A junior accessory dwelling unit (JADU) is a small home of up to 500 square feet built inside your existing single-family house, often in a spare bedroom or an attached garage. It needs its own exterior entrance and an efficiency kitchen, and it can have its own bathroom or share one with the main house. Since AB 1154 took effect on January 1, 2026, a JADU with its own bathroom has no owner-occupancy requirement, so you can rent out both the JADU and the house. Most JADUs cost $50,000 to $150,000, depending on the space you convert and whether you add a bathroom.
At GreatBuildz, we help California homeowners plan JADUs, ADUs, and garage conversions every week, and match them with vetted general contractors to build them. This guide covers the state rules, how a JADU compares with an ADU, what it costs, and what changes from Los Angeles to San Diego to the Bay Area.
What Is a Junior ADU?
A JADU is a separate living unit carved out of your existing house. California law allows one on any lot zoned for a single-family home, with a house that’s already there or being built. The most common versions:
- A spare bedroom (or two) walled off from the rest of the house, with a new exterior door and a kitchenette.
- An attached garage converted into a studio or small one-bedroom. An attached garage counts as part of the house, so it qualifies. A detached garage does not; that would be an ADU.
- New space, if you’re building a new house or an addition and plan the JADU into it from the start.
500 square feet is enough for a large studio or a small one-bedroom. The limit is measured as interior livable space: bedrooms, bathrooms, the kitchen, closets, and laundry areas all count.
JADU Requirements in California (2026)
These are state rules, so every California city has to allow a JADU that meets them.
- Size: 500 square feet of interior livable space, maximum. Unlike some ADU conversions, a JADU doesn’t get an extra 150 square feet for an entry.
- Location: entirely within the walls of a single-family house, including an attached garage. One JADU per lot.
- Entrance: its own entrance, separate from the main entrance of the house. If the JADU shares a bathroom with the house, it also needs an interior door into the main living area.
- Kitchen: an efficiency kitchen with a cooking appliance, a food-prep counter, and storage cabinets of reasonable size for the space. Cities can’t add their own rules on counter or cabinet sizes, appliance types, or gas or 220-volt hookups.
- Bathroom: its own, or shared with the main house.
- Parking: cities can’t require parking for a JADU, even when you convert an attached garage.
- Fire sprinklers: not required in the JADU if they aren’t required in the main house.
- Deed restriction: you record a deed restriction that says the JADU can’t be sold separately from the house and must stay within the state’s size and use rules.
- Rentals: any rental has to be for more than 30 days. No short-term rentals.
- Approval: once your application is complete, the city must approve or deny it within 60 days. The city has 15 business days to tell you whether the application is complete.
AB 1154 and Owner-Occupancy
If your JADU has its own bathroom, you don’t have to live on the property. AB 1154, effective January 1, 2026, changed the old rule that required the owner to live in either the main house or the JADU. Now:
- Shared bathroom: the owner must live in either the main house or the JADU.
- Own bathroom: no owner-occupancy requirement. You can rent out both the house and the JADU.
- Exceptions: owner-occupancy can’t be required when the owner is a government agency, land trust, or housing organization.
AB 1154 also added the rule that JADU rentals must be for more than 30 days. If you’re planning to rent the house and the JADU, it’s worth budgeting for a private bathroom. It costs more to build, but it removes the owner-occupancy rule.
JADU vs ADU: What’s the Difference?
A JADU is smaller, has to be inside the house, and is cheaper to build. An ADU can be much larger and can be detached. Here’s how they compare under state law:
| JADU | ADU | |
|---|---|---|
| Maximum size | 500 sq ft | Up to 1,200 sq ft detached; cities must allow at least 800 sq ft |
| Where it goes | Inside the house, including an attached garage | Inside the house, attached, detached, or in a detached garage |
| Kitchen | Efficiency kitchen | Full kitchen |
| Bathroom | Own or shared with the house | Must have its own |
| Owner-occupancy | Only if it shares a bathroom | Not required |
| Parking | Can’t be required | Often can’t be required (for example, near transit or when converting a garage) |
| Impact fees | Exempt | Exempt up to 750 sq ft; larger ADUs pay a proportional fee |
| Sold separately | No | Only where a city has opted in to condo-style sales |
| Typical cost | $50,000 to $150,000 | $120,000 to $150,000 for a garage conversion; $150,000 to $400,000 detached (Los Angeles) |
Choose a JADU when you have unused space inside the house and want the lowest-cost way to add a unit, for a family member, a caregiver, or a long-term tenant. Choose an ADU when you want more room, a fully separate home, or a unit you can rent without any owner-occupancy question. You can have both: on a single-family lot, state law allows a JADU plus an ADU, so a property can end up with three units.
