ADU vs JADU: Key Differences

Key Takeaways

An ADU, or accessory dwelling unit, is a fully independent living space that sits on the same property as the primary residence. It can be attached to a single-family home or be an entirely detached structure.

A JADU, or junior accessory dwelling unit, is an independent living space that’s built within the confines of the existing home. For example, a homeowner could convert an attached garage or extra bedroom into a studio apartment, and that would be considered a JADU since it doesn’t extend the home’s footprint.

Though both ADUs and JADUs can be used as granny flats, rental units, or apartments for adult children, there are different regulations and building codes to keep in mind, including:

• Size: An ADU can often be as large as 1200 square feet, while a JADU can only be 500 square feet.
• Kitchen requirements: ADUs require a full kitchen with a stovetop, fridge, counter space, and cabinets. A JADU only requires an efficiency kitchen with plug-in cooking appliances like hot plates and toaster ovens in lieu of a stove.
• Bathroom requirements: ADUs require their own bathroom. JADUs can share a bathroom with the main house.
• Rental regulations: ADUs can be rented even if the property owner doesn’t live in the main home. JADUs can only be rented if the property owner lives on-site.

Framing layout can determine if the build qualifies as an ADU with its own footprint—key to understanding the space, utility routing, and compliance needs from the outset.

What Are ADUs and JADUs?

An accessory dwelling unit, or ADU, is an independent living space that sits on the same property as a single-family home. ADUs can take many forms and can include attached ADUs, which are added onto and share a wall with the main residence, detached garage conversions, or traditional backyard cottages.

To be considered an ADU, a living space must contain:

• A kitchen
• A bathroom
• A separate entrance (in most cases)

JADUs are separate living spaces built within the boundaries of an existing home. Essentially, a homeowner takes an unused space, like an extra bedroom, attic, or basement, and converts it into an efficiency apartment. JADUs must contain a kitchenette and have a separate entrance. They don’t have to have their own bathroom (though having one does improve rental potential, if you plan to use your JADU to generate additional income).

Detached ADUs like this one maximize privacy and function, ideal for long-term rentals or multigenerational living—offering more flexibility than JADUs confined to existing structures.

Differences Between ADUs and JADUs

Aside from having different footprints, ADUs and JADUs also differ in terms of overall size and requirements, especially when it comes to kitchen, bathroom, parking, and owner-occupancy.

It’s important to know that while ADUs and JADUs have different requirements for owner occupancy when it comes to rentals, Southern California prohibits short-term rentals for both build types, meaning both ADUs and JADUs can only be used for long-term rentals.

Benefits of ADUs vs JADUs

Adding either an ADU or JADU to your property can significantly increase your property value. Both can also be used as in-law suites, guest houses, or even rental units. Which build you choose (ADU or JADU) will often depend on your lot size, intended use, and overall budget.

Advantages of Building an ADU

ADUs offer homeowners the edge when it comes to flexibility. Typically, ADUs are larger than JADUs, and since they must contain both a full kitchen and bathroom, they can have a multitude of uses throughout their lifetime. An ADU can be built as a way of housing family, for example, but in the future, it can easily be converted into a rental property or a home office.

Because ADUs are larger and typically more private than JADUs, they also tend to generate higher rental income.

Advantages of Building a JADU

JADUs are typically more cost-efficient than ADUs, given their smaller size and the fact that the exterior structure (aka the main house) is already built. If you don’t choose to include a bathroom in your JADU, this also saves money on plumbing and fixtures.

JADUs also tend to have a quicker permitting process, allowing homeowners to have extra living space on their property in less time and for less money.

Interior features like full kitchens and separate living areas boost rental appeal and ROI—one of the top benefits of choosing an ADU over a JADU.

Legal and Zoning Considerations

The good news is that because both ADUs and JADUs are seen as a way to combat the state’s housing crisis and provide more affordable housing options, both are highly incentivized throughout Southern California. With an experienced ADU/JADU builder, the permitting process can be smooth with either build, though there are different considerations when it comes to zoning.

Permitting Process

Over the past several years, laws have been put in place to make the permitting process for both ADUs and JADUs as easy as possible.

For example, California’s 60-Day Law requires that the building department either approve or deny a permit for an ADU or JADU within 60 days of receipt.

Although the overall response time still varies from city to city, JADUs typically have faster response times, as there’s less for the building department to consider; JADUs are simpler builds.

Zoning Differences

AB 2221 prevents local municipalities from establishing zoning laws that make it overly burdensome for property owners to build an ADU or JADU on their property. For example, cities can’t require setback requirements of greater than 4 feet for ADUs.

Given that JADUs are being built within an existing structure, though, there are typically fewer zoning laws to consider. Also, unlike ADUs, JADUs aren’t subject to homeowner’s association regulations since they don’t affect the outward appearance of the existing home.

Permit success starts with professionally drafted blueprints—an essential tool for navigating the 60-Day Law and ensuring code-compliant design under AB 2221.

Cost and ROI Comparison

While more expensive to construct, ADUs often have greater ROI than JADUs.

Construction Costs for ADUs

ADUs can cost homeowners anywhere from $150,000 to $200,000 for a garage conversion to $400,000+ for a new, detached ADU. Along with the style of ADU (attached, detached, or garage conversion), overall size and finishings also affect the construction budget. Larger size ADUs with high-end finishings can easily get homeowners to that $400,000 range.

Most homeowners find that the initial costs are worth it, though, as ADUs can increase property value by as much as 35%. There are also several financing options available for ADUs.

Construction Costs for JADUs

Because they’re typically smaller and don’t require full kitchens or bathrooms (and all the costs associated with them), JADUs can often be built for anywhere between $50,000 and $100,000.

This investment does come with an ROI, though it isn’t as substantial as with a detached ADU.

Property Tax Implications

Both ADUs and JADUs can increase your property taxes, though in most cases, this increase is outweighed by the overall increase in property value.

Neither build triggers a full property reassessment. Instead, the cost of the build is added to the current taxed value of your existing property to determine your new taxable rate. You can read more about partial assessments here.

ADUs require more upfront investment but yield higher returns—especially when built as standalone units with premium finishes and thoughtful layouts.

How to Choose Between an ADU and a JADU

Generally, JADUs are ideal for homeowners looking for a faster, cheaper, and simpler build, while ADUs offer greater ROI, flexibility, and rental income.

A JADU may be the ideal choice if you:

• Want a lower cost project (under $100K)
• Have unused space within your existing home
• Have a small lot with limited building opportunities
• Want a faster approval process
• Plan to live on the property for the long term
• Want to use the JADU as an in-law suite or an apartment for adult children
• Want minimal disruption to the home’s exterior during construction
• Have strict HOA requirements

An ADU may be the ideal choice if you:

• Have a bigger construction budget
• Want to build a completely separate, private structure
• Have adequate lot space
• Want the option to rent out the ADU and the primary home
• Want to maximize rental income
• Want to maximize flexibility when it comes to design & use

When space is tight, a JADU conversion like this offers a budget-friendly solution with fewer permitting hurdles—ideal for homeowners staying long-term.

Maximize Your Space with Better Place Design & Build

At Better Place Design & Build, we have extensive experience building beautiful, functional ADUs and JADUs that meet homeowners’ needs in the short term while maximizing their ROI in the long term.

Not sure whether an ADU or JADU is right for you? We can help. After hearing more about your budget and goals, we can help guide you in the right direction and provide you with a proposed cost, timeline, and design—all at no cost to you. Get in touch to schedule your free consultation today.

Leveraging existing structures like side yards for JADUs can save time and money—Better Place Design & Build helps you determine the smartest fit for your lot and goals.