JADU vs Full ADU: California Rules, Costs, and Best Uses

Two Paths to Adding Housing on Your Property

California homeowners have two distinct options for creating an accessory dwelling unit: a Junior ADU (JADU) or a full ADU. Both add housing to your property, both are protected by state law, and both can generate rental income. But they differ significantly in size, cost, construction scope, and regulatory requirements.

Understanding these differences is essential before you invest time and money in a project. This guide breaks down every factor so you can make a confident decision.

Side-by-Side Comparison

Factor	JADU (Junior ADU)	Full ADU
Maximum Size	500 sqft	1,200 sqft (detached)
Location	Within existing home or attached garage	Detached, attached, or conversion
Kitchen	Efficiency kitchen allowed	Full kitchen required
Bathroom	Can share with main house	Must have its own
Cost	$40,000-$80,000	$150,000-$500,000+
Parking	None required	Generally none required
Owner-Occupancy	Required only if sharing bathroom	Not required
Permit Timeline	60 days or less	60 days or less
Separate Entrance	Required	Required
Utility Connections	Shares with main house	May require new connections
Short-Term Rental	Prohibited (30+ day minimum)	Varies by city

What Is a JADU?

A Junior Accessory Dwelling Unit is a small living space, no larger than 500 square feet, contained entirely within the walls of an existing single-family residence. JADUs were created to give homeowners the simplest, most affordable way to add a rental unit without building new structures.

Key JADU Requirements

• Size limit: 500 square feet maximum of interior livable space
• Location: Must be within a proposed or existing single-family home or attached structure such as a garage
• Kitchen: An efficiency kitchen is permitted. This means a small cooking area with a sink, counter space, and small appliances (like a microwave or hot plate). A full range or standard oven is not required.
• Bathroom: The JADU can have its own bathroom or share one with the main house
• Entrance: A separate exterior entrance is required
• Utilities: No separate utility connections needed. The JADU shares water, sewer, and power with the main house. Local agencies cannot charge connection fees for a JADU.

JADU Owner-Occupancy: The 2026 Update

One of the biggest changes for JADUs took effect on January 1, 2026, under Assembly Bill 1154. Previously, all JADUs required the property owner to live on-site (in either the main house or the JADU itself). The new rule is more flexible:

• If the JADU shares a bathroom with the primary residence, the local agency may still require owner-occupancy.
• If the JADU has its own bathroom, no owner-occupancy requirement applies.

This change makes JADUs more attractive to investors and homeowners who may want to rent out both their main home and the JADU.

What Is a Full ADU?

A full Accessory Dwelling Unit is a complete, independent living space with its own kitchen, bathroom, entrance, and often its own utility connections. Full ADUs can be built as detached structures, attached additions, or conversions of existing spaces like garages.

Key Full ADU Requirements

• Size limit: Up to 1,200 square feet for detached ADUs on single-family lots. Attached ADUs are typically limited to 50% of the primary home’s floor area or 1,200 sqft, whichever is less.
• Location: Can be detached (standalone structure), attached to the main house, or a conversion of existing space
• Kitchen: A full kitchen is required, including a sink, range or cooktop, refrigerator space, and counter area
• Bathroom: Must have its own dedicated bathroom
• Entrance: A separate exterior entrance is required
• Utilities: May require new utility connections, especially for detached units. Impact fees are waived for ADUs up to 750 sqft. For larger units, fees must be proportional to the primary dwelling.

No Owner-Occupancy for Full ADUs

California Government Code Section 66323 establishes that no owner-occupancy requirement may be imposed on full ADUs. This applies statewide. You do not need to live on the property to build, own, or rent out a full ADU.

Cost Comparison: JADU vs Full ADU

Cost is often the deciding factor between these two options. The gap is substantial.

JADU Costs

JADUs are the most affordable way to add housing in California. Because the unit is built within existing walls, you avoid the expense of a new foundation, new exterior walls, roofing, and utility trenching.

• Typical total cost: $40,000-$80,000
• Cost per sqft: $80-$160
• Major cost items: Interior framing, efficiency kitchen installation, flooring, electrical upgrades, egress window, fire separation between JADU and main house
• Average Bay Area ROI payback: Approximately 2-4 years at typical rental rates

Full ADU Costs

Full ADUs, especially detached units, involve significantly more construction.

• Typical Bay Area cost: $150,000-$500,000+
• Cost per sqft: $250-$450 (Bay Area average)
• Major cost items: Foundation, framing, roofing, full kitchen, bathroom, HVAC, utility connections, site work
• Detached ADU utility connections: Add $15,000-$30,000 for water, sewer, and electrical

The higher cost of a full ADU reflects the fact that you are building what is essentially a small, complete home.

