Accessory Dwelling Units (ADUs) and Junior ADUs (JADUs): Understanding the Core Concept
An Accessory Dwelling Unit (ADU) is a secondary, independent living unit inside a primary home or in a detached structure on the same property. A Junior Accessory Dwelling Unit (JADU or JrADU) is the same thing with lower kitchen and bath requirements, a minimum size of 150-220sf and a maximum size of 500sf, and they must be fully contained in the primary home on the property (JrADU's can not be permitted in detached structures at this time).
Both the ADU and JADU monikers fundamentally refer to a permitted use designation for a property, obtained through a building permit process.
The ADU or JADU permitted use designation is what truly matters: it legally allows more than one independent living space (and crucially, more than one kitchen) on a single-taxed lot that would otherwise be restricted to a single-family home with one kitchen. Most people think of an ADU as a separate "granny flat" or backyard cottage—and that fits if permitted property —but the physical work (whether converting existing space inside the home, renovating a detached structure like a pool house, or building something new that adds to internal space of a property or creates a detached structure ) is secondary. The primary value lies in changing the property's permitted use from "single kitchen/single family" to "multiple kitchens/multiple living units," all while keeping it under one ownership, one tax parcel, and one set of utilities in most cases.
Why does this ADU or JADU distinction matter? The number of kitchens is the key trigger that appraisers, banks, insurers, and tax authorities use to categorize a property. A second kitchen signals potential for separate living—reclassifying it as a "property with ADU" (higher value, different lending rules) rather than a plain single-family home, or distinguishing it from a true duplex (which often implies separate utilities/meters and sometimes separate ownership). Banks rely on this permitted use designation for loan eligibility and rates; appraisers use it for valuation; insurers adjust policies accordingly.
Experienced real estate professionals, tax authorities, and lenders may not immediately assume that obtaining an ADU or JADU permitted use opens a straightforward path to condominium conversion (splitting the property into separately sellable units on the same lot). Condominium conversions are more commonly associated with traditional duplexes, triplexes, or larger buildings that already have separate metering and clear unit boundaries. Performing a conversion on ADU/JADU units—especially internal ones that share utilities—introduces significant administrative complexities for permitting, tax rolls, utility billing, HOA formation (if needed), and resale processes.
Although California recently enacted laws allowing such conversions in some cases, this appears to have caught many local permitting agencies off-guard, creating confusion at the counter level. Rather than embracing the full potential, some municipalities may inadvertently (or deliberately) downplay internal ADU/JADU options to avoid future headaches.
For homeowners, the real, immediate benefit lies in mastering the permitted use designation itself—unlocking rental income, multigenerational living, or increased property value—without pursuing the far more complicated condominium step -- which allows separate sales of parts of a parcel, but gets complex and unwieldy quickly.
In short, ADUs and JADUs aren't just about building something extra—they're a zoning and permitting tool that unlocks density, rental income, multigenerational living, or resale value on existing lots, with the kitchen count serving as the practical gateway. Understanding this reveals why internal units (essentially creating a permitted "duplex-lite" under one roof and one tax bill) or a detached unit (essentially creating two homes on one one tax bill) are often the easiest, lowest-impact path to adding housing density -- yet the internal unit options remain the least highlighted on county resources, possibly due to the downstream complexities they can introduce for local agencies IF people then want to pursue condo conversions.
Clarifying ADU/JADU Locations: Internal, Attached, and Detached
To avoid confusion during planning or permitting (especially when combining remodels with ADU/JADU creation), here's how the two main location types break down and a word that may sound good but should not be used.
Internal: The unit is created entirely within the existing walls of the primary home (e.g., converting a bedroom suite, basement, attic, or portion of the main floor). No footprint expansion; shares walls, roof, and utilities seamlessly. JADUs must be internal; full ADUs can be too (up to state size limits).
Attached: The unit is added onto the primary home (e.g., bump-out, over-garage addition, or enclosed breezeway connection). It becomes part of the main structure's envelope—still "under one roof" with integrated utilities. Think about adding space to the home first to create more space and then using that internal space to for and ADU. (Thus the term 'attached' should NOT be used in the permitting process to avoid confusion unless all parties are clear it's a space addition and conversion).
Detached: A completely separate structure on the lot (e.g., new backyard cottage or converted pool house/garage not connected to the home). Requires its own foundation, roof, and often more utility routing. This is the type most heavily featured on county websites, despite often being the most complex and impactful option.
Internal ADU's and JADUS typically involve the least review/friction (ministerial, shared systems), making them ideal for quick density gains—yet they're the least explained locally with reasons unclear.