What an ADU Is: A Quick Recap
An accessory dwelling unit (ADU) is a secondary housing unit on a residential lot — a self-contained living space with its own kitchen, bathroom, sleeping area, and entrance, built in addition to the primary dwelling. ADUs come in three physical configurations: detached (a separate free-standing structure in the backyard, sometimes called a granny flat or backyard cottage), attached (an addition to the primary dwelling that shares at least one wall), or conversion (converting existing space like a garage, basement, or attic into a habitable unit). As of 2026, ADUs are legal on residential lots in virtually all 50 states, though the specific rules about size, setbacks, permits, and fees vary dramatically. California has the nation's most comprehensive ADU laws, with a series of state statutes (AB 68, AB 881, SB 9, AB 2533) that preempt local restrictions and establish a floor of ADU rights that cities cannot reduce below. ADU development has accelerated significantly since California's 2017 reforms: the state processed over 110,000 ADU permits between 2018 and 2023, and cities like Los Angeles, San Jose, and Sacramento now process hundreds of ADU applications per month. For homeowners in California, understanding the distinction between a full ADU and a Junior ADU (JADU) is essential because the two types have very different construction requirements, size limits, and cost profiles. The right choice between them depends on your lot, your existing structures, your budget, and your housing goals.
What a JADU Is: The California-Specific ADU Subtype
A Junior ADU (JADU) is a California-specific category of secondary dwelling unit defined under California Government Code Section 65852.22. JADUs were introduced into California law in 2016 (AB 2406) and significantly expanded in 2019 and 2020. The defining characteristics of a JADU under California law are: **Size limit: Maximum 500 square feet.** This is the hard cap — a JADU cannot exceed 500 square feet of habitable floor area. This limit makes JADUs fundamentally a small-unit category, typically studio or one-bedroom configurations. **Location: Must be within the walls of an existing single-family residence or existing accessory structure.** A JADU cannot be a new free-standing structure. It must be created by converting existing space within an already-built structure. Common JADU conversions include: converting a bedroom and adjacent bathroom within the primary house into a JADU unit with its own entrance; converting an attached garage into a JADU; converting a basement that is within the walls of the existing structure. A detached garage converted to a JADU qualifies if the detached garage is designated an 'accessory structure' on the parcel. **Entrance: Must have a separate exterior entrance.** The JADU must have its own door to the outside, separate from the primary residence's main entrance. However, the JADU may also have an interior connecting door to the primary residence — this is allowed and is often convenient for multi-generational living arrangements. **Kitchen: Efficiency kitchen allowed (not full kitchen required).** A JADU may have an 'efficiency kitchen' — typically a sink, small cooktop or microwave, and counter space — rather than a full kitchen with a range. This reduced kitchen standard is one reason JADU conversions are cheaper and less complex than full ADU conversions. **Utility connections: Must share utility connections with the primary dwelling.** Unlike a full ADU (which can have separate utility connections), a JADU shares the primary dwelling's water, sewer, gas, and electrical service. This eliminates the need for separate utility meters, which can cost $10,000 to $30,000 for a full ADU depending on the city's connection fee requirements. **Owner-occupancy: Previously required; now eliminated.** California law previously required the owner to occupy either the primary dwelling or the JADU. AB 68 (2019) eliminated this requirement effective January 1, 2020 — consistent with the elimination of owner-occupancy requirements for standard ADUs.
