Garage Conversion ADU Cost - Plans, Permits & Build, One Fixed Price

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How Much Does Garage Conversion ADU Cost in San Antonio?

A garage conversion ADU in San Antonio typically costs between $85,000 and $150,000 for a complete turnkey project in 2026, with most single-car conversions landing in the $95,000 to $120,000 range. That figure includes design, permits, plumbing, electrical, insulation, drywall, flooring, a kitchenette or full kitchen, and a bathroom. Prefab garage conversion systems from brands like Abodu and Boxabl can shift that range, sometimes lowering site labor costs while premium finishes and foundation work push the total higher.

This is the number homeowners ask us for first, and we’d rather put it in writing now than make you sit through a sales pitch to hear it. The final price on your specific garage depends on square footage, the condition of the existing slab, how much plumbing and electrical work is needed, and the finish level you choose. Keep reading for the full breakdown, including what drives cost up, what keeps it down, and what our written-price guarantee means for your project.

Key Takeaways:

• Typical San Antonio garage conversion ADU cost: $85,000 to $150,000, with most projects between $95,000 and $120,000.
• Cost per square foot runs $180 to $280 for a standard conversion, depending on finish level and existing condition.
• Prefab brands like Abodu, Boxabl, and Dvele change the math, offering fixed product pricing that can reduce on-site labor variance.
• Benson ADU San Antonio puts a written price in your hand before any work starts. No verbal estimate that shifts after demo day.
• Every project includes the 365-Day Done Right Promise, in writing, on paper.

Garage Conversion ADU Cost Breakdown (2026)

Here’s where the money goes on a typical San Antonio garage conversion. These are real working ranges based on projects we’ve priced in this market, not national averages pulled from a generic calculator. Your specific garage may fall above or below these lines depending on what’s already there.

Cost per square foot is another way to look at it. A 400-square-foot single-car garage converted at $180 to $280 per square foot lands between $72,000 and $112,000. A 600-square-foot two-car space runs $108,000 to $168,000. Smaller projects don’t mean proportionally smaller costs, because the fixed expenses (permits, design, plumbing connections, electrical service) don’t shrink much. That’s worth knowing before you decide between a studio layout and a one-bedroom.

Where San Antonio Specifically Moves the Price

Two things about this market affect garage conversion costs more than people expect. First, the existing slab. Many San Antonio garages were built on slabs that predate current moisture-barrier standards, and if water vapor is coming up through the concrete, you’ve got to address it before flooring goes down. That can add $3,000 to $8,000 depending on the fix, and it’s not a corner worth cutting. Second, the clay soil in Bexar County moves. Slabs shift over decades, and a garage that’s out of level by an inch or more needs correction work before framing. We flag this early because surprise slab repairs are one of the most common reasons a verbal estimate turns into a bigger bill later. Our written price includes a site inspection before we quote, so these issues surface on paper, not after demolition starts.

What Affects Garage Conversion ADU Pricing in San Antonio

The range between $85,000 and $150,000 is wide because every garage tells a different story. Here are the factors that move your number within that range.

• Garage size and layout. A 400-square-foot single-car garage costs less in total than a 600-square-foot two-car, but the cost per square foot is usually higher on the smaller one. Fixed costs like permits and utility connections spread differently.
• Slab condition and leveling. San Antonio’s expansive clay soil shifts slabs over time. If your garage floor has cracked, settled, or lacks a vapor barrier, budget an extra $3,000 to $12,000 for correction and moisture protection before any finished floor goes in.
• Plumbing distance from the main house. If the garage is attached and near existing drain lines, plumbing is straightforward. A detached garage 40 feet from the main waste line means trenching, and trenching in San Antonio’s rocky soil is slow work. That can add $5,000 to $10,000.
• Electrical capacity. Older San Antonio homes often have 100-amp panels that were never meant to carry an additional dwelling’s load. If you need a service upgrade or a new subpanel, add $2,500 to $6,500.
• Finish level. A rental-ready studio with LVP flooring, a kitchenette, and a three-quarter bath sits at the lower end. A one-bedroom with a full kitchen, custom cabinets, tile shower, and higher-end finishes pushes toward $150,000 and beyond. Material brands matter too, and James Hardie cladding or premium fixtures move the needle.
• Prefab vs. site-built components. We build with leading prefab brands including Abodu, Cover, Dvele, Mighty Buildings, Boxabl, and Plant Prefab. A prefab ADU panel system can compress the framing and finish timeline, which reduces labor variance. Site-built gives you more layout flexibility. The right choice depends on your garage’s dimensions and what you want inside.