How Much Does a JADU Cost?
Most JADUs cost $50,000 to $150,000. The range is wide because the projects are so different. Turning a spare bedroom into a JADU that shares the hall bathroom is a small job. Converting an attached garage means building a new wall where the garage door was, plus insulation, windows, a kitchenette, usually a bathroom, and new plumbing and sewer lines.
| JADU project | Typical cost |
|---|---|
| Bedroom or interior conversion, sharing the main bathroom | $50,000 to $80,000 |
| Interior conversion with its own new bathroom | $70,000 to $110,000 |
| Attached garage conversion | $70,000 to $120,000 |
| Garage conversion with high-end finishes or major plumbing, sewer, or electrical upgrades | Up to about $150,000 |
Plans from a designer or architect usually add $4,000 to $10,000. The things that push a JADU to the high end are adding a bathroom far from the existing plumbing, upgrading an electrical panel, and finish choices. Because JADUs are exempt from impact fees, city fees are lower than for a comparable ADU. For a full-size ADU budget, see our guide to the cost to build an ADU in Los Angeles, and for ways to bring the number down, our ADU cost-saving tips.
How to Build a JADU
- Check your property. Confirm the space is inside the house (or an attached garage), that you can add a separate entrance, and that your plumbing, electrical panel, and sewer line can handle another unit. Our team offers a free 15-minute call to help with this.
- Get plans drawn. A designer or architect prepares plans for the city’s plan check. Expect $4,000 to $10,000.
- Meet contractors early. While plans are in progress, have two or three experienced contractors look at the space and the plans. They’ll catch problems with utilities, layout, or cost before you submit. Our ADU/JADU construction checklist helps you get bids that compare.
- Submit for permits. The city has 15 business days to confirm your application is complete and 60 days after that to approve or deny it.
- Pick your contractor and build. Once plans are final, contractors give detailed bids. Construction itself usually takes two to three months.
From first plans to move-in, most JADUs take about three to six months.
JADU Rules by Region
State law sets the floor everywhere, but who issues your permit and what local issues come up differ.
Los Angeles
In the City of Los Angeles, the Department of Building and Safety (LADBS) issues JADU permits. Properties in Historic Preservation Overlay Zones (HPOZs), hillside areas, or high fire hazard zones can face extra review, so check your zoning early. JADU plans also have to meet the state’s Title 24 energy code. One LA-specific issue is rent control: if your house was built on or before October 1, 1978, adding a JADU can bring the house under the city’s Rent Stabilization Ordinance. A JADU converted from non-habitable space, like a garage, generally falls under the city’s Just Cause Ordinance instead. The LA Housing Department explains how each case works.
Orange County
Each Orange County city issues its own permits and has its own ADU ordinance, so the process in Irvine looks different from Huntington Beach. State law still controls the basics: 500 square feet, no parking requirement, and no owner-occupancy requirement when the JADU has its own bathroom. Many OC homes are in HOAs. An HOA can’t prohibit a JADU, but it can set reasonable rules, so check your CC&Rs.
San Diego
Inside city limits, the City of San Diego’s Development Services Department handles JADU permits. In unincorporated San Diego County, it’s the County’s Planning & Development Services. Other cities, like Chula Vista or Oceanside, use their own building departments. Our San Diego ADU page covers the local process in more detail.
Bay Area
Every Bay Area city runs its own permit office, and older housing stock means more surprises: undersized electrical panels, old sewer laterals, and historic district reviews. Before you commit, have a contractor check the panel, plumbing, and sewer line, figure out where a separate entrance can go, and confirm whether your house is in a historic district. Cities can’t require parking for a JADU or set a size limit below 500 square feet, even if an older local ordinance says otherwise.
Financing a JADU
Many homeowners pay for a JADU from savings because it’s the least expensive unit you can add. Others use a HELOC, a home equity loan, or a renovation loan. Our California ADU financing guide compares every option.
