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

Accessory Dwelling Units (ADUs) continue to gain popularity in Los Angeles for good reason. They can increase property value, generate rental income, and add much-needed living space. With new state laws making ADUs easier to permit, more homeowners are exploring the possibilities.

But one of the first and most important decisions to make is whether to convert an existing garage or construct a new detached unit. While both are legally supported under California ADU law, they involve different permitting processes, timelines, and long-term outcomes.

This guide walks through the key distinctions, focusing on cost, zoning, permitting complexity, and site constraints so you can make an informed choice before investing in design or submitting plans.

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

Garage Conversion

Garage conversions typically range from $95,000 to $135,000 in Los Angeles. These projects can be cost-effective because they reuse an existing structure. If the slab, walls, and framing are in decent shape, you may avoid major foundation or framing costs.

However, many garages were built before current code standards. Common problems include:

• Cracked or unreinforced slabs

• Insufficient ceiling height

• Unpermitted modifications

• Outdated electrical systems

These conditions may require substantial upgrades to bring the structure into compliance. According to the California HCD’s 2022 ADU Handbook, conversions are usually exempt from parking replacement if within a half-mile of public transit. That said, LADBS still reviews each property individually.

Detached ADU

Detached ADUs involve full ground-up construction, with typical costs ranging from $180,000 to $300,000 or more, depending on site conditions and finishes. The higher cost reflects the need for:

• New foundations

• Utility trenching

• Framing, roofing, insulation, and finishes

• Title 24 energy compliance

The California Residential Cost Guide places most new detached ADUs between $300 and $400 per square foot, though hillside lots or higher-end finishes may push those numbers higher.

Detached units allow for larger square footage, better privacy, and layout flexibility, but they also come with more permitting layers.

Section 2: Permitting, Zoning, and Fire Access

Garage Conversion Pros

In Los Angeles, garage conversions are generally more straightforward to permit. They often qualify for:

• Setback exemptions, since the structure already exists

• No parking replacement, if located within 0.5 miles of transit (per Gov Code §65852.2)

• Shorter plan check timelines, since design is limited to existing footprint

Because the structure is already permitted and within the existing development envelope, LADBS review typically focuses on:

• Structural integrity

• Habitability

• Energy code upgrades

• Legal status of the original garage

Detached ADU Watchouts

Detached ADUs are subject to full zoning review. That includes setbacks, fire access, and separation from the primary dwelling. Under Fire Code Section 503.1.1, the unit must have a 3- to 4-foot wide, unobstructed path from the street to the entrance.

Detached units must meet:

• Minimum 4-foot setbacks from rear and side lot lines

• 6 feet of building separation from the primary residence (per Title 24)

• Zoning overlays (such as Specific Plan Areas, hillside zones, or Historic Preservation Overlay Zones)

Without a clear fire access path, or if the build area is obstructed by utility lines or easements, plan check may require redesign.

Section 3: Common Permitting Pitfalls

Even straightforward projects can run into delays if the site isn’t evaluated early. These are some of the most common permitting issues TAPS sees:

• Easements: Utility or drainage easements can restrict where you can build. These are not always visible on assessor maps and require a title report or survey.

• Noncompliant Garages: If a garage is unpermitted or structurally unsound, LADBS may require demolition and rebuild.

• Fire Access Conflicts: Narrow side yards or obstructions can prevent detached units from meeting access code.

• Parking Replacement Requirements: Properties outside of transit zones or within Specific Plan boundaries may still trigger parking replacement for garage conversions.

🛠 Tip: Always start with a zoning check and parcel-specific code review before beginning design work.

Section 4: Design Flexibility, Privacy, and Livability

Garage Conversions

Garage conversions are usually limited to 300–400 square feet. They can often be completed in 3 to 5 months and are ideal for studios or compact one-bedroom layouts. These units are best suited for short-term stays, guest quarters, or modest rental income.

Design constraints include:

• Limited natural light

• Proximity to driveways or side yards

• Sound transmission from the main home

With thoughtful design, garage ADUs can be livable and attractive, but they may not offer the privacy or layout flexibility some tenants or family members need.

Detached ADUs

Detached units are far more customizable. They support:

• Larger footprints (500–850 square feet or more)

• Open layouts and multi-bedroom options

• Natural light through window placement and outdoor integration

These are ideal for long-term tenants, extended family, or work-from-home setups. Detached ADUs also tend to increase resale value more significantly than garage conversions, especially if metered and permitted independently.

Section 5: Rental Income and Return on Investment

Garage Conversions

Garage ADUs typically rent for $1,800 to $2,400 per month, depending on neighborhood, unit size, and finishes. According to May 2025 data from Apartments.com and Zillow:

• West Adams and El Sereno: frequently over $2,000/month

• North Hollywood: strong mid-range rental demand

These units generally recoup costs in 4 to 6 years, particularly when financed through a HELOC or paired with the CalHFA $40,000 predevelopment grant.

Detached ADUs

Detached ADUs rent for $2,400 to $3,800 per month, with some units exceeding $4,000 in Culver City or Westwood. While they cost more to build, they offer higher rents, stronger tenant retention, and better long-term equity.

ADU Type	Build Cost	Rent Range	Annual Income	Payback Period
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 gross rents. Net ROI will depend on taxes, financing, and vacancy.

Section 6: Which Option Fits Your Lot?

Choose a Garage Conversion If:

• You have a legal, structurally sound garage

• Your lot has limited buildable area or narrow access

• You want a cost-effective ADU with a short timeline

• You plan to house guests, students, or short-term tenants

Choose a Detached ADU If:

• Your lot meets fire access and setback rules

• You want more square footage and privacy

• Your long-term goal is rental income or multigenerational living

• You have flexibility in budget and build timeline

Final Thoughts

There is no universal answer when choosing between a garage conversion and a detached ADU. Each path comes with different tradeoffs in cost, code compliance, and long-term value.

Garage conversions are efficient and affordable, but limited in space. Detached units are more complex to permit and build, but offer stronger returns and livability. The right answer depends on your lot, your goals, and what Los Angeles zoning and fire code will allow. Before committing to design or financing, a site-specific feasibility review is the best way to move forward confidently. It can reveal code barriers early and ensure your ADU is not only buildable, but also approvable. If you're planning an ADU in Los Angeles, start with clarity start with the code.