Prefab Options: What Changes When You Choose a System-Built ADU

One thing that separates our approach from a traditional garage-conversion-only contractor is that we’re authorized to build with prefab systems from brands you can research yourself. Here’s what that means in practical terms for your budget.

Abodu builds fully finished modules that arrive on-site and get placed on a prepared foundation. For a garage conversion scenario, Abodu’s panelized approach works when the existing garage structure gets fully removed and replaced with a factory-built unit. Fixed pricing from the factory means fewer on-site labor hours and fewer change orders.

Boxabl is known for its Casita, a 361-square-foot foldable unit that arrives nearly complete. If your project is a detached structure rather than converting the existing garage, Boxabl changes the cost conversation entirely, because the unit price is fixed and the variable is site work.

Dvele and Plant Prefab sit at the higher end of the prefab spectrum with a focus on energy performance and healthier materials. Mighty Buildings uses 3D-printed panels for faster assembly. Tuff Shed provides the shell that some homeowners finish themselves, though we recommend full finish by a licensed contractor for a permitted ADU with plumbing and electrical.

The trade-off: prefab compresses time and locks in product pricing, but it constrains layout flexibility. A site-built conversion of your existing garage lets you work with the space as it is. We’ll show you the numbers for both approaches before you commit, in writing, so you’re choosing with real data instead of a sales deck.

How to Save on Garage Conversion ADU

You don’t need to cut corners to bring the number down. You need to make decisions early and keep the scope tight. Here’s what actually works in the San Antonio market.

• Keep the footprint as-is. The moment you expand beyond the existing garage walls, you’re into addition territory, which means more foundation work, more framing, and more permit complexity. Converting within the existing shell is the single biggest cost control.
• Choose a kitchenette over a full kitchen. A kitchenette with a sink, compact refrigerator, and microwave saves $8,000 to $15,000 compared to a full kitchen with a range, vent hood, and dishwasher. If your ADU is for a family member or short-term rental, that may be all you need.
• Standardize finishes. LVP flooring instead of tile, stock cabinets instead of custom, and a fiberglass shower surround instead of a tiled shower can drop the total by $5,000 to $10,000. These are choices you can upgrade later without structural disruption.
• Confirm the slab early. A slab inspection before you commit to a design tells you whether you’re facing a $3,000 fix or a $12,000 one. Knowing early means you can plan around it instead of absorbing it mid-project.
• Get a written price before you sign anything. This is the one that protects your budget more than any finish decision. A verbal estimate is a guess. A written price is a commitment. Every Benson ADU San Antonio project includes a written price before work starts, no exceptions, and no scope creep billed after the fact.

If you want to talk through where your specific garage falls in these ranges, call (430) 258-2928. We’ll walk the site, check the slab, look at the plumbing and electrical situation, and hand you a written price. Estimates are free, and there’s no pressure to commit on the spot.

FAQs – Garage Conversion ADU Cost

How much does a garage conversion ADU cost in San Antonio?

Most garage conversion ADUs in San Antonio cost between $85,000 and $150,000 for a complete turnkey project in 2026. Single-car conversions with standard finishes land in the $95,000 to $120,000 range. Your exact number depends on slab condition, plumbing distance, and finish level. Call (430) 258-2928 for a written quote on your specific garage, free.

