Detached, Attached, and Conversion ADUs, Plus the JADU
Detached, attached, conversion, or JADU? Here is a plain-English guide to the main ADU types for Downey homeowners, and how to figure out which one fits your lot.
Why we start with the type of ADU
When most people picture an ADU, they see a small detached cottage in the backyard. It is one type, not the only one, and the type you pick determines the cost, the timeline, the permitting, and how the unit works on your property. Settling on the right type for your lot and your goals is the first real decision in any ADU project.
California law recognizes several distinct categories of accessory dwelling unit, and each has its own rules and trade-offs. Understanding them up front helps you have a productive conversation about what is possible on your Downey lot, rather than fixating on one image of what an ADU has to be.
We design and build all of these types ourselves, so we have no incentive to steer you toward a single choice. What follows is the straight version of how they stack up.
Detached ADUs
A detached ADU is a standalone unit, separate from the main house, usually placed in the backyard or to the side. It is the most private and flexible option, since it functions as its own small home with its own entrance, and it tends to add the most value and rental appeal because of that independence.
The trade-off is that a detached unit is new construction from the ground up: its own foundation, full framing, a roof, and new utility connections. That makes it generally the most involved and the most expensive type, and it needs enough lot area and the right access to build. The deeper rear yards common on Downey-area tract lots are often a good fit.
If you have the space and the budget, a detached ADU tends to be the most satisfying option, mainly because it is a real, independent dwelling and not a piece carved out of the existing house.
- Standalone unit, separate door, real privacy
- Great versatility with strong rental potential
- New foundation, framing, roof, and service lines
- Needs adequate lot area and access to the rear
- Generally the largest project of the three
Conversions and attached ADUs
An attached ADU connects to the existing home by at least one wall and is built as an extension of the main structure. It tends to be less expensive than a fully detached build since it relies partly on the existing foundation and structure, yet still delivers a separate living space with its own way in.
A conversion ADU reuses existing space, most commonly a garage, but sometimes another underused part of the home. Because the shell already exists, a conversion can be one of the more affordable paths to an ADU, and garage conversions are especially common in this part of the county. The real cost depends on the condition of what you are converting and what it takes to make it a code-compliant dwelling with proper insulation, systems, and egress.
If a detached build does not match the lot or the budget, attached units and conversions are both good options. The right one depends on your existing structure, your space, and what you want the unit to accomplish.
Inside the Junior ADU (JADU)
A junior accessory dwelling unit, or JADU, is a smaller kind of unit built within the existing single-family home, typically by converting a bedroom or similar space. JADUs are held to a smaller size than a standard ADU and carry their own rules, such as an efficiency kitchen and, in many cases, an owner-occupancy mandate.
What makes a JADU appealing is its affordability and simplicity. Because it is carved out of existing conditioned space, it can be among the least costly ways to add a small, legal rental or family unit, and current rules sometimes allow it together with a separate ADU on the same lot.
What limits a JADU is size and configuration, since it is small by design and belongs to the main home rather than standing separately. For the right homeowner, though, it is an affordable way to add a compact, income-capable or family unit.
Lining up the type with your lot
The right type depends on a few questions worth asking. How much lot area and access do you have to work with? What is your budget? Would you rather a fully independent unit or a smaller space carved from the home? And what is the purpose: housing family, generating rent, or providing flexible space for the future?
We walk your property and talk through all of it, then recommend the type or types that genuinely fit. A deeper lot with good rear access and a real budget may point to a detached unit; a tighter lot or a tighter budget may point to a garage conversion or a JADU. There is no universally correct type, only the right one for your situation.
Starting the design with the actual constraints of your lot is how we keep the build doable and the budget honest, regardless of which type you go with.
Questions homeowners have about ADU types
We are often asked whether a homeowner can build more than one ADU. Current California rules permit many single-family lots to add both a standard ADU and a JADU, though the details depend on the lot and the local code, which we confirm for your property. As for whether a conversion or a detached unit is the better rental, a detached unit typically commands higher rent for its privacy, while a conversion can be the smarter play on cost.
Another question that arises is whether type bears on the schedule. It does, because a conversion of sound existing space tends to be faster than ground-up detached construction, with much of the structure in place. We provide a realistic timeline for your specific type when we consult.
During a free consultation we sort all of these out for your lot, since the right type is the one suited to your property and your objectives, not a one-size recommendation.
How the type shapes the whole project
The type you choose does more than set the price. It shapes the timeline, the permitting path, the disruption to your daily life, and the value the finished unit adds to the property. A detached new build is the longest and most involved process but delivers the most independent dwelling; a conversion is faster and less disruptive but limited to the structure you start with; a JADU is the simplest of all but the smallest.
It also shapes how the unit lives once it is done. A detached unit gives a tenant or a family member real separation and privacy, which is part of why it commands more as a rental. A conversion or a JADU keeps everyone closer to the main house, which can be exactly what a multigenerational household wants, or exactly what it does not, depending on the family.
There is no single best type, only the type that fits your lot, your budget, your timeline, and what you need the unit to do. Walking through those four questions honestly, before any drawing happens, is how we make sure the project starts on the right foot rather than fixating on the picture of a backyard cottage that may or may not suit your situation.
Detached, attached, conversion, or JADU, no single type is right for everyone, and the best option depends on your property, your budget, and what you expect the unit to accomplish.
If you are weighing the options in Downey, call 951-579-3268 for a free design consultation and an honest read on what fits your property.
Reach our Downey crew at 951-579-3268 for a design visit and estimate.