to Government Code §66333 through §66339 as part of a technical consolidation. The substance did not change. Only the location in the code changed.
The core requirements under §66333 (formerly §65852.22):
- The JADU must be created within the space of an existing single-family home or its attached garage. No new detached structures qualify as JADUs.
- Maximum size: 500 square feet. This is a hard ceiling in state law. Your city cannot raise it.
- Kitchen: an “efficiency kitchen” is permitted, meaning a small cooking area without a full range. A two-burner induction cooktop, a compact refrigerator, and a sink. Not a full kitchen with a range and exhaust hood.
- Bathroom: the JADU may share a bathroom with the main house. If it does, the owner-occupancy requirement kicks in.
- One JADU per single-family lot, regardless of lot size.
- A deed restriction must be recorded at permitting, binding future owners to the same restrictions.
An ADU has no equivalent size ceiling under California state law (though cities can set their own limits, often 800-1,200 square feet), and no efficiency-kitchen limitation. It must be fully self-contained.
The side-by-side
[IMAGE NEEDED: Two-column comparison diagram showing JADU (within existing home footprint, 500 sq ft cap, efficiency kitchen, shared utilities possible) vs. ADU (independent structure, own utilities, full kitchen, no state size cap)]
| JADU | ADU | |
|---|---|---|
| Max size | 500 sq ft (state hard cap, §66333) | No state maximum; city limits typically 800-1,200 sq ft |
| Kitchen | Efficiency kitchen only (no full range) | Full kitchen required |
| Bathroom | May share with main house | Must be self-contained |
| Owner-occupancy | Required (§66333) when bathroom is shared; owner must live in main house or JADU | Not required in California for standard ADUs |
| Sell separately | No (cannot be separately deeded) | Possible in cities that have opted into AB-1033 (2023): San Jose, San Diego, Berkeley, Santa Monica, and others; list expanding |
| Typical all-in cost | $40,000-$120,000 | $80,000-$300,000+ depending on type |
| Permitting timeline | 4-8 weeks (ministerial review, state law) | 8-20 weeks (more systems to review) |
| Rental rules | Can rent long-term; local STR ordinances still apply | Same (local STR rules still apply) |
| Property tax | Reassessment only on the value added by the conversion | Same (added value assessed at completion) |
The table makes one thing clear: JADUs win on cost and speed. They lose on size, kitchen configuration, owner-occupancy rules, and future flexibility.
The owner-occupancy rule
This is where people get surprised.
Under Government Code §66333, if your JADU shares a bathroom with the main house, the owner is required to occupy either the primary residence or the JADU itself. That covenant is recorded as a deed restriction at permitting. It runs with the property. If you sell the house, the new owner inherits it. If you rent out the main house and move across town, you are in violation.
California does not impose an owner-occupancy requirement on standard ADUs. That exemption does not extend to JADUs with shared sanitation. The JADU owner-occupancy rule remains in force under §66333.
The practical implication: if there is any realistic chance you will move out in the next five to ten years, the JADU locks you into a situation you have not fully decided. An ADU does not.
One workaround worth knowing: if your JADU has its own private bathroom (not shared with the main house), the city may not be required to impose the owner-occupancy restriction. Check your city’s JADU ordinance before defaulting to the shared-bath configuration to save money. The owner-occupancy constraint can cost more in lost flexibility over time than a separate bath adds in construction cost.
When a JADU makes sense
JADUs fit a specific set of circumstances well.
You have the right existing space. The strongest JADU candidates are attached garages that feel too small for a full ADU conversion, large bedroom suites with exterior doors, or first-floor bedroom clusters that can be isolated with a private entry. If the space already reads as “almost separate,” a JADU can complete the conversion for $50,000-$80,000 in most California markets. (Source: verifiedadu.com JADU California guide, 2026; aduguru.us JADU cost breakdown, 2026.)
You are staying put. If you plan to live on the property long-term and won’t need to rent both units simultaneously, the owner-occupancy restriction describes what you were going to do anyway. It is not a real constraint until your plans change.
Budget is the binding constraint. A straightforward JADU conversion (private entry, efficiency kitchen, permit, minor plumbing) can come in under $80,000 in most California metros outside the Bay Area. That is roughly half the cost of a basic garage conversion ADU and less than a third of a detached new build. If the budget is tight and the space works, the JADU math often wins. See the full California ADU cost breakdown for what the detached alternative actually runs by region.
Single occupant. An efficiency kitchen with 500 square feet is a real living space for one person: an aging parent, a grown child, a long-term single tenant. It is a tight fit for two people with any possessions and almost no life.
When a standard ADU is the right answer
The ADU becomes the clear choice when any of the following is true.
You need more than 500 square feet. A 1-bedroom unit for two people, a guest house with a real kitchen, a rental that will compete at standard market rates: all of these want more space. JADUs cannot get there. Full stop.
You want a full kitchen. An efficiency kitchen works for reheating and simple meals. Someone who cooks, who has a family, or who will live there for years needs a real range. The kitchen limitation is not cosmetic. It is a daily quality-of-life issue that shows up every single night.
