Junior ADU 2023: Types, Benefits, Costs & More

Sep 12, 2023 | ADU

Junior ADU Explained

The concept of accessory dwelling units (ADUs) has gained significant traction in recent years as an innovative solution to address housing shortages, promote sustainable urban development, and provide flexible housing options. In California, this trend has been further diversified by the introduction of junior accessory dwelling units (JADUs). While both ADUs and JADUs serve to increase housing supply and offer flexibility, they differ in terms of their characteristics, requirements, and applications.

ADUs have emerged as valuable resources for homeowners seeking to expand their living space within their properties. An ADU presents an excellent opportunity to generate supplementary income, provide accommodation for relatives, or establish a dedicated personal workspace. While the concept of an ADU is familiar, with that it seems that junior ADUs (JADU) are not as familiar and understood by homeowners.

The development of a JADU on your property offers a range of benefits and drawbacks. Deciding whether it’s a suitable endeavor hinges on factors like your financial resources, the property’s location, and your future use for the unit. In this article we will review key insights about JADUs and their distinct legal definitions.

Quick review of what is an ADU

An Accessory Dwelling Unit (ADU) is a self-contained living unit that is either attached to or located on the same lot as a primary dwelling unit. ADUs can take the form of converted garages, separate cottages, or additions to an existing home. The primary purpose of ADUs is to provide additional housing options within established residential neighborhoods, without the need for major changes to local infrastructure. ADUs can be rented out or used to accommodate family members, providing a flexible solution for homeowners and renters alike.

In California, ADUs have gained prominence due to the state’s policy changes aimed at reducing housing shortages. Legislative reforms have led to relaxed regulations, making it easier for homeowners to construct and rent out ADUs. These reforms have included adjustments to minimum lot sizes, parking requirements, and permitting processes, allowing more property owners to take advantage of the benefits that ADUs offer.

Junior ADU Types, Benefits, Costs & More

What is a Junior ADU (JADU)?

Junior Accessory Dwelling Units (JADUs) are a subgroup of ADUs that are smaller and simpler in design. A JADU is created by converting a portion of an existing primary dwelling, such as a bedroom, into an independent living space with its own entrance, bathroom (can also be shared with main house), and kitchenette facilities.

Unlike traditional ADUs, JADUs do not require additional exterior construction and are often seen as an ideal solution for homeowners seeking to maximize their property’s utility without major structural changes.

These units are intended to provide an affordable housing solution for singles, couples, and small families. JADUs are subject to specific regulations outlined by state law, aimed at ensuring they remain relatively small and do not compromise the character of neighborhoods. These regulations cover various factors such as size, location, and the number of bedrooms within a JADU.

Key Differences and Benefits of Junior ADU:

Should you wish to review California’s ordinance that defines a JADU, you can access it through this link. Nevertheless, we have summarized the essential notions below for your convenience.

  1. Size and Design: The most significant difference between ADUs and JADUs is their size and design. While ADUs are standalone living units that can range in size from 150-1,200 Sqf, JADUs are smaller and are created by converting existing space within a primary dwelling and limited to 500 Sqf.
  2. Construction: ADUs often require more extensive construction, involving either repurposing existing structures or building new ones on the property. In contrast, JADUs involve minimal exterior construction, focusing on converting interior space.
  3. Cost: Due to their simpler design and construction, JADUs typically cost less to create than traditional ADUs, making them an attractive option for homeowners with budget constraints.
  4. Regulations: Both ADUs and JADUs are subject to regulations to maintain community aesthetics and ensure safety. However, JADUs have specific regulations tailored to their unique characteristics.
  5. Housing Diversity: JADUs cater to a different demographic, providing housing options for individuals or small households. ADUs offer more flexibility in terms of the types of occupants they can accommodate.
  6. Owner Occupancy: a junior accessory dwelling unit requires an owner occupancy deed restriction. This means you can only rent out your JADU if you live in the existing house as your primary residence (alternatively, you can live in the JADU and rent out the main house).

Additional basic requirement:

  • Have fewer utility separation requirements than ADUs, can share utilities with main house.
  • Must be attached to the primary residency with a door connecting between them.
  • Must have its own entrance/exit, allowing access from outside rather than exclusively within the home.
  • Must include an independent kitchenette, designed as an efficiency kitchen.


Here is comparative chart illustrating the key resemblances and distinctions between ADUs and JADUs to aid with comparing between the two.

Size Max 1,200 SqfMax 500 Sqf
Location Attached or Detached Attached
New Construction Allowed Yes No*
Parking Depends Location & Situation No
Utilities SeparateShared
Kitchen Full Size or KitchenetteEfficiently Kitchen
ParkingDepends on locationNot Required
BathroomSeparate Separate or Shared
Owner Occupancy NoYes
City Application Fees Thousand $$$Hundreds $$

*Add on of 150 Sqf for ingress and egress is allowed.

*Building a home addition that later can be asked to be converted to JADU is also optional with creative ADU planning.

Junior ADU Classification and Interpretations

Just as with the case of ADUs, different municipalities and counties have the authority to establish their own regulations governing JADUs. While these regulations might conflict from the definitions outlined earlier, they generally adhere to the core concept.

