A garage conversion is usually faster and less expensive, typically $80,000 to $150,000, because the structure already exists. A detached ADU, typically $150,000 to $300,000 or more, costs more but can be larger, sited where you want and designed from scratch. The condition of your garage and your long-term goals decide which is right.
What is the difference between a garage conversion and a detached ADU?
A garage conversion reuses an existing garage structure and turns it into a legal living unit. A detached ADU is a brand new building on its own foundation. Both end up as a complete home with a kitchen, bathroom and entrance. The difference is what you start with.
| Garage conversion | Detached ADU | |
|---|---|---|
| Typical cost | $80,000 to $150,000 | $150,000 to $300,000+ |
| Typical timeline | About 6 to 10 months | About 9 to 14 months |
| Size | Existing footprint, often 400 to 600 sq ft | Commonly up to 1,200 sq ft |
| Setbacks | Generally avoids setback issues | Typically 4 ft side and rear |
| Solar | Usually not required | Generally required |
| Design freedom | Limited by the existing shell | Fully custom |
When is a garage conversion the better choice?
A conversion makes the most sense when the garage is structurally sound, you no longer need it for parking, and your budget or timeline is tight. Detached garages at the back of the lot in older Sacramento neighborhoods like East Sacramento, Land Park and Curtis Park are often ideal, especially with alley access.
- The slab is in reasonable condition, without major cracks or settling.
- The framing and roof are sound, without significant rot or termite damage.
- There is a reasonable path for a sewer line to the main lateral.
- A studio or compact one-bedroom meets your needs.
Because conversions within the existing footprint generally avoid setback issues, they can also put a unit in a spot where a new building would not be allowed, such as right on a rear property line.
When is a detached ADU the better choice?
A new detached ADU makes sense when there is no garage, when the garage is in poor condition, or when you want more space, more privacy or a specific design. If you want two bedrooms, vaulted ceilings or a layout that opens fully to the yard, starting fresh usually costs less than forcing it into an old shell.
Detached units also tend to earn the highest rent and resale appeal, because they feel like a small house. If rental income is your main goal and the lot allows it, the higher cost is often recovered over time.
What if my garage is in bad shape?
Sometimes the right answer is to take the garage down and build new on the same spot. An old garage that needs a new slab, new framing and a new roof is no longer a conversion in any real sense. The catch is that a new building must meet current setbacks, so the replacement may need to sit a bit further from the line than the old garage did. We price both options side by side when the choice is close.
How do the costs compare per square foot?
Per square foot, the two can be closer than you would expect, because kitchens, bathrooms and utility connections are a large fixed cost in both. A conversion saves on foundation, framing and roofing. A detached ADU spreads its fixed costs over more square footage. That is why a larger detached unit can sometimes offer better value per square foot even though the total is higher.
Can I do both?
Yes, within limits. A single-family lot generally allows one ADU plus one junior ADU. An attached garage could become a junior ADU while you build a detached ADU in the backyard. Planning both at once lets us size utilities once instead of twice.
How to decide
- Have a builder inspect the garage: slab, framing, roof and sewer path.
- Decide how much space you need now and in ten years.
- Compare the full cost of each option, including utilities and solar.
- Weigh the timeline. A conversion can be months faster.
Call us and we will look at your garage and your yard together. You will get a straight answer about which path makes more sense on your lot.
Frequently asked questions
Is a garage conversion cheaper than a detached ADU?
Usually. Garage conversions typically cost $80,000 to $150,000, compared with $150,000 to $300,000 or more for a detached ADU.
Do garage conversions need solar?
Usually not. The solar requirement generally applies to new detached construction.
Can I convert a garage that is on the property line?
Generally yes. Conversions within the existing footprint generally avoid setback issues, though fire-rated construction may be needed.
Rules vary by jurisdiction and change often. Call us to confirm what applies to your property. Figures are estimates.