You might move out. Any chance of renting the main house, selling and moving elsewhere, or eventually wanting to rent both units as market-rate rentals means the JADU owner-occupancy restriction is a liability rather than a non-issue. It will follow the property to a future buyer and show up in your negotiation. An ADU carries no such burden.
You want the option to sell separately. AB-1033 (2023) allows standard ADUs to be separately titled as condominiums in cities that have passed a local enabling ordinance. As of mid-2026, four jurisdictions have confirmed adoption: San Jose (ordinance effective July 18, 2024; first closings August 2025), the City of San Diego (council approved the opt-in package June 18, 2025, effective August 22, 2025), Berkeley (council voted 6-1 in January 2026), and Santa Monica (early 2025). (Sources: KQED, “San Jose Developers Pioneer New California Law, Selling ADUs as Condos,” kqed.org; ADU Geeks, “AB 1033 Opens the Door to Selling ADUs in San Diego,” adugeeks.com; Berkeleyside, “Berkeley Legalizes Sale of ADUs,” January 21, 2026, berkeleyside.org.) Los Angeles and Sacramento have studied the option but have not yet enacted enabling ordinances as of this writing. The list is expanding; check your city’s planning department for current status before counting on this option. A JADU does not qualify for separate sale under AB-1033 regardless of where the property is located.
Rental income is a primary goal. A 750-square-foot ADU in a mid-market Los Angeles neighborhood — South LA, the eastern San Fernando Valley, outer East LA — with a full kitchen rents for roughly $1,800-$2,400 per month. (Citywide, detached ADU rents across the LA metro run $2,200-$2,800; mid-market suburban neighborhoods track toward the lower half of that range. Source: Zumper and RentCafe spring 2026 median rent data as compiled in the California ADU rental income guide, which covers seven California metros.) A comparable JADU at 500 square feet with an efficiency kitchen in the same neighborhoods runs $1,200-$1,600. (No large-sample JADU-specific rent index exists; the figure reflects a size-and-kitchen-quality discount from the ADU baseline — roughly 65-70% of ADU rent for the same area, consistent with the smaller footprint, no full range, and the occasional shared-bath configuration that limits renter demand.) The rent differential over five years can offset a large portion of the cost gap between the two unit types. The garage conversion comparison has the cost-per-square-foot math if you are considering that path as an intermediate option.
A note on geography
JADUs are a California-specific legal category. The name, the 500-square-foot cap, the efficiency-kitchen standard, and the owner-occupancy framework all come from California Government Code §66333 (formerly §65852.22). Other states do not have this category by name.
Oregon’s HB-2001 (2019) and Washington’s HB-1337 (2023) both streamlined ADU permitting statewide and made interior conversions of single-family homes easier to permit. But those states call them ADUs, or attached ADUs, or interior ADUs. Not JADUs. The economic logic is similar (use existing structure, save on foundation and framing), but the specific rules, size caps, and ownership restrictions differ.
Outside the West Coast, ADU and interior conversion legislation is patchwork. Some states have passed real reform; many have not. If you are outside California, look for your state’s “attached ADU” or “interior ADU conversion” permit pathway. Do not assume the JADU framework or any of its specific rules apply to you.
The cost gap in plain numbers
A JADU conversion within an existing single-family home: $40,000-$120,000 all-in, depending on the condition of the existing space, the extent of plumbing work, and finish level. Simple bedroom-to-JADU conversions with an existing adjacent bath can come in below $60,000. Conversions requiring a new efficiency kitchen, new plumbing rough-in, and a separate bath move toward the $100,000-$120,000 range. (Source: verifiedadu.com, 2026; aduguru.us, 2026.)
For comparison:
- Garage conversion to ADU: $80,000-$150,000 (1-car) or $120,000-$220,000 (2-car). The garage conversion cost breakdown has the full line-item table.
- Detached new build: starts around $165,000 in lower-cost California markets and runs to $360,000 in the Bay Area for a 600-square-foot unit. The national ADU cost guide explains what drives that range and how to read a contractor bid.
The JADU is cheaper, but the savings come with real constraints. This is not “same outcome for less money.” It is a different outcome for less money: smaller, simpler, with more restrictions on what you can do with it afterward.
Where to start
If you’re in California: pull your city’s JADU ordinance. State law sets the floor, but cities can add requirements on top of it. Some require a separate bathroom. Some have additional kitchen standards beyond the state minimum. Know what your city requires before you budget.
Measure the space you are thinking about converting. Is it actually 500 square feet or less? Is there a private exterior entry, or would you need to build one? Is there an existing bath that could be shared, or would you need to add one? Those three questions will tell you whether a JADU is even on the table.
If it is, get two bids: one from a contractor who has done JADUs and one from a contractor who focuses on standard ADU conversions. Ask each to scope the project specifically against §66333 requirements. The bids will differ. The difference tells you something about which path fits your situation.
If you’re outside California: search your state housing agency for ADU conversion guidelines. The economics of using existing structure versus building new apply everywhere. The JADU name and California’s specific rules do not.