Is it cheaper to convert a garage or build a new ADU in San Antonio?

A garage conversion is typically 20% to 35% cheaper than building a new detached ADU of the same size, because the foundation, framing, and roof already exist. In San Antonio, a new 400-square-foot detached ADU runs $130,000 to $180,000, while converting a 400-square-foot garage runs $85,000 to $120,000. The savings come from not paying for a new slab, new exterior walls, and a new roof structure.

How long does a garage conversion ADU take in San Antonio?

A standard garage conversion ADU takes 3 to 6 months from permit submittal to final inspection, with 2 to 4 months of that being active construction. Prefab approaches using brands like Abodu or Boxabl can compress construction time significantly once site preparation is complete. The design and permitting phase adds 4 to 8 weeks depending on the City of San Antonio’s current review volume. We provide real-time tracking so you always know where your project stands.

Can I rent out a garage conversion ADU in San Antonio?

Yes, garage conversion ADUs built with proper permits can be rented as long-term rentals or, with the right licensing, as short-term rentals in San Antonio. The city’s ADU ordinance, updated in recent years, allows ADUs in most residential zoning districts. Rental income potential is one of the main reasons homeowners convert garages, and in San Antonio neighborhoods like Alamo Heights, Terrell Hills, Beacon Hill, and Dignowity Hill, a finished ADU can generate meaningful monthly rent. We build every conversion to meet rental code requirements, not just minimum habitation standards.

What permits do I need for a garage conversion ADU in San Antonio?

You’ll need a building permit, and depending on scope, electrical, plumbing, and mechanical permits from the City of San Antonio Development Services Department. Your project must also comply with the city’s ADU standards, which address setbacks, parking replacement, and maximum unit size. Permit and impact fees on a garage conversion ADU in San Antonio typically run $3,500 to $7,500. Our project scope includes permit management, so you’re not chasing paperwork yourself.

Does Benson ADU San Antonio offer financing for garage conversions?

Benson ADU San Antonio provides written pricing you can take to any lender, and many homeowners finance their conversion through renovation loans, HELOCs, or cash-out refinances. Because our pricing is written and itemized before work starts, lenders can underwrite the project with real numbers instead of estimates. We’re also part of the Relay Home Co. family, founded in 2006, and our written guarantee on every project gives lenders and homeowners documentation that the work is backed.

Why the Written Price Matters as Much as the Price Itself

Here’s the part of this guide that matters most, and it’s not another line item. Most contractors in San Antonio will give you a verbal estimate. Then they discover something mid-project, and the number changes. That’s not necessarily dishonesty, but it’s not transparency either. You shouldn’t be financing someone else’s discovery process.

Benson ADU San Antonio, led by Troy Eastman, operates under The Relay Visibility Guarantee. That means a written price before any work starts, no exceptions. It means real-time tracking so you see exactly where your project is, not voicemail updates. It means background-checked, uniformed technicians on your property, so you know who’s walking through your gate. And it means a 365-Day Done Right Promise: if the work isn’t right within a full year, we make it right, backed by a written guarantee stamped on every project.

We’re authorized to build with Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, and Tuff Shed, and we use James Hardie materials where cladding is part of the scope. Those names matter because they’re verifiable. You can look up every one of them and see exactly what product quality you’re getting. We don’t hide behind “builder-grade” vagueness.

If you’re ready to turn your garage into living space, a rental unit, or a workspace, start with a real number, not a guess. Call us at (430) 258-2928 for a free written estimate. A live person answers every call, 24/7, and we’ll schedule a site visit that fits your timeline. You’ll get the price in writing before any commitment, and you’ll know the plan before a single shovel turns.

For more on what a garage conversion involves from start to finish, see our full guide on Garage Conversion ADU in San Antonio. Or return to our home page to explore everything we build.

Written by Troy Eastman, Owner at Benson ADU San Antonio. Pricing reflects the San Antonio market as of 2026. Benson ADU San Antonio offers free estimates – call (430) 258-2928.