Garage Conversion vs. Detached ADU. What’s the Difference?

Accessory Dwelling Units (ADUs) have become one of the most practical ways to add value, create flexible space, and generate long-term rental income on residential properties in Los Angeles. With updated state laws and streamlined city processes, it’s now easier than ever for homeowners to pursue ADU development. One of the first major decisions to make is whether to convert an existing garage or build a new detached unit from the ground up. While cost is often the first consideration, the two options differ in more than just price, they vary in permitting timelines, construction scope, long-term use, and what’s actually allowed under local zoning.

This guide breaks down both approaches using current Los Angeles regulations, market rental data, and construction trends to help you understand which path may work best for your property.

Section 1: Cost Comparison – What You’ll Spend and Why

Garage Conversions

Garage conversions typically cost between $95,000 and $135,000 in Los Angeles. This makes them the most accessible option for many homeowners. Using the existing foundation, framing, and rough utilities can reduce material and labor costs.

However, many LA garages were built decades ago and do not meet modern structural or energy code. Common issues include cracked or unreinforced slabs, outdated wiring, uninsulated walls, and ceilings under the required 7 feet. These conditions often require upgrades that can increase total cost and extend the construction timeline.

The California Department of Housing and Community Development (HCD) confirms that replacement parking is not required for garage conversions in most transit-adjacent zones. But that does not eliminate the need for structural compliance. Always verify garage condition with a licensed general contractor or structural engineer before finalizing a budget.

Detached ADUs

Detached ADUs require a full construction scope: new foundation, utilities, framing, and finish. In Los Angeles, costs typically range from $180,000 to over $300,000, depending on size, access, finish level, and site conditions. Projects on hillside lots or narrow parcels may require grading, retaining walls, or specialized structural solutions.

The California Residential Cost Guide and local contractor pricing show that most detached ADUs fall between $300 and $400 per square foot. While more expensive, detached ADUs offer greater design control, privacy, and long-term functionality. They also allow for larger footprints, which opens up more livable space and better income potential.

Section 2: Permitting, Zoning, and Fire Access

Garage Conversions

Garage conversions are typically easier to permit. They qualify for setback exemptions under California state law, and LADBS reviewers focus more on habitability and structural upgrades than on site layout. If the garage is within half a mile of public transit, parking replacement is not required under Government Code §65852.2.

Because the structure already exists, fire access is rarely an issue. However, the garage must be legally permitted and appear in city records. Any prior unpermitted additions, such as illegal expansions or patio enclosures, may trigger code enforcement during review.

Detached ADUs

Detached units are more complex from a zoning and access standpoint. The Los Angeles Fire Code (Section 503.1.1) requires a minimum 3- to 4-foot clear path from the street to the ADU entrance. This path must be level, unobstructed, and meet surfacing standards.

State law mandates 4-foot minimum rear and side yard setbacks, but Los Angeles may impose additional limits based on lot configuration, overlays, or local plan areas. Detached ADUs must also maintain proper distance from the main house, often 6 feet or more, per Title 24 building code for fire separation.

Site constraints that may affect feasibility include:

• Recorded utility or drainage easements

• Sloped or irregular lots

• Limited access width for fire and egress

• Floor area ratio (FAR) and lot coverage limitations

Without a zoning analysis and site review, homeowners risk investing in plans that cannot be permitted as designed.

Section 3: Common Hidden Traps

Even with favorable ADU laws, several issues can delay a project or increase cost:

• Easements: Utility, sewer, or drainage easements often reduce buildable area. These are not always visible on assessor maps and require a title report or ALTA survey.

• Nonconforming Garages: Many older garages were built without permits or fall short of code. Cracked slabs, low ceilings, and unreinforced framing may require full reconstruction.

• Fire Access Restrictions: Lots without a compliant side yard or rear access may not qualify for detached ADU approval.

• Parking Replacement Requirements: If the property is outside transit zones or inside a Specific Plan Area, LADBS may still require replacement parking even for garage conversions.