Why Homeowners Build JADUs
The reasons vary. Some create a private space for an aging parent or a grown child. Some retirees move into the JADU and rent the main house. Others rent the JADU for extra income; in Los Angeles, a studio or small one-bedroom JADU can rent for roughly $1,500 to $2,000 a month, depending on size, location, and finishes. Our guide to renting an ADU has more on rents.
If you plan to rent it, give it a good entrance, storage, and laundry if you can fit it, since those help rents. Call your insurance agent to add the JADU to your policy. And don’t cut corners on construction; a poorly built unit is hard to keep rented.
Other ADU Laws to Know
State ADU law changes almost every year: rules on unpermitted units, multifamily ADUs, pre-approved plans, and condo-style ADU sales have all changed recently. We keep those in one place in our guide to new California ADU laws.
How to Find a JADU Contractor
Hire a licensed general contractor who has built ADUs, JADUs, or garage conversions in your city. A handyman isn’t licensed or equipped for this kind of work. Before you hire:
- Check the license on the Contractors State License Board site to confirm it’s active, has no disciplinary actions, and shows workers’ compensation insurance if the contractor has employees.
- Get a copy of their liability insurance certificate.
- Call at least three references, and read their online reviews, especially the negative ones.
- Get bids from at least three contractors using the same scope checklist, and compare them line by line. Some include finish materials and some don’t.
For more, see our 10 tips for hiring an ADU contractor.
Frequently Asked Questions
What is a JADU?
A JADU, or junior accessory dwelling unit, is a unit of up to 500 square feet built entirely inside a single-family house, including an attached garage. It needs its own exterior entrance and an efficiency kitchen, and it can have its own bathroom or share one with the main house.
Do you have to live on the property with a JADU?
Only if the JADU shares a bathroom with the main house. Under AB 1154, effective January 1, 2026, a JADU with its own bathroom has no owner-occupancy requirement, so you can rent both the JADU and the house. When the rule applies, the owner can live in either the house or the JADU.
What’s the difference between an ADU and a JADU?
A JADU is limited to 500 square feet and must be inside the existing house, with an efficiency kitchen and an optional shared bathroom. An ADU can be up to 1,200 square feet, can be detached, and must have a full kitchen and its own bathroom. JADUs cost less to build and are exempt from impact fees.
Can I build both an ADU and a JADU on my property?
Yes. On a single-family lot, state law allows one JADU plus an ADU, so the property can have three units including the main house. The JADU’s owner-occupancy rule applies only if it shares a bathroom with the house.
Can I convert my garage into a JADU?
Yes, if the garage is attached to the house, since an attached garage counts as part of the home. A detached garage can’t be a JADU, but it can be converted into an ADU. The city can’t require you to replace the lost parking.
How much does a JADU cost in California?
Most JADUs cost $50,000 to $150,000. A bedroom conversion that shares the main bathroom typically runs $50,000 to $80,000, an interior conversion with its own bathroom $70,000 to $110,000, and an attached garage conversion $70,000 to $120,000, with high-end finishes or major utility upgrades pushing it toward $150,000.
Can my HOA stop me from building a JADU?
No. California law doesn’t let an HOA prohibit a JADU or ADU on a single-family lot, though it can apply reasonable rules that don’t make building one unreasonably costly or difficult.
Can I legalize an unpermitted JADU or garage conversion?
Often, yes. You’ll need to bring the unit up to code and get it permitted. A contractor can look at the existing conversion and estimate what it will take. For units built before 2020, state law offers a path to legalize them based on health and safety standards.
Does adding a JADU make my house subject to rent control?
In the City of Los Angeles, it can. If your house was built on or before October 1, 1978, adding a JADU can bring the house under the Rent Stabilization Ordinance. A JADU converted from a garage or other non-habitable space generally falls under the Just Cause Ordinance instead. Check the LA Housing Department’s ADU page for your situation.
Will my property taxes go up if I build a JADU?
Most likely, yes, but only for the new construction. The assessor adds the value of the JADU to your assessment without reassessing your existing home.
Can I rent my JADU on Airbnb?
No. State law requires JADU rentals to be for more than 30 days, so short-term rentals aren’t allowed.
Ready to talk about a JADU for your home? GreatBuildz is a free service that matches California homeowners with three vetted general contractors and stays involved through the project. Call us at 818.317.3567 or get matched here.
