ADU Glossary
What Is a JADU? Junior Accessory Dwelling Unit Explained
The most affordable path to adding a rental unit — built within your existing home for a fraction of the cost of a full ADU.
Quick Answer
A JADU (Junior Accessory Dwelling Unit) is a small housing unit of 500 sq ft or less created within an existing single-family home — the most affordable way to add a rental unit.
Updated April 2026
What Is a JADU (Junior Accessory Dwelling Unit)?
A JADU (Junior Accessory Dwelling Unit) is a small, self-contained living space of no more than 500 square feet created within the existing walls of a single-family home. Unlike a full ADU, which can be a separate structure, a JADU must be built within the primary residence or an attached garage — no new square footage is added to the property.
JADUs were introduced by California Assembly Bill 2406 in 2016 and further refined by AB 68 and SB 13 in 2020. They were specifically designed to be the lowest-barrier, most affordable way for homeowners to create a legal rental unit on their property.
Because JADUs are carved out of existing space, they don't require new foundations, exterior walls, or separate utility connections — all factors that dramatically reduce costs compared to building a detached or attached ADU. Typical JADU construction costs range from $50,000 to $100,000, compared to $150,000–$400,000 for a full ADU.
JADU vs ADU: Key Differences
JADUs and full ADUs serve the same basic purpose — adding a housing unit to your property — but they differ significantly in size, cost, and regulations:
| Feature | JADU | Full ADU |
|---|---|---|
| Maximum Size | 500 sq ft | 1,200 sq ft |
| Location | Within existing home | Attached or detached |
| Typical Cost | $50K–$100K | $150K–$400K |
| Separate Entrance | Required | Required |
| Kitchen | Efficiency kitchenette OK | Full kitchen required |
| Bathroom | Can share with main home | Separate required |
| Parking | None required | None required (CA) |
| Owner-Occupancy | Required | Not required (post-2020) |
| Setbacks | N/A (within home) | 4 ft rear/side (CA) |
| Impact Fees | Exempt | Exempt under 750 sq ft |
| Permit Timeline | 60 days (ministerial) | 60 days (ministerial) |
| Can Build Both? | Yes — 1 JADU + 1 ADU allowed | Yes — 1 ADU + 1 JADU allowed |
California JADU Rules & Legislation
California has the most developed JADU framework in the country. Here are the key rules as of 2026:
AB 2406 (2016) — Original JADU Law
Established the JADU concept in California, allowing cities to create JADU ordinances. Set the 500 sq ft maximum and required that JADUs be within the existing single-family home footprint.
AB 68 (2020) — Streamlined Approval
Required all cities to allow JADUs by-right (even without a local ordinance), mandated 60-day ministerial approval, and confirmed that homeowners can build both one JADU and one ADU on the same lot.
SB 13 (2020) — Fee Reduction
Eliminated development impact fees for JADUs entirely, making them even more affordable. Also reduced fees for ADUs under 750 sq ft and established a penalty process for cities that don't comply with ADU/JADU laws.
Owner-Occupancy Requirement
The property owner must live in either the primary home or the JADU. This requirement was temporarily lifted during COVID-19 but has been reinstated. This is a key difference from full ADUs, which no longer require owner-occupancy in California.
JADU Cost Breakdown
JADUs cost a fraction of a full ADU because they reuse existing structure, utilities, and often share a bathroom. Here's a typical cost breakdown:
| Cost Category | Estimated Range |
|---|---|
| Design & Architecture | $3,000–$8,000 |
| Permits & Fees | $1,500–$5,000 |
| Framing & Interior Walls | $8,000–$15,000 |
| Plumbing (kitchenette + bathroom) | $8,000–$15,000 |
| Electrical | $5,000–$10,000 |
| HVAC (mini-split) | $3,000–$6,000 |
| Kitchen/Kitchenette | $5,000–$12,000 |
| Flooring, Paint, Finishes | $5,000–$12,000 |
| Separate Entrance | $3,000–$8,000 |
| Fire Separation (if required) | $2,000–$5,000 |
| Total Estimated Cost | $50,000–$100,000 |
Advantages of Building a JADU
Pros
Lowest cost ADU option ($50K–$100K)
No setback issues — built within existing walls
No impact fees in California
Fastest permit process — no new structure review
Can share bathroom with main home
Can build a JADU and a full ADU on the same lot
Minimal disruption to yard and outdoor space
No separate utility connections needed
Cons
Limited to 500 sq ft maximum
Owner-occupancy required (you or JADU tenant)
Less privacy than detached ADU
Lower rental income than full ADU
Must be within existing home footprint
May require fire separation between units
Shared walls mean noise transfer
Efficiency kitchenette may limit appeal
JADU Utility & Kitchen Requirements
One of the key advantages of JADUs is flexibility around shared utilities. Here's what's required:
Kitchen / Kitchenette
JADUs must include a cooking facility. This can be an efficiency kitchen with a small sink, cooking appliance (hotplate, microwave, or small range), and a small refrigerator. A full-size kitchen is not required.
Bathroom
JADUs may share a bathroom with the primary residence if the JADU occupant has internal access to it. Otherwise, a dedicated bathroom is required within the JADU.
Separate Entrance
A JADU must have its own exterior entrance. This can be an existing door or a new one cut into an exterior wall.
Utilities
JADUs may share water, sewer, and electrical connections with the main home. Separate meters are not required, which significantly reduces infrastructure costs.
Compare ADU Costs for Your City
See how JADU costs compare to full ADU costs in your area.
Get Your EstimateWhen to Choose a JADU Over a Full ADU
A JADU is the right choice when:
- Your budget is under $100,000 and you want to avoid taking on significant debt
- You have unused space in your home — a large bedroom, bonus room, or attached garage
- You plan to live on the property and want to rent the other unit for supplemental income
- Your lot is too small for a detached ADU or setbacks are an issue
- You want to maximize your property's units (JADU + ADU = 3 units on one lot)
- You need a faster, simpler permit process with minimal construction disruption
- You want housing for a family member who values proximity over total independence
Frequently Asked Questions
What is the maximum size of a JADU?
A JADU (Junior Accessory Dwelling Unit) is limited to 500 square feet under California law. It must be created within the existing footprint of a single-family home or within an attached garage.
Do I need to live on the property if I build a JADU?
Yes, California requires owner-occupancy for JADUs — the property owner must live in either the primary home or the JADU. This requirement was temporarily suspended during the COVID-19 pandemic but has been reinstated.
How much does a JADU cost to build?
JADUs typically cost $50,000–$100,000 to build, making them the most affordable type of ADU. Costs are lower because JADUs are built within existing walls and can share utility connections with the main home.
Can a JADU share a bathroom with the main house?
Yes. JADUs are the only ADU type that can share a bathroom with the primary residence. However, they must have their own kitchen or efficiency kitchenette and a separate entrance.
Can I build both a JADU and a full ADU on my property?
Yes. California law allows homeowners to build both one JADU and one ADU on the same single-family lot. This means you could potentially have three units on one property — the main home, a JADU, and a detached ADU.
Does a JADU need a separate address?
Some cities require a separate address for a JADU, while others do not. Check with your local building department. A separate address can be helpful for mail delivery and emergency services.
Related Glossary Terms
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