The primary area of discrepancy in definitions across jurisdictions revolves around whether property owners can transform pre-existing non-livable spaces (like an attached garage) into JADUs, or if the conversion is limited to existing livable areas (such as bedrooms). However, multiple other areas of conflicting interpretation exist.

Other contrasting interpretations encompass whether a JADU can be constructed in association with an ADU on the property rather than being connected to the primary residence. Additionally, there is debate about whether homeowners can extend beyond the residence’s existing footprint for the 150 square foot expansion required for ingress/egress. While state codes have provided clearer answers to several other instances where varying definitions were created by different cities, municipalities and counties can still discover ways to deviate from those defined standards.

How Do Cities and Counties Regulate JADUs?

A common inquiry that arises concerns the variance between city/county definitions of JADUs and those outlined in state code. This question mirrors a frequently asked question about ADUs as well.

The difference in JADU definitions across different municipalities or counties can be attributed to two primary factors.

First, there’s the potential for distinct interpretation and enforcement of the state code.

Second, local ordinances can be introduced to impose limitations.

Local ordinances function as regional laws that empower local jurisdictions to either prohibit or restrict certain activities. In the context of JADUs, a local government might implement stringent zoning regulations that prevent the addition of a JADU due to setback requirements.

In the absence of such ordinances, differences in enforcement can arise when local planning boards interpret laws differently from neighboring counties. A notable illustration of this is the determination of whether a garage should be considered part of a single-family residence.

Knowing Your Junior ADU Potential

In the face of the multitude of interpretations for what constitutes a Junior Accessory Dwelling Unit (JADU), understanding the regulations you must adhere to can be confusing. To initiate the process, your foremost task is to determine the jurisdiction you fall under. A convenient approach is to inspect your address, identifying the city or county in which you reside. Following this, search your local government’s website ordinance, where you can uncover the specific JADU guidelines they have laid out.

Should you encounter difficulty in your search, there’s always the option to meet with your local planning department. By communicating directly with them, you can gain clarity on the necessary information to develop a JADU in line with regulations. Alternatively, you can look for the assistance of an ADU/JADU expert, who can take on the to conduct a feasibility study for your JADU.

Junior ADU Types, Benefits, Costs & More

Benefits and Drawbacks of Junior ADUs (JADUs)

A Junior Accessory Dwelling Unit (JADU) offers several notable advantages, stemming primarily from its compact size. Here are some key benefits associated with developing a JADU:


JADUs are essentially more cost-effective to construct compared to traditional ADUs due to their smaller footprint. This affordability factor extends to various aspects of the development process.

Increased Living Space:

In jurisdictions that permit it, JADUs enable the expansion of living space square footage within your property, providing additional room for various needs.

Avoiding Impact Fees:

JADUs can often bypass impact fees, leading to financial savings during the development phase.

Regulatory Savings:

In select jurisdictions, JADUs might be exempt from certain building and fire code upgrades, resulting in reduced expenses during the permitting process.

Shared Utilities:

The ability to share sanitation and utilities between the primary residence and the JADU streamlines construction and minimizes associated costs.

Combining with ADUs:

It’s possible to construct a JADU alongside an ADU, effectively transforming your single-family residence into a triplex. This arrangement allows for increased rental income potential.

General ADU Advantages:

JADUs encompass all the advantages that standard ADUs offer, such as catering to multi-generational housing needs, generating rental income, and augmenting the resale value of your property.

House-Hacking Opportunity:

A unique advantage lies in the potential for “house-hacking.” By residing in the JADU while renting out the primary home, you can expedite mortgage payment. Given that renting an entire house often yields higher income than renting a JADU alone, this strategy can contribute to financial efficiency.

While Junior Accessory Dwelling Units (JADUs) offer numerous benefits, there are certain disadvantages that might discourage some individuals from pursuing JADU development. These include:

Owner Occupancy Requirements:

Many jurisdictions impose regulations that mandate either the homeowner’s residence within the JADU or the primary residence. This can limit flexibility for property use.

Size Limitation:

JADUs are typically restricted to a maximum size of 500 square feet. This limitation might not align with the preferences or needs of individuals seeking more substantial living spaces.

Minimum Size Requirement:

JADUs must meet a minimum size requirement of 150 square feet. This stipulation might conflict with the preferences of those desiring smaller living spaces.

In summary, the benefits of JADUs hold financial savings, expanded living space, and the potential for innovative housing strategies that cater to various lifestyle and investment goals.

Where, the drawbacks associated with JADUs encompass regulatory limitations, and size constraints that might not align with individual preferences or needs. Potential JADU developers should carefully weigh these disadvantages against the benefits to determine the best course of action.

Making the Choice: Developing a Junior ADU

As you weigh the prospect of creating an Additional Dwelling Unit (ADU), you might be faced with the question of whether a Junior ADU (JADU) is the right fit for your needs, or if a conventional ADU would be a better option. You might even be deliberating whether building an extra dwelling unit is necessary at all. To guide your decision-making process, consider asking yourself the following questions:

  1. Do you have an attached garage or a spare bedroom that aren’t used as often and you miss if they are not part of your main home any longer? If so, converting it into a JADU could prove to be a cost-effective and efficient solution.
  2. Are you planning to reside in either the JADU or the primary residence? If neither of these living arrangements is in your plans, pursuing a JADU might not be a feasible option.
  3. Do you anticipate requiring more than 500 square feet of space? If your needs surpass this threshold, a JADU might not fulfill your requirements.

