ADU vs. Garage Conversion: Cost, Time & Value (2026)

Q: How long does a garage conversion take versus a detached ADU?

A garage conversion typically takes 3 to 4 months to build, while a detached ADU takes 6 to 12 months depending on size and site.

Short answer: A garage conversion turns your existing garage into living space and is the cheaper, faster option — typically $100,000–$225,000 and 3–4 months to build. A detached ADU is a brand-new standalone unit that costs more ($200,000–$400,000+) and takes longer (6–12 months), but gives you more space, privacy, and rental or resale value. Choose a garage conversion to stretch your budget; choose a detached ADU to maximize space and return.

Garage conversion vs. detached ADU at a glance

Factor	Garage conversion	Detached ADU
Typical cost	$100,000–$225,000	$200,000–$400,000+
Cost per sq ft	$150–$250	$250–$400
Build time	3–4 months	6–12 months
Size	Limited to the garage footprint (+ up to 150 sq ft)	Up to 1,000 sq ft (often 1,200)
Keeps garage parking	No	Yes
Rental & resale value	Good	Higher
Best for	Budget, speed, reusing space	Space, privacy, maximum ROI

What is a garage conversion?

A garage conversion transforms your existing attached or detached garage into a legal living unit. Because the structure already exists, it is the fastest and most affordable way to add an ADU. The trade-off is that you give up garage parking and are limited to the garage footprint (California law allows up to 150 extra square feet for entry and exit).

What is a detached ADU?

A detached ADU is a brand-new standalone unit built in your yard. It costs more and takes longer, but you choose the size and layout (up to 1,000 sq ft, commonly 1,200), keep your garage, and typically gain more rental income and resale value.

Which should you choose?

Choose a garage conversion if budget and speed matter most, you can give up the garage, and the garage size fits your needs.
Choose a detached ADU if you want more space, privacy, higher rental income, and the strongest return — and you have the yard and budget for it.

Both start with a permit-ready plan set drafted to California and Los Angeles code. Jayzar offers pre-designed plans for both.

Frequently asked questions

Is a garage conversion cheaper than an ADU?

Yes. A garage conversion is usually the cheapest ADU at $100,000–$225,000, because it reuses an existing structure. A new detached ADU typically costs $200,000–$400,000 or more.

Which adds more value, a garage conversion or a detached ADU?

A detached ADU usually adds more rental income and resale value because it is larger, more private, and keeps your existing garage. A garage conversion still adds value at a lower cost.

Can I convert my garage into an ADU in California?

Yes. California law allows garage conversions into ADUs statewide, and cities cannot require you to replace the lost garage parking.

How long does a garage conversion take versus a detached ADU?

A garage conversion typically takes 3–4 months to build, while a detached ADU takes 6–12 months depending on size and site.

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ADU vs. Garage Conversion: Which Is Right for You? (2026)