Ventura County
Junior ADU (JADU) Design and Construction
A smaller unit created entirely inside an existing single-family home, with its own California requirements.
What a JADU is
A Junior Accessory Dwelling Unit is a distinct category under California law. The defining features are that it is no more than 500 square feet and that it is created entirely within the walls of an existing or proposed single-family dwelling.
A JADU must include an efficiency kitchen. It may share a bathroom with the main house, or it may have its own. It needs its own exterior entrance, and it may also retain an interior connection to the house.
How a JADU differs from an ADU
| ADU | JADU | |
|---|---|---|
| Maximum size | Commonly up to 1,200 sq ft depending on type and jurisdiction | 500 sq ft |
| Location | Detached, attached, or converted from an existing structure | Entirely within an existing or proposed single-family home |
| Kitchen | Full kitchen | Efficiency kitchen |
| Bathroom | Its own | Its own, or shared with the main house |
| Separate entrance | Required | Required |
| Impact fee threshold | Generally exempt at 750 sq ft of interior livable space or less | Generally exempt at 500 sq ft or less |
Owner occupancy, and what changed for 2026
Owner occupancy has historically been the significant catch with Junior ADUs. California law has generally required the property owner to live in either the main house or the JADU, recorded against the property.
That has changed for some situations. Under AB 1154, effective January 1, 2026, the owner-occupancy requirement is eliminated where the JADU has its own bathroom rather than sharing one with the primary dwelling.
This is exactly the kind of rule that changes, and the details matter for your specific property. Confirm the current requirement with your jurisdiction, or ask us to confirm it for your address, before you make a financial decision based on it.
When a JADU makes sense
- The house has an underused bedroom, a converted den or a section that can be separated cleanly.
- You want the smallest, least disruptive route to a legal second unit.
- The lot has no room for a detached unit and no garage worth converting.
- You want to combine it with an ADU. Many single-family properties can have one ADU and one JADU, which is a route worth asking about.
What it takes to build one
Less demolition than most people expect and more code work than most people expect. The efficiency kitchen, the separate exterior entrance, the fire separation between the unit and the rest of the house, the electrical and the egress all have to be right. It is a small project with a full-size permit set.
Before you plan one
Junior ADU Questions
What is the difference between an ADU and a JADU?
A JADU is capped at 500 square feet and must be created entirely within an existing or proposed single-family home, with an efficiency kitchen and possibly a shared bathroom. An ADU can be detached, attached or converted, is commonly allowed up to 1,200 square feet depending on type and jurisdiction, and needs its own full kitchen and bathroom.
Do I have to live on the property if I build a JADU?
California law has generally required owner occupancy for JADUs. Under AB 1154, effective January 1, 2026, that requirement is eliminated where the JADU has its own bathroom rather than sharing with the primary dwelling. Rules in this area change, so confirm the current requirement for your property before relying on it.
Can I have both an ADU and a JADU?
Many single-family properties in California can have one ADU and one JADU. Whether yours can depends on your jurisdiction and your parcel.
Does a JADU need its own kitchen?
It needs an efficiency kitchen, which has a narrower definition than a full kitchen. We design it to whatever your jurisdiction requires.
Junior ADUs
The smallest route to a legal second unit.
If there is unused space inside the house, a JADU may be worth looking at before anything else.