In essence, if you’re set on constructing an ADU, your choice between a JADU and a traditional ADU hinges on factors like your size requirements and financial considerations. Opting for a JADU could be advantageous if you aim to minimize expenses, as these units can share utilities and bathrooms, ultimately saving you money.

Ultimately, your decision should be based on your specific circumstances, size requirements, and budgetary considerations. Careful evaluation of these factors will guide you towards the optimal choice between a JADU and a conventional ADU.

Junior ADU Types, Benefits, Costs & More

Cost Considerations for Developing a JADU

The cost of developing an ADU can vary significantly based on factors such as design preferences, materials used, and the chosen construction approach. This variability is equally applicable to Junior ADUs (JADUs). The amount you invest in JADU development might differ significantly from your neighbors’ costs.

Like any ADU project, the primary cost components for a JADU are as follows:

  • Design and Planning
  • Municipal Fees
  • Construction Labor and Materials
  • Finishing Materials

Your design preferences and the size of your JADU will substantially influence the expenses associated with the design and planning phase. The choice of construction team and material suppliers, as well as the quality of materials used, will considerably impact construction labor and material costs. Costs for finishing materials are intrinsically tied to the materials’ quality you opt for.

Junior ADU Cost Ranges

While we cannot provide a precise average cost for your JADU due to the multitude of variables, anticipate expenses ranging from $20,000 to beyond $100,000.

A $20,000 JADU will be where an existing room possesses an exterior door and needs solely the addition of an efficiency kitchen, coupled with city fees, therefore the costs of design and planning are limited, and even more so the costs of construction.

Incorporate Appliance Costs

An essential consideration during JADU construction is the post-construction phase, which involves the installation of appliances and furniture. This encompasses items such as:

  • Bedroom Furnishings
  • Dining Area Furniture
  • Kitchen Appliances
  • Living Area Furnishings
  • Possibly HVAC Systems

It’s crucial to factor these expenses into your budgetary planning before embarking on the JADU project.

Strategize Your JADU Budget

Undertaking a project without a well-defined budget is one of the most significant mistakes in a JADU development.

A thorough budget not only provides a realistic projection of anticipated expenses but also prevents unnecessary costs that might lead to overspending. Furthermore, it aids in determining the financial resources required, whether in the form of loans or savings, for successful JADU completion.

Are You Ready To Start Your JADU Journey

Does the prospect of developing a Junior Accessory Dwelling Unit (JADU) for your single-family residence intrigue you?

Explore this FREE guidebook on ADU development for valuable insights into the process, and then initiate your no-cost consultation with us to seamlessly navigate every phase of your JADU project.

During this consultation, we’re committed to addressing all your JADU-related inquiries and demystifying the regulations applicable to your jurisdiction. Together, we’ll conduct a thorough analysis of the benefits and drawbacks associated with choosing a JADU over a traditional ADU.

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


  • What is a Junior ADU (JADU)?
    A Junior Accessory Dwelling Unit (JADU) is a type of housing unit that is smaller in size compared to a traditional ADU and is typically contained within the walls of a single-family residence. It’s designed to be more compact and can often be created by converting spaces like attached garages or spare bedrooms.
  • What are the main advantages of a JADU?
    JADUs offer benefits like affordability, increased living space, avoidance of impact fees, potential regulatory savings, shared utilities with the primary residence, and potential for higher rental income when combined with an ADU. They also present opportunities for house-hacking and cater to multi-generational housing needs.
  • Are there any limitations to developing a JADU?
    Yes, there are certain disadvantages including owner occupancy requirements, size limitations (usually a maximum of 500 sq. ft.), and a minimum size requirement of 150 sq. ft.
  • How can I determine if a JADU or a traditional ADU is right for me?
    Consider factors like available space, your living arrangements (i.e., if you plan to reside in the JADU or primary residence), and size requirements. If you have a tight budget and size needs under 500 sq. ft., a JADU might be advantageous.
  • What are the primary cost components for developing a JADU?
    Key cost components include design and planning, municipal fees, construction labor and materials, and finishing materials.
  • What is the typical cost range for a JADU?
    While costs can vary, you might expect expenses to range from $20,000 to beyond $100,000. The lower end might involve simpler additions like an efficiency kitchen, while the higher end would encompass more comprehensive renovations.
  • Should I account for appliance costs when planning a JADU?
    Yes, it’s crucial to factor in post-construction expenses such as bedroom furnishings, dining area furniture, kitchen appliances, living area furnishings, and possibly HVAC systems into your budgetary planning.
  • How can I begin my JADU development journey?
    Start by exploring guidebooks on ADU development and initiating consultations with professionals experienced in the field. They can assist in demystifying regulations and conducting a thorough analysis to help you make the right choice between a JADU and a traditional ADU.