Key Differences: ADU vs JADU Side by Side
Understanding the specific differences between ADU and JADU rules helps homeowners evaluate which option fits their situation. Here is a direct comparison: **Size limit:** - ADU: Up to 1,200 sqft for detached ADUs; attached ADUs up to 50% of primary dwelling floor area (max 1,200 sqft). Source: California Government Code Section 65852.2(c)(2)(B). - JADU: Maximum 500 sqft. Source: California Government Code Section 65852.22. **Location:** - ADU: Can be detached (new construction in backyard), attached (addition to primary dwelling), or conversion of existing space. New detached ADU construction is fully allowed. - JADU: Must be within the walls of an existing single-family residence or accessory structure. No new free-standing construction. **Kitchen requirement:** - ADU: Full kitchen required — must have a range or oven, sink, and refrigerator (full residential kitchen per building code). - JADU: Efficiency kitchen allowed — sink, small cooktop or microwave, and counter space. A full kitchen is not required. **Bathroom requirement:** - ADU: Full bathroom required — toilet, sink, and bathtub or shower. - JADU: Bathroom can be shared with the primary dwelling — a private bathroom inside the JADU is not required (though most JADU conversions include one). **Utility connections:** - ADU: Separate utility connections allowed and often required by the city. Separate electric meter, water connection, and sewer lateral may be needed. - JADU: Must share utility connections with the primary dwelling. No separate meter required. **Setbacks:** - ADU: California state law limits new detached ADU setbacks to 4 feet from side and rear property lines. - JADU: No setback requirement if created within existing structure footprint. For attached additions, primary dwelling setbacks apply. **Impact fees:** - ADU: Impact fees waived for ADUs under 750 sqft per California Government Code Section 65852.2(f)(3). Larger ADUs may face school fees. - JADU: Typically no separate utility connection fees (since connections are shared). School fees may apply for JADUs over 750 sqft, but most JADUs are under 500 sqft and are fully fee-exempt. **Applicable cities:** - ADU: All US cities (though rules vary dramatically by state) - JADU: California only — JADU is a California law concept. No other state has adopted JADU-specific legislation. Cities outside California do not recognize or permit JADUs as a distinct unit type.
Which California Cities Allow Both ADUs and JADUs?
California state law requires every city and county to allow both ADUs and JADUs on single-family lots. This means every California city that accepts building permit applications is required by law to permit both types. There are no California cities that allow ADUs but prohibit JADUs — that would violate state law. However, the local rules cities have adopted for implementing ADU and JADU approvals vary in how user-friendly and streamlined they are. Here is how the major California cities covered on PropertyZoned handle ADU and JADU permitting: **Los Angeles (ladbs.org/permits/residential/adu):** LA processes both ADU and JADU applications through the LADBS ADU Express program. Maximum JADU size: 500 sqft within existing primary dwelling or accessory structure. Maximum ADU size: 1,200 sqft detached. LA offers a library of pre-approved ADU standard plans that can significantly reduce design costs and plan check time. Total permit fees: $2,000-$8,000 for ADU; typically lower for JADU since utility connection fees are avoided. Permit timeline: 2-4 weeks for plan check via ADU Express. Source: LAMC Chapter I, Article 2, Section 12.09; California Government Code Section 65852.2. **San Francisco (sfdbi.org):** SF DBI processes both ADU and JADU applications. Maximum JADU size: 500 sqft within existing structure. Maximum ADU size: 1,200 sqft detached (new) or conversion of existing accessory structure. Total permit fees: $3,000-$10,000 for ADU; JADU fees typically lower. The SF Planning Department pre-approval process may add time for projects in historic districts or that require design review. Source: SF Planning Code Section 207.1; California Government Code Section 65852.22. **San Jose (sanjoseca.gov/adu):** San Jose PBCE processes both types. JADU: 500 sqft maximum within existing structure or garage. ADU: 1,200 sqft maximum detached. Total fees: $2,500-$8,500. Silicon Valley's high land costs and housing demand make both ADU and JADU development economically attractive — a garage conversion JADU in San Jose can rent for $1,500-$2,500 per month depending on location. Source: San Jose Municipal Code Title 20; California Government Code Section 65852.22. **Sacramento (cityofsacramento.gov/adu):** Sacramento CDD processes both types. JADU: 500 sqft maximum within existing structure. ADU: 1,200 sqft maximum detached. Total fees: $2,000-$7,500 for ADU; typically lower for JADU. Sacramento's older housing stock (many 1940s-1970s homes) often has detached garages that qualify as accessory structures for JADU conversion. Source: Sacramento City Code Title 17; California Government Code Section 65852.22. **San Diego:** San Diego Development Services Department processes both types per state law. San Diego has pre-approved standard ADU plans and offers JADU conversion assistance for homeowners. The city's mild climate makes outdoor-to-indoor ADU and JADU conversions particularly viable.
