What Is the Difference Between an ADU and JADU in California?

California’s housing market presents significant challenges for residents, with high costs and limited availability in many areas. 

As the state addresses these issues, creative solutions have emerged to increase housing density and affordability. Two notable options are Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs). 

While both provide potential answers to housing needs, they have distinct characteristics and regulations. This guide explores the critical differences between ADUs and JADUs in California, helping homeowners understand their options.

ADUs (Accessory Dwelling Units)

Accessory Dwelling Units, commonly known as ADUs, have become popular as a flexible housing solution. But what exactly are they?

An ADU is a secondary housing unit on a single-family residential lot. It’s a self-contained living space with a kitchen, bathroom, and sleeping area. ADUs can be used for various purposes, from housing family members to generating rental income.

ADUs come in several forms:

  1. Detached ADUs: Standalone structures separate from the main house
  2. Attached are ADUs: Units connected to the primary residence
  3. Converted ADUs: Existing spaces (like garages or basements) transformed into living areas

In California, ADUs are subject to specific size restrictions. Detached ADUs can be up to 1,200 square feet, while attached ADUs can be up to 50% of the primary dwelling’s living area, not exceeding 1,200 square feet.

ADUs serve multiple purposes and offer various benefits. They provide additional housing for family members or renters, increase property value, and generate rental income.


JADUs (Junior Accessory Dwelling Units)

Junior Accessory Dwelling Units, or JADUs, are a newer concept in California’s housing landscape. 

A JADU is a small living unit created within the walls of an existing single-family home. Unlike ADUs, JADUs are always part of the main house structure.

JADUs have distinct features that set them apart:

  • Always located within the main house
  • Typically converted from an existing bedroom
  • May share a bathroom with the main house
  • Require an efficient kitchen

JADUs have stricter size limitations than ADUs. They can be no larger than 500 square feet and must be contained entirely within an existing single-family residence.

JADUs offer unique advantages. They provide an affordable housing option with minimal construction and allow homeowners to age in place by renting out the main house.

JADUs also provide a private living space for adult children or caregivers, increasing housing density without changing the neighbourhood’s character.

Critical Differences Between ADUs and JADUs

Understanding the distinctions between ADUs and JADUs is crucial for homeowners considering these options. Let’s break down the key differences:

Size comparison:

  • ADUs: Up to 1,200 square feet
  • JADUs: Maximum 500 square feet


Location within the property:

  • ADUs: Can be detached, attached, or converted from existing spaces
  • JADUs: Must be within the walls of the existing single-family home

Kitchen facilities:

  • ADUs: Require a full kitchen
  • JADUs: Only need an efficiency kitchen (sink, cooking appliance, food prep counter, storage cabinets)

Bathroom requirements:

  • ADUs: Must have their bathroom
  • JADUs: Can share a bathroom with the main house

Separate entrance requirements:

  • ADUs: Must have a separate exterior entrance
  • JADUs: Require a separate entrance, but it can be shared with the main house

Owner-occupancy rules:

  • ADUs: As of 2020, California doesn’t require owner occupancy for ADUs built between January 1, 2020, and January 1, 2025
  • JADUs: The property owner must live in either the primary residence or the JADU


Parking requirements:

  • ADUs: Generally, no additional parking is required if the ADU is within 1/2 mile of public transit
  • JADUs: No additional parking is required

Legal and Zoning Considerations in California

California has enacted several laws to improve the process of building ADUs and JADUs. These include AB 68, AB 881, and SB 13 (2019), which reduced barriers to ADU construction. AB 670 (2019) prohibits homeowners associations from unreasonably restricting ADUs, while AB 3182 (2020) further eased restrictions on ADUs and JADUs.

Zoning restrictions have been adjusted to encourage ADU and JADU construction. However, local jurisdictions may have specific requirements, so it’s essential to check with your local planning department.

The permitting process for ADUs and JADUs can differ. ADUs often require more extensive permitting due to their larger size and potential for being detached structures. JADUs, on the other hand, typically have a more straightforward permitting process as they’re contained within the existing home.

Pros and Cons of ADUs vs. JADUs

When deciding between an ADU and a JADU, consider these advantages and potential drawbacks:

ADU advantages:

  • Larger living space
  • More flexibility in design and location
  • Potential for higher rental income

ADU drawbacks:

  • Higher construction costs
  • It may require more extensive permitting
  • Could impact outdoor space

JADU advantages:

  • Lower construction costs
  • Simpler permitting process
  • Maintains existing home layout


JADU drawbacks:

  • Limited size
  • Less privacy due to being within the main house
  • Restricted to existing home footprint

The best option depends on your needs, budget, and property characteristics. 

ADUs might be preferable for those seeking a larger, more independent living space. At the same time, JADUs could be ideal for homeowners wanting to make the most of existing space with minimal construction.


Understanding the differences between ADUs and JADUs is essential for California homeowners considering these housing options. Both offer unique benefits and can help address the state’s housing challenges in their ways. 

Whether you’re looking to provide housing for family members, generate rental income, or increase your property’s value, ADUs and JADUs present viable solutions. As regulations evolve, staying informed and consulting with local authorities or housing experts is crucial to make the best decision for your property and needs.

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