What Is a Junior ADU? Advantages & Disadvantages

May 30, 2022 | ADU

Additional dwelling units (ADUs) have become powerful tools for homeowners to gain extra living space on their property. An ADU can be a great way to bring in extra income, house family members, or use it as a personal office. We know what an ADU is, but what is a junior ADU?

As a general rule, a Junior ADU (JADU) is a secondary unit no larger than 500 square feet located on the same lot as a single-family home. It differs from ADUs in several ways other than size. 

There are many advantages and disadvantages to constructing a JADU on your property. Whether building one is right for you depends on your budget, location, and what you plan to do with it. Read on to learn important concepts about JADUs and their differing legal definitions.


JADU Explained

Various important ways differentiate a Junior ADU from an ADU. If you would like to look at California’s state building code that lays out exactly what a JADU is, you can do so here. However, if legal jargon is not your thing, we have summarized the key concepts below.

  • Can be a maximum of 500 Ss. ft. and a minimum of 150 sq. ft.
  • Can be built on the same property as an ADU
  • Can share a bathroom with the residence
  • Either JADU or single-family residency must be owner-occupied
  • Have fewer utility separation requirements than ADUs
  • Must be attached to the primary residency
  • Must be contained with a single-family residence (in other words, on the property of your single-family home)
  • Must have its own entrance/exit (you have to be able to enter from outside not just from within your home)
  • Needs its own kitchen (efficiency kitchen)
  • There is no parking required


Comparing ADUs To JADUs

If the key concepts laid out above aren’t enough, here is a chart comparing ADUs to JADUs to help you understand the key similarities and differences.

Parameter ADU JADU
Size Max 1,200 sq ft* Max 500 sq ft
Location Attached or detached Attached
Parking Depends on location No
Kitchen Full size or kitchenette Efficiency kitchen
Bathroom Separate Separate or shared
Owner Occupancy Requirements No Yes

* ADU size limits vary by jurisdiction but are always no more than 1,200 sq. ft.


JADU Definitions Can Vary

As we have seen with ADUs, different cities and counties can create their own regulations surrounding JADUs. These regulations can conflict with the definitions laid out above but generally follow the same idea.

The main conflicting definition that jurisdictions have is whether homeowners can convert pre-existing non-livable space (like an attached garage) into a JADU or only existing livable space (like a bedroom). However, there are quite a few other conflicting definitions as well.

Some other varying definitions include whether a JADU can be built attached to an ADU on the property instead of to the primary residency and whether the homeowner can build outside the footprint of the residence for the 150 square foot bump out for ingress/egress. State code has provided more concrete answers to many of the other ways cities have created varied definitions, but cities/counties can still find ways around those definitions.


How Do Jurisdictions Regulate JADUs?

Some people might ask how cities/counties can have differing definitions of JADUs than the state code. This is a common question about ADUs as well.

There are two main ways cities/counties can have differing JADU definitions. They can interpret/enforce the state code in different ways or pass ordinances to restrict it.

Ordinances are a local law that allows the local jurisdiction to forbid or restrict something. So, for a JADU, the local government might require you to follow strict zoning laws that do not allow you to add on a JADU under the setback requirements.

If ordinances are not in place, the local planning board can interpret the law differently than the neighboring county, meaning it will be enforced differently. A great example of this is whether a garage is included in a single-family residence.


Knowing Your Junior ADU Definition

With so many varying definitions of what constitutes a Junior ADU, it can be tough to know what rules you need to follow. To start, you need to figure out what jurisdiction you fall under. An easy way to do this is to peek at your address and see what city/county you live in. Next, head online to your local government’s website and search for their JADU guidelines.

If you are struggling to find what you need, you can always go to your local planning board and ask them directly what you need to know to build a JADU. You can also work with an ADU expert who can do all the hard work of figuring out what JADU regulations apply to you.


Advantages Of JADUs

One of the biggest advantages of a Junior ADU is the fact that it is more affordable to develop than an ADU due to its size. However, there are a number of other advantages to developing a JADU including:

  • Adding living space square footage if the jurisdiction allows it
  • Avoiding impact fees
  • In some jurisdictions, JADUs don’t require building or fire code upgrades which saves you money during the permitting process
  • Sharing sanitation and utilities makes it easier to build and more affordable
  • You can develop a JADU in addition to an ADU, creating a triplex on your single-family residency to bring in more rental income

Of course, you also benefit from all the advantages of having an ADU in general like multi-generational housing, rental income opportunities, and increased resale value of your property. You can also partake in house-hacking by living in your JADU and renting out the primary home to pay off your mortgage quicker. This is done since renting a full house brings in more income than renting out a JADU.


Disadvantages Of JADUs

There are also disadvantages to developing a JADU that may dissuade some people from undergoing JADU development. They include things like:

  • Owner occupancy regulations that require you to live within the JADU or primary residence
  • Permitting costs that make it more expensive than just simply renting out a spare bedroom in your home
  • The fact that you can’t build it more than 500 sq. ft.