Cost Comparison: ADU vs JADU
The cost difference between building a full ADU and converting space to a JADU is significant and is one of the most important factors in the decision between the two. **JADU conversion costs** are lower because: 1. No new construction is required — you are converting existing space that already has a foundation, walls, and roof. 2. No separate utility connections are needed — the shared connection requirement eliminates connection fees ($10,000-$30,000 for separate water, sewer, and electrical meters in many California cities). 3. The smaller size (max 500 sqft) reduces the scope of work even for JADU conversions that require significant interior reconstruction. 4. Building code requirements are somewhat reduced (efficiency kitchen rather than full kitchen; shared bathroom allowed in theory). For a typical garage conversion to JADU in Los Angeles or San Jose, total project costs (design, permits, construction) typically run $50,000 to $120,000. Simpler bedroom-suite conversions within the primary dwelling can be done for $30,000 to $80,000. **ADU construction costs** are higher because: 1. New detached ADU construction requires a full foundation, framing, roofing, and all building systems. 2. Separate utility connections (water, sewer, electrical) may add $10,000 to $30,000 beyond the permit fees. 3. The larger maximum size (up to 1,200 sqft for detached) enables more expensive projects. 4. San Francisco and Los Angeles construction labor rates are among the highest in the US. For a new detached ADU in Los Angeles, total project costs typically range from $150,000 to $350,000 depending on size, finishes, and site complexity. In San Francisco, costs run $200,000 to $500,000 for a new detached ADU. Pre-fabricated ADU units have emerged as a cost-reduction option — some manufactured ADU suppliers offer complete units installed for $100,000 to $200,000. **When to choose JADU:** If your property has an existing attached or detached garage, basement, or large room that can be isolated with a separate entrance, a JADU conversion is almost always cheaper than new ADU construction. It is the right choice when budget is primary, when you want a smaller unit for multi-generational living or modest rental income, or when your lot's setbacks or size prevent a full detached ADU. **When to choose ADU:** If you have the budget for new construction and want a larger, more valuable unit (800-1,200 sqft detached ADUs command significantly more rent than 400-500 sqft JADUs), or if your property has no convertible existing structures, a full ADU is the better long-term investment.
Permit Differences: ADU vs JADU
The permitting process for ADUs and JADUs is similar at the macro level — both require building permits in California — but there are meaningful differences in specific steps and required documentation. **ADU permit process:** 1. Verify feasibility: Confirm your lot and zone support an ADU with the required setbacks and lot coverage remaining. 2. Hire an architect or use pre-approved plans: Most cities require stamped architectural plans. LA, San Diego, and some other cities offer pre-approved standard plan sets that can reduce design costs and plan check time significantly. 3. Submit for permit: Submit to the city building department. In California, cities must process ADU/JADU applications ministerially within 60 days (California Government Code Section 65852.2(a)(3)). 4. Utility coordination: If your ADU will have separate utilities, coordinate with your utility providers for connection points and fees before construction. 5. Construction with required inspections: Foundation, framing, rough electrical, rough plumbing, insulation, and final inspections. 6. Certificate of Occupancy: Required before occupancy. **JADU permit process:** 1. Verify the space qualifies: Confirm that the space to be converted is within an existing single-family residence or accessory structure. 2. Prepare plans: Plans must show the proposed JADU configuration, the separate entrance, utility sharing arrangement, and code-compliant habitability improvements. 3. Submit for permit: Same 60-day ministerial approval requirement as ADU. 4. No separate utility connection coordination: Since utilities are shared, no separate connection applications are needed. 5. Construction with inspections: Structural, electrical (if being upgraded), egress (window sizing), insulation, and final inspections. 6. Certificate of Occupancy or Letter of Completion: Required before occupancy. JADU permits typically have a faster timeline and lower total cost than full ADU permits — the plan check is less complex because there is no new structure, no foundation work, and no separate utility connections. In LA's LADBS ADU Express program, JADU permits are often processed faster than new detached ADU permits.