Rental Income Potential

Both JADUs and full ADUs generate rental income, but the earning potential differs based on size, independence, and amenities.

JADU Rental Income (Bay Area)

• Studio/efficiency (400-500 sqft): $1,200-$2,000/month
• Key factor: Tenants pay less because the unit is smaller, may share a bathroom, and has an efficiency kitchen rather than a full cooking setup

Full ADU Rental Income (Bay Area)

• Studio (400-500 sqft): $2,000-$2,800/month
• One-bedroom (600-800 sqft): $2,500-$4,000/month
• Two-bedroom (900-1,200 sqft): $3,000-$4,500/month
• Key factor: Independence, full kitchen, and dedicated bathroom command higher rents

Over a 10-year period, a full ADU generating $3,000/month earns $360,000 in gross rental income compared to roughly $180,000 for a JADU at $1,500/month. The difference of $180,000 often justifies the higher construction cost.

Permit Process

Both JADUs and full ADUs benefit from California’s streamlined permitting laws. Local agencies must act on applications within 60 days. Neither type requires a public hearing or discretionary review. If the proposed unit complies with all standards, the city must approve it.

JADU Permits

JADU permits are generally simpler because the work is interior. You typically need architectural plans showing the unit layout, fire separation details, and any changes to the building envelope (such as adding an exterior entrance). No new utility connection permits are needed.

Full ADU Permits

Full ADU permits involve more documentation: site plans, structural engineering, Title 24 energy compliance, and potentially utility connection permits. Detached ADUs also require setback verification (4 feet from side and rear property lines under state law).

When a JADU Is the Right Choice

A JADU makes sense when:

• Your budget is under $100,000. JADUs deliver a functional living unit at a fraction of the cost of a full ADU.
• You have unused space inside your home. A spare bedroom wing, a large basement area, or an attached garage can be converted without expanding your home’s footprint.
• You want the fastest path to rental income. JADU projects typically take 2-4 months to complete, compared to 8-14 months for a detached ADU.
• You plan to house a family member. The proximity and shared access make JADUs ideal for aging parents or young adults who want independence but close connection.
• You want to build both. California allows one JADU and one ADU on the same lot. Starting with a JADU gets you rental income quickly while you plan a larger ADU project.

When a Full ADU Is the Right Choice

A full ADU makes sense when:

• You want maximum rental income. The larger size, full kitchen, and complete independence support significantly higher rents.
• You have adequate lot space. A detached ADU requires room on your property, but it provides the most flexibility in design and placement.
• You do not want owner-occupancy restrictions. Full ADUs have no owner-occupancy requirement, giving you complete flexibility.
• You want a two-bedroom unit. JADUs cap at 500 sqft, which limits you to a studio or small one-bedroom. A full ADU can accommodate two bedrooms and a full living area.
• Long-term property value is a priority. Full ADUs, especially detached ones, add more appraised value to your property.

Can You Build Both?

Yes. California law allows homeowners to build one JADU and one full ADU on a single-family lot. This is one of the most powerful provisions in the state’s housing law.

Here is how the combination works:

1. Convert part of your home into a JADU (up to 500 sqft, efficiency kitchen, shared or separate bathroom)
2. Build a detached full ADU in your backyard (up to 1,200 sqft with full kitchen and bathroom)

This strategy gives you two independent rental units on one property. In the Bay Area, combined rental income from a JADU ($1,500/month) and a detached ADU ($3,000/month) can reach $4,500/month or $54,000/year.

How Custom Home Approaches ADU and JADU Projects

Custom Home designs and builds both JADUs and full ADUs through our two-phase process. In Phase 1 (Design), we assess your property, evaluate which unit type fits your goals and lot, and create detailed plans with 3D visualizations. In Phase 2 (Build), we handle permitting, construction, and inspections with locked-in pricing.

For JADU projects, we focus on maximizing the livability of your existing space: smart layouts, quality finishes, and proper fire separation. For full ADUs, we design independent structures that feel like complete homes, not afterthoughts.

Whether you are building a $50,000 JADU or a $400,000 detached ADU, our process ensures you know the full scope, timeline, and cost before construction begins.

Start Your ADU or JADU Project

The right choice between a JADU and a full ADU depends on your property, budget, and goals. We can help you evaluate both options during a site assessment and recommend the approach that delivers the most value.

Schedule a free consultation to discuss your project with Custom Home.