If your garage is usable and your backyard is big enough, you're going to face this choice. Here's the honest framework.
Head-to-head at a glance
| | Garage conversion | Detached ADU | |---|---|---| | Typical cost (SD, 2026) | $105K–$260K | $195K–$520K | | Size | 350–600 sqft | 500–1,200 sqft | | Build time | 3–5 months | 5–8 months | | Permit time | 2–4 months | 3–6 months | | Typical rent | $1,800–$2,800 | $2,500–$4,200 | | Resale lift | 0.9×–1.1× cost | 1.2×–1.5× cost | | Privacy | Lower | Higher |
Go detached when...
- You have room for a 500+ sqft footprint plus setbacks. California state law gives you 4' setbacks on the side and rear, but you still need room for the building itself.
- You're optimizing for rent or resale. Detached ADUs consistently out-earn and out-sell converted garages.
- You want long-term tenant privacy. Separate entrance, separate exterior wall, separate roofline.
- You use your garage. If you actually store vehicles or use it as a workshop, don't convert it. Detached adds a unit without taking one away.
Go garage conversion when...
- Your budget is closer to $200K than $400K. The upfront delta is the #1 decision factor for most of our clients.
- You want it done fast. A conversion can be keys-in-hand in 6 months. A detached usually takes 12.
- Your yard is precious. Converting preserves your outdoor space.
- Your garage doesn't get used. Many San Diego garages are "storage garages" — boxes and a treadmill. That's a $200/mo rental unit waiting to happen.
- Your primary use case is in-law / adult child, not rental. The rent delta matters less when the user is family.
The often-missed hybrid option
You don't have to pick one or the other. In SD County, on a qualifying lot, you can build:
- Your primary house (existing)
- Plus one detached ADU (new build in the backyard)
- Plus one Junior ADU (a converted portion of the main house, up to 500 sqft)
That's three legal units on an R-1 lot. Many of our investor clients combine a garage conversion (serving as the JADU) with a new detached ADU to maximize door count.
The resale math
This is where most homeowners are pleasantly surprised by detached and disappointed by conversions:
Detached ADU — SD County appraisers have enough comps now to confidently value a detached ADU at 1.2×–1.5× its build cost, on top of the main house value. On a $400K build, that's $480K–$600K of added property value.
Garage conversion — Appraisers give less credit because the square footage existed before. Expect 0.9×–1.1×, which means you're often roughly even on cost-to-value. The cash flow while you hold it is still real, but the resale math is tighter.
How to decide in five minutes
Answer these three questions:
1. What's your budget ceiling? Under $260K = conversion. Over $325K = detached. In between = depends on lot. 2. Do you actually use your garage? If yes, detach. If no, either works. 3. How long will you hold the property? Under 5 years = conversion (lower upfront risk). Over 5 years = detached (better compounding).
Still stuck?
The Property Potential Report is built for exactly this decision. We'll show you both options with real numbers on your lot — cost, rent, resale, timeline — side by side.
[Get your report →](/contact)
