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

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How Much Does Junior ADU & Interior Conversion Cost in San Antonio?

In San Antonio, a junior ADU (JADU) or interior conversion typically costs between $45,000 and $95,000 in 2026, with most homeowners landing around $65,000 to $80,000 for a finished, permitted unit with a kitchenette and private entrance. A basic bedroom-to-JADU conversion with minimal plumbing work starts near $40,000, while a full garage interior conversion with upgraded finishes in neighborhoods like Alamo Heights or Terrell Hills can push past $110,000. You’ll get a written price before any work starts with Benson ADU San Antonio, so the number you see is the number you pay.

This guide breaks down exactly where the money goes, what drives costs up or down in the San Antonio market, and how to avoid the pricing games that plague this category of construction. If you’re weighing a JADU against a full detached ADU, or deciding whether to convert an existing garage interior versus build new, we’ll give you real numbers to work with.

Before we dive in, a quick note on terminology. A junior ADU (legally a JADU) is a smaller dwelling unit, typically under 500 square feet, created within the existing footprint of a single-family home. An interior conversion is the actual building process: taking an existing garage, basement, attic, or underused room and converting it into a legal, rentable living space with its own entrance, kitchenette, and sometimes its own bathroom. In Texas, JADUs go by different names at the local level, but San Antonio’s Development Services Department generally treats them as accessory dwelling units under the city’s Unified Development Code. That means setbacks, lot coverage, and owner-occupancy rules all come into play. We walk every homeowner through this paperwork as part of the project scope.

Key takeaways before the details:

• Most JADU and interior conversion projects in San Antonio range from $45,000 to $95,000.
• Cost per square foot runs $120 to $230 for interior conversions, depending on plumbing, electrical, and finish level.
• Prefab panel systems from brands like Abodu, Cover, and Plant Prefab can cut weeks off a JADU timeline and reduce labor costs by 15 to 25 percent versus site-built framing.
• San Antonio’s permit fees for ADUs and JADUs typically add $2,500 to $6,000 depending on valuation and whether utility upgrades are required.
• Benson ADU San Antonio puts every price in writing before a single shovel turns. Call (430) 258-2928 for a free estimate.

Junior ADU & Interior Conversion Cost Breakdown (2026)

Here’s the honest math on where your money goes. These ranges reflect what we’re seeing on actual San Antonio projects in 2026, from modest 350-square-foot JADUs in Jefferson and Woodlawn Lake to full 750-square-foot garage conversions in Stone Oak and Alamo Ranch.

Total realistic range: $45,000 to $115,000, with most San Antonio JADU and interior conversion projects finishing between $60,000 and $85,000.

Now, here’s what actually drives those numbers. San Antonio has some quirks that don’t show up in national ADU cost guides. The city sits on a mix of limestone bedrock and expansive clay soils. In neighborhoods like Castle Hills and Hill Country Village, the clay-heavy soil can shift seasonally, which means foundation work sometimes requires piering or additional slab reinforcement before you even think about framing. In older neighborhoods like Monte Vista or King William, homes built before 1970 often have electrical panels that won’t pass inspection for a new ADU circuit load, so a $3,500 panel upgrade gets added to the scope. And the Texas heat is not a suggestion: a poorly insulated JADU in a west-facing garage can hit 110 degrees in August. We spec mini-split systems and upgraded insulation as the standard, not the upsell.

What Affects Junior ADU & Interior Conversion Pricing in San Antonio

Every project is different, but these are the six factors that move the needle most on your final number. Understanding them before you start means fewer surprises and a better conversation with any contractor.