As with any ADU, there is also the disadvantage of having to have a kitchen and bathroom if you want to use the JADU for something other than as an additional living space (i.e., office or gym). There is also the problem that it must be at least 150 Sq. Ft. Some people want to try to build things smaller than this because they feel they don’t need that much space. The only way to do so would be to apply for a discretionary permit, but those are rarely granted.


Should You Develop a Junior ADU?

If you are considering developing an ADU yourself, you may be wondering whether you should build a JADU or a conventional ADU. You might even be considering if you need to develop an additional dwelling unit at all. To help you decide what is the right choice for you, you should ask yourself these important questions.

  • Do you have an attached garage you don’t use often? If yes, doing a garage conversion into a JADU could save you time and money.
  • Do you have a pre-existing detached ADU? If yes, you can consider (if your city/county allows) attaching your JADU to that to bring in more rental income.
  • Do you plan to live in either the JADU or primary home? If you don’t plan to live in either, a JADU will not be possible for you.
  • Do you think you will need more than 500 sq. ft. of space? If yes, a JADU is not for you.

Essentially, if you plan to build an ADU, the deciding factors of whether it should be a JADU or conventional ADU are your size requirements and budget. If you want to save as much money as possible, a JADU is probably the way to go since they can have shared utilities and bathrooms.


Cost of Developing A JADU

As many of you know, the cost of Developing an ADU varies immensely based on your design tastes, type, and materials used. The same goes for a Junior ADU. The amount you pay for your JADU development could be immensely different from the amount your neighbor pays.

As with any ADU, the four main cost factors of a JADU are:

  • Design and planning
  • City fees
  • Construction labor and material
  • Finish materials

Your design tastes and the size of your JADU will greatly impact the cost of your design and planning phase. Who you choose to construct your JADU and where you buy materials from (and the quality of the materials) will greatly impact construction labor and material costs. Finish material costs are also completely dependent on the quality of materials you choose. However, the city fees phase is a constant that you can control.


JADU Cost Ranges

We can’t give you an exact average of how much your JADU will cost since there are so many variable factors. However, you can expect to pay anywhere from $20,000 to above $100,000.

A $20,000 JADU is not common. This occurs if you are lucky enough to have a room with an existing outside door that just needs an efficiency kitchen added and city fees paid. However, this is not the case for most people.

Most people are trying to add square footage to their homes. Adding an attached unit means preserving the existing unit while trying to adjust it to support a new, attached unit. It will likely be just as expensive as building a detached ADU of the same square footage. The same goes if you are attaching your JADU to an ADU. It will likely have a similar cost per square foot.

You can check out this garage conversion cost calculator or this ADU cost calculator to get a general idea of how much your JADU construction will cost.


Don’t Forget About Appliances

A big thing you need to remember when building your JADU is that once it is built, you are not done. You still need to install ADU appliances and furniture. This includes things like:

  • Bedroom furniture
  • Furniture for dining areas
  • Kitchen gadgets
  • Living space furniture
  • Possibly HVAC systems

So, be sure that is included in your budgeting plans before you commit to building the JADU.


Budget Your JADU

Speaking of budgeting, make sure you properly budget out your JADU before you begin construction. One of the biggest ADU mistakes you can make is starting a project without budgeting it out properly beforehand.

A budget allows you to paint a more accurate picture of your expected costs. It also keeps you from acquiring any unnecessary costs that lead to overspending. Not to mention, it also helps you know how much money you need to take out in loan form or draw from your savings.


Alternatives You Should Know

A Junior ADU isn’t for everyone. If you decide it isn’t going to meet your needs, you should be aware of these two main alternatives.


Rent A Room in Your House

If you are looking to make rental income but don’t want to jump through all the hoops of developing a JADU, you may be able to simply rent a room out of your house. If you have a permitted, finished room, you can rent it out long term in most cases.

The only thing you need to watch out for is if your mortgage agreement forbids it or if you are in a covenant that forbids long-term rentals. Sometimes HOAs prevent individuals from renting rooms out in their homes long-term.


Build A Conventional ADU

If the size restrictions of a JADU don’t allow you the space you need, you should consider building a conventional ADU. A conventional ADU has no owner-occupancy requirements and can be attached, detached, or a conversion.

An ADU gives you more flexibility with what you can do with your unit in terms of design (since it doesn’t need to be attached and there is more space). Also, potential renters will be more interested in a larger space that has its own bathroom facilities (tip: include a laundry unit in your ADU to keep renters happy as well). In smaller JADU he limited space makes it hard to have its own bathroom and the extra living space an ADU can offer.


Start Developing Your JADU Today

Is a Junior ADU something you are interested in developing in your single-family residency? Check out this free ADU development guidebook to learn more about ADUs in general and then start your free consultation with Levi Design Build to go over all the steps you need to complete your JADU project.

We will take the time to answer all your JADU questions and figure out what the regulations are in your jurisdiction. Together, we can compare the pros and cons of developing a JADU over the development of a conventional ADU and help you with your ADU financing. You will have access to a team of design, planning, and construction professionals with years of experience developing JADUs that fit your unique needs.

Contact us today to get started on your dream Junior ADU.