Two of the most common ADU paths in the Sacramento region are the ground-up detached ADU and the garage conversion. Both create a legal second unit, but they differ significantly in cost, timeline, and design flexibility.
Cost
Garage conversions typically run $25,000–$150,000, while detached ADUs typically run $105,000–$300,000. The gap comes down to starting conditions: a garage conversion reuses an existing foundation, roof structure, and often partial utility infrastructure, while a detached ADU is built entirely from scratch.
Timeline
Garage conversions are generally faster to permit and build since less new structure is involved. Detached ADUs require full foundation work, framing, and roofing, which extends both the construction timeline and the engineering and permitting phase.
Design Flexibility
A detached ADU gives you a blank slate — you can size and orient the unit for maximum rental appeal or personal use. A garage conversion is constrained by the existing garage footprint and location on the lot, though that constraint is often exactly why it's more cost-efficient.
Which Should You Choose?
If your goal is the fastest, most cost-efficient path to rental income and you have a usable garage, a conversion is usually the stronger investment case. If you have backyard space and want maximum design control — or your garage is needed for parking or storage — a detached ADU is the better fit. We walk every client through this decision during the feasibility phase of our ADU construction process.