• Plumbing proximity. If the garage or interior space you’re converting sits on the same side of the house as the main sewer line and water supply, your plumbing costs stay in the $7,000 to $10,000 range. If the sewer line runs across the house, or if slab cutting is required to move drain lines, expect $15,000 to $22,000. This is the single biggest cost variable in JADU projects.
• Electrical capacity. San Antonio homes built before 1990 often have 100-amp panels. A JADU with a mini-split, kitchenette appliances, and a bathroom can require 60 to 100 amps on its own, which means upgrading to a 200-amp panel at $3,500 to $6,000 before you add branch circuits.
• Prefab versus site-built. Prefab panel systems from Abodu, Cover, and Plant Prefab arrive with walls, windows, and doors already assembled. That reduces framing labor by 15 to 25 percent and cuts total build time from 16 to 24 weeks down to 8 to 14 weeks. The material cost runs higher upfront, but the labor savings net out in your favor, especially with current San Antonio construction labor rates.
• Foundation condition. Garage slabs in San Antonio were not always poured with the intention of becoming living space. Many older slabs lack a vapor barrier, which means moisture can wick up through the concrete and into your new flooring. Adding an epoxy moisture barrier and sleeper-floor system runs $4 to $8 per square foot. It’s a real cost, and it’s one that cheap bids conveniently omit.
• Interior finish level. A basic JADU with builder-grade fixtures, LVP flooring, and a simple kitchenette runs near the bottom of the range. Quartz countertops, custom cabinetry, tile showers, and upgraded lighting packages can add $15,000 to $30,000 on their own. We’ll show you the difference on paper so you choose deliberately, not by surprise.
• City permit and utility requirements. San Antonio’s Development Services Department requires a full permit package for any JADU conversion, including stamped drawings and a plumbing inspection. If your property is in a historic district like Monte Vista or King William, you’ll also need a Certificate of Appropriateness from the Office of Historic Preservation, which adds 4 to 8 weeks to the timeline and $1,500 to $4,000 in additional design and review fees.

JADU vs. Detached ADU: Which One Costs More in San Antonio?

A full detached ADU in San Antonio typically runs $180,000 to $350,000 for a 500 to 1,000 square foot unit built in the backyard. A JADU or interior conversion runs $45,000 to $115,000 because you’re using existing walls, a roof, and a foundation. The trade-off is size and privacy: a JADU caps out around 500 square feet by state definition, while a detached ADU can go larger and gives the renter or family member their own front door with true separation. If your main goal is rental income, a detached ADU typically commands 30 to 40 percent higher rent per month. If your goal is housing a family member affordably, a JADU is the fastest path to a legal, comfortable unit without breaking six figures.

Our team builds both. When you call (430) 258-2928, we’ll walk you through the numbers for your specific property, including what makes sense based on your lot size, existing structure, and what you’re trying to achieve.

What You Get With a Benson ADU San Antonio JADU Project

Here’s the part most contractor websites won’t tell you. The price is only half the story. The other half is whether the price holds, whether the crew shows up, and whether the work lasts.

The written price is the actual price. Every Benson ADU San Antonio project starts with a line-item written quote before any work begins. Not a verbal estimate. Not a range with a wink. A written document you can hold us to. If we discover something hidden during construction, we bring it to you with options and a number before we touch it. You approve or decline. No scope creep, no “surprise” invoices at the end.

The 365-Day Done Right Promise. If anything on your JADU project isn’t done right within a full year of completion, we make it right. This isn’t a handshake promise. It’s written into every contract, stamped on every project file, and backed by a free second visit if any covered repair fails. You get this in writing before construction starts.

Brands you can verify. We’re authorized to build with Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, and Tuff Shed, and we source exterior cladding from James Hardie. You’re not stuck with whatever a contractor happens to have in the yard. These are national brands you can research independently, read reviews on, and verify quality yourself before you commit.

Transparency from day one. Our technicians are background-checked and arrive in uniform. You get real-time updates on progress, before-and-after photos, and a digital invoice you can pay by link. A live person answers our phone 24/7. No voicemail loops. When you call to ask where your project stands, you talk to a human who knows the answer.

All of this rolls up under The Relay Visibility Guarantee, the standard we’ve held since our parent company, Relay Home Co., was founded in 2006. Each Benson location is independently owned and operated, but every one operates under the same written promise: the price you see is the price you pay, the work is done right, and the guarantee is in writing.

How to Save on Junior ADU & Interior Conversion in San Antonio

Saving money on a JADU isn’t about finding the cheapest bid. Cheap bids in San Antonio usually mean one of three things: the contractor isn’t pulling permits, the contractor is going to hit you with change orders once demo starts, or the contractor is cutting corners on insulation and waterproofing that you’ll pay for in the San Antonio heat for years to come. Here’s how to actually save without sacrificing the outcome.