JADUs Outside California: What Other States Offer
JADU as a legal concept exists only in California — no other state has adopted JADU-specific legislation. However, the underlying idea of a small, internally-converted secondary unit within an existing residence is not unique to California and is enabled by ADU rules in many other states under different names. In Oregon, which has strong statewide ADU law through HB 2001 (2019), ADUs can be created within existing structures without a specific JADU designation. Portland's ADU rules allow 'interior ADUs' — units created within the existing footprint of the primary dwelling — that function similarly to California JADUs. No separate JADU category is defined in Oregon law, but the effect is similar. In Washington State, where HB 1337 (2023) created statewide ADU rights, attached ADUs and internal conversions are permitted without a JADU-specific category. Seattle's ADU rules allow both attached and internal ADUs created within the existing dwelling, subject to city-specific size and design standards. In states without statewide ADU laws (Texas, Illinois, New York, Florida prior to 2024), the availability of internally-converted secondary units varies entirely by city code. Austin's Development Code allows secondary apartments (ADUs) in various configurations but does not distinguish between internal conversions and new construction in the same way California's JADU designation does. For homeowners outside California who want a small, low-cost secondary unit created by converting existing space, the answer is to check your city's ADU or accessory dwelling unit rules. If internal conversions are permitted (which they typically are in cities with any ADU allowances), you can create the functional equivalent of a JADU — just without the specific California label and its associated regulatory framework. For homeowners in California, the JADU designation is a valuable tool that reduces costs and complexity compared to full ADU permitting. If you have a detached garage, attached garage, basement, or large room that can be converted, investigating the JADU pathway with your city's building department is worth the time — it may cost significantly less than building a new detached ADU while still generating meaningful rental income.
Frequently Asked Questions
What is a JADU?
A Junior ADU (JADU) is a California-specific secondary dwelling unit of no more than 500 square feet, created within the walls of an existing single-family residence or existing accessory structure (like a garage or basement). JADUs are defined in California Government Code Section 65852.22. Key features: must have a separate exterior entrance, must share utility connections with the primary dwelling, allows an efficiency kitchen rather than a full kitchen, and requires the same ministerial permit approval within 60 days as a standard ADU. JADUs are only recognized in California — no other state has equivalent legislation.
Can I build a JADU outside California?
No — JADU is a California-specific legal concept defined in California Government Code Section 65852.22. No other state has adopted JADU legislation. Outside California, you can still create a small secondary unit within an existing structure (which functions like a JADU) under whatever ADU or accessory dwelling rules your city allows, but it would not be called a JADU and would not benefit from California's specific JADU protections (ministerial approval, no separate utility connection fees, etc.).
How big can a JADU be?
A JADU cannot exceed 500 square feet under California Government Code Section 65852.22. This is a hard cap in state law that no city can exceed. Most JADUs are studio or one-bedroom configurations in the 300-500 sqft range. In comparison, a full detached ADU can be up to 1,200 sqft under state law. The 500 sqft limit makes JADUs best suited for modest studio or one-bedroom rentals or multi-generational living where a small private space is sufficient.
Does a JADU require a separate bathroom?
No — California law does not require a JADU to have a private bathroom. The bathroom can be shared with the primary dwelling, accessed through the internal connecting door that JADUs are allowed to have between the unit and the main house. In practice, most JADU conversions include a private bathroom within the unit because tenants expect private facilities, but the legal requirement does not mandate one. This flexibility is one reason JADU conversions of existing bedrooms with shared bathrooms can be relatively inexpensive.
Is a JADU cheaper to build than a full ADU?
Generally yes — significantly cheaper. A JADU conversion of an existing attached garage or large room in Los Angeles typically costs $50,000 to $120,000 total (design, permits, construction), while a new detached ADU in the same city costs $150,000 to $350,000 or more. The cost advantage comes from: no new structure to build (foundation, framing, roofing), no separate utility connection fees ($10,000-$30,000 savings), and a smaller overall scope of work. The tradeoff is that the JADU is smaller (max 500 sqft) and must be within an existing structure.