The most reliable way to prevent surprises is to start with a code-based feasibility assessment.

Section 4: Design Flexibility, Privacy, and Livability

Garage Conversions

Garage conversions are ideal for quick, cost-effective builds. Most are completed in 3 to 5 months, depending on scope and condition. However, they are typically limited to 300 to 400 square feet, which can restrict layout options.

Because these units are often built near driveways, fences, or rear walls, they may lack natural light, outdoor space, or acoustic privacy. Garage conversions work well as guest suites, mid-term rentals, or compact housing for students or seniors. They are less ideal for long-term tenants or family members who require more separation.

Detached Units

Detached ADUs offer the most control over layout and livability. Units between 500 and 850 square feet can accommodate full kitchens, multiple bedrooms, and vaulted ceilings. Builders can orient windows and entries to maximize light and airflow while preserving privacy between households.

These units are particularly well-suited for long-term rental, family housing, or remote work. When properly designed, detached ADUs enhance both resale value and curb appeal. According to Freddie Mac, detached ADUs tend to generate more appraisal value than conversions, especially when they are permitted and metered separately.

Section 5: Rental Income and ROI

Garage Conversions

Garage ADUs in Los Angeles typically rent for $1,800 to $2,400 per month, based on data from Apartments.com and Zillow (May 2025). These units often break even in 4 to 6 years, assuming build costs remain under $135,000. ROI is particularly strong for owners who use a home equity line of credit (HELOC) or receive assistance through the CalHFA $40,000 ADU grant.

Detached Units

Detached ADUs rent for $2,400 to $3,800 per month, with two-bedroom units in Culver City and Westwood reaching over $4,000. While initial build costs are higher, so is long-term income potential. These units attract stable tenants and perform well in resale.

Here’s a simplified breakdown:

ADU Type	Build Cost	Rent Range	Annual Gross	Estimated Payback
Garage Conversion	$95K – $135K	$1,800 – $2,400	$21,600 – $28,800	4–6 years
Detached Studio	$140K – $180K	$2,000 – $2,700	$24,000 – $32,400	5–7 years
Detached 1-Bedroom	$180K – $230K	$2,400 – $3,200	$28,800 – $38,400	5.5–8 years
Detached 2-Bedroom	$240K – $300K	$3,000 – $3,800	$36,000 – $45,600	6.5–8.5 years

Figures reflect Los Angeles market conditions in 2025. ROI will vary based on financing, vacancy, and build quality.

Section 6: Which Approach Is Right for Your Property?

Choose a garage conversion if:

• You need a fast, low-cost project with modest square footage

• You have a legal, structurally sound garage

• The unit is for short-term use, guests, or family support

Choose a detached ADU if:

• You want layout control and long-term livability

• You plan to rent full-time or house family members for years

• Your lot has sufficient access, setbacks, and buildable area

Final Thoughts

There is no single right answer when deciding between a garage conversion and a detached ADU. Both options offer meaningful benefits, but they serve different goals and come with different constraints. Garage conversions are typically faster to build, more affordable to permit, and well-suited for homeowners with a structurally sound garage and a need for compact living space. Detached ADUs require more investment but provide superior design flexibility, privacy, and long-term income potential.

The best choice depends on a combination of factors: your budget, your lot’s zoning and fire access requirements, your intended use for the unit, and how much livable space you actually need. Site-specific conditions like easements, slope, and utility layout can make or break a project and what works on one property may not be feasible just a few blocks away.

Before investing in design plans or submitting permits, it’s important to take a close look at what your site can realistically support. A feasibility study, early consultation with a qualified professional, or a thorough zoning and code review can help identify obstacles and streamline the process. Taking these steps early can save time, prevent costly revisions, and ensure that the ADU you envision aligns with both your goals and what the city will allow. Whether you’re planning for rental income, family housing, or long-term property value, starting with the right approach will set your project up for success.