1. Convert existing space instead of adding on. The most expensive square footage in any home addition is the new foundation and roof. A garage interior conversion, attic conversion, or large walk-in closet conversion skips those costs entirely. That’s why a JADU routinely costs half to a third of what a detached ADU costs per square foot.
2. Choose a prefab panel system. Abodu, Cover, and Plant Prefab deliver pre-assembled wall panels that cut site labor by 15 to 25 percent. On a $70,000 project, that’s $10,000 to $17,000 saved on framing and installation labor, plus a shorter timeline that saves you weeks of project management overhead.
3. Keep the layout tight around existing plumbing. If your washer/dryer hookup or an existing bathroom sits adjacent to the space you’re converting, design your JADU kitchenette and bath to tap into those lines. Avoiding slab cutting and long drain runs can save $5,000 to $10,000 on a typical San Antonio project.
4. Phase the finishes. Build the JADU shell complete with plumbing, electrical, HVAC, and drywall, but install budget-level flooring and fixtures now. You can upgrade to quartz, custom tile, and higher-end lighting in year two or three as rental income accumulates. Just make sure the rough-in work (plumbing stubs, electrical capacity, insulation) is done right the first time, because retrofitting those later costs far more.
5. Get multiple written comparisons. You wouldn’t buy a car from a verbal description of the price. Don’t accept one for a construction project. Get at least three written quotes. We’ll give you one free, with the same line items every homeowner gets, and we encourage you to compare it against other written bids. When prices are in writing, the differences in scope become obvious.

For an exact price on your specific San Antonio property, call (430) 258-2928. Estimates are free, and you’ll have a written number before you ever make a decision.

Learn more about what goes into a JADU project on our Junior ADU & Interior Conversion in San Antonio page, or start from our home page to explore all the services we offer.

FAQs – Junior ADU & Interior Conversion Cost

How much does a JADU cost per square foot in San Antonio?

A junior ADU or interior conversion in San Antonio runs $120 to $230 per square foot in 2026, depending on whether the space is a straightforward room conversion or a full garage conversion with new plumbing and HVAC. A 400-square-foot JADU at $160 per square foot lands around $64,000. Call (430) 258-2928 for an exact quote based on your specific space and scope – estimates are free.

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

Converting an existing garage interior runs $45,000 to $95,000, while building a new detached ADU runs $180,000 to $350,000. The garage conversion wins on cost because you’re reusing the foundation, walls, and roof. The detached ADU wins on long-term rental value and privacy. We’ll help you run both scenarios for your property so you can see the numbers side by side.

Can a JADU be built in under 6 months in San Antonio?

Yes. A prefab-based JADU using Abodu, Cover, or Plant Prefab panels typically completes in 8 to 14 weeks from permit approval to final inspection. Site-built conversions take 16 to 24 weeks. San Antonio’s permit review for ADU projects currently runs 3 to 6 weeks for standard applications, and historic districts add 4 to 8 weeks. We handle all permit paperwork as part of the project.

What does San Antonio charge for ADU permit fees?

San Antonio ADU and JADU permit fees typically run $2,500 to $6,000 depending on project valuation, with additional water and sewer impact fees of $1,500 or more if a second meter is required. The exact number depends on the scope of your project and whether you’re in a historic district. We include a line-item breakdown of every fee in your written quote, so there’s no mystery on the final bill.

Do JADUs add value to a home in San Antonio?

In San Antonio’s 2026 market, a permitted JADU adds between $55,000 and $90,000 to a home’s resale value, which is roughly 80 to 100 percent of what you’ll spend to build it. The stronger financial argument is income: a 400-square-foot JADU in a desirable neighborhood like Alamo Heights or Monte Vista rents for $950 to $1,400 per month, which pays back the construction cost in 4 to 6 years at current rent rates.

Does Benson ADU San Antonio offer financing?

Yes. We work with multiple lenders that specialize in ADU construction financing, and we can connect you with options ranging from renovation loans to energy-efficiency programs. Every financing path starts with the same written price, so your lender sees the exact same number you do.

Get a Written Price for Your San Antonio JADU Project

The fastest way to know exactly what your junior ADU or interior conversion will cost is to talk to us. You’ll get a line-item written price, a realistic timeline, and straight answers about what your specific property requires. No verbal estimates that change later. No pressure to sign today. Just a real number from a builder who puts it in writing.

Call (430) 258-2928 for your free estimate. Someone will answer, day or night.

Pricing reflects the San Antonio market as of 2026. Benson ADU San Antonio offers free estimates – call (430) 258-2928.