“ADU” is an umbrella term that covers four legally distinct types of construction, and the type you choose determines your budget, timeline, and how independent the finished space feels. Apex Homes builds one of them, the detached ADU, and handles the process from design through permitting and construction.
The 4 Types of ADUs
Detached ADU
A detached ADU is a fully standalone structure built elsewhere on the same lot as the main house. It has its own foundation, roofline, kitchen, bathroom, and entrance, which makes it the most private and independent of the four types. Because it’s new construction rather than a conversion, a detached ADU typically costs $205,000 to $438,000 or more, depending on size and site conditions. This is the type Apex Homes specializes in. Browse pre-approved detached ADU floor plans, including a 1-bedroom design starting around $205,000.
Attached ADU
An attached ADU shares at least one wall with the main house, often created through a home addition or a larger interior reconfiguration. Because it can share some existing utilities and structure, it’s generally less expensive than detached construction, typically $100,000 to $250,000 or more.
Garage Conversion ADU
A garage conversion ADU reuses an existing garage’s foundation, walls, and roofline, adding a kitchen, bathroom, and separate entrance to turn it into a self-contained unit. Since it starts with an existing structure, it’s usually the most budget-friendly option that still counts as a full ADU, typically $100,000 to $180,000.
JADU
A Junior Accessory Dwelling Unit (JADU) is smaller and more restricted than any ADU type. California law caps a JADU at 500 square feet, and it must be built entirely within an existing single-family home’s footprint, most often a converted bedroom. For a full breakdown of how a JADU compares to a full ADU.
Types at a Glance
| Type | Location | Max Size | Kitchen | Typical Cost |
|---|---|---|---|---|
| Detached ADU | Standalone structure on the same lot | Up to 1,200 sq ft | Full kitchen required | $205,000–$438,000+ |
| Attached ADU | Shares a wall with the main house | Varies by jurisdiction | Full kitchen required | $100,000–$250,000+ |
| Garage Conversion | Existing garage footprint | Varies by garage size | Full kitchen required | $100,000–$180,000 |
| JADU | Inside existing home footprint | 500 sq ft | Efficiency kitchen allowed | $40,000–$100,000 |
Apex Homes builds detached ADUs specifically. Attached ADUs, garage conversions, and JADUs are typically better suited to a general contractor.
Which Type Fits Your Property?
A few factors can help narrow down the right type for your lot.
- Budget: JADUs and garage conversions cost less since they reuse existing structure, while detached and attached ADUs involve more new construction.
- Existing structure: if you have an underused garage, a garage conversion is often the fastest path to added space.
- Lot size: detached ADUs need enough yard space for a standalone structure, while JADUs and garage conversions work on tighter lots.
- Rental income goals: detached ADUs typically command the highest rent and read as the most independent to renters and appraisers.
If a detached ADU looks like the right fit, a free estimate from Apex Homes can walk through your property’s zoning, square footage, and budget, and our ROI Calculator can show what kind of return it might generate over time.
Detached ADU Construction in the Bay Area with Apex Homes
Apex Homes designs, permits, and builds detached ADUs throughout the Bay Area, handling the process from initial planning through final construction. Learn more about how our process works, browse pre-approved ADU floor plans, or request a free estimate for a cost breakdown specific to your address.