What Is a Junior ADU?

A Junior ADU, also known as a JADU, is a small residential unit created entirely within the walls of an existing single-family home. Unlike a traditional ADU, a Junior ADU does not involve expanding the building footprint and is designed to make use of existing interior space in a more efficient way.

Junior ADUs are primarily intended to increase housing flexibility while maintaining neighborhood character and minimizing new construction.

How It Works

A Junior ADU is formed by converting part of an existing home — such as a large bedroom or a portion of the floor plan — into a separate living space.

To qualify as a Junior ADU, it must include:

• A separate entrance from the main home
• An efficiency kitchen space
• Up to 500 square feet of living area
• Connection to the main home’s utilities

Unlike a standard ADU, a Junior ADU usually shares bathrooms and some utilities with the primary residence.

Junior ADU vs Standard ADU

While both provide additional housing options, Junior ADUs and traditional ADUs differ in several important ways.

A Junior ADU:

• Must be entirely within the existing home
• Has a maximum size of 500 square feet
• Shares sanitation facilities with the main dwelling (if allowed by local code)
• Typically requires less construction work

A traditional ADU:

• Can be detached or attached
• Can be much larger
• Must include its own bathroom
• Often requires new structural elements

Why Homeowners Build Junior ADUs

Many homeowners create Junior ADUs to generate rental income, accommodate extended family, or add more functionality to underutilized interior space.

They are also popular because they typically require:

• Lower construction costs
• Faster approval processes
• Less disruption than full ADU builds

Junior ADUs are often used for aging parents, students, or long-term rental opportunities.

Permitting and Code Considerations

Even though a Junior ADU often requires less construction, it still needs proper permits and compliance approval.

Most Junior ADU projects must meet local planning requirements as well as Title 24 energy compliance when changes affect energy systems such as insulation, ventilation, or heating and cooling components.

A professional compliance consultant can help determine whether your project requires a Title 24 report.

What You Need to Build a Junior ADU

To start a project, you will typically need:

• Architectural plans showing the conversion layout
• Floor plan measurements
• Existing and proposed electrical layouts
• Door and kitchen configuration details
• Local zoning review

These documents help your city determine whether your Junior ADU meets legal requirements.

How to Get Guidance on a Junior ADU Project

If you’re planning a Junior ADU, it’s important to understand how it impacts your building compliance, permits, and energy documentation.

Call (626) 365-1518 or submit your details through our online contact form and our team will guide you through the process.

Final Thoughts

It’s a smart way to convert part of your existing home into a functional independent living space, offering flexibility, income potential, and efficient use of square footage.

For professional guidance on required compliance and documentation, call (626) 365-1518 today.