New Detached ADU Cost - Plans, Permits & Build, One Fixed Price

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How Much Does New Detached ADU Cost in San Antonio?

A new detached ADU in San Antonio typically costs between $185,000 and $325,000 for a turnkey project in 2026, with most one-bedroom units landing in the $195,000 to $240,000 range. That breaks down to roughly $250 to $410 per square foot depending on finishes, site conditions, and whether you go prefab or site-built. Prefab options from brands like Abodu and Dvele tend to run 10% to 20% below comparable site-built construction because the factory process cuts framing and weather-delay costs.

These numbers reflect what we’re seeing across Bexar County this year, from Alamo Heights to Stone Oak to the growing corridors west of Loop 1604. Every project is different, but this guide gives you the real ballpark so you know what to expect before you call anyone. And if you want a written price for your specific lot, call Benson ADU San Antonio at (430) 258-2928 for a free estimate.

New Detached ADU Cost Breakdown (2026)

Here’s a line-by-line look at where the money goes on a typical detached ADU in the San Antonio market. These are the numbers we quote from, not national averages pulled from a database.

Total turnkey range: $185,000 – $325,000. Most homeowners we work with in San Antonio land between $210,000 and $260,000 for a completed, rent-ready or move-in-ready detached ADU with high-quality-but-not-luxury finishes.

Site-Built vs. Prefab: What Changes the Price

In San Antonio, site-built ADUs (stick-frame construction done on your lot, start to finish) run $275 to $410 per square foot. Prefab options using brands like Abodu, Dvele, Mighty Buildings, and Plant Prefab usually come in at $250 to $340 per square foot including delivery, crane, and finishing trades. A 600-square-foot one-bedroom site-built ADU might cost $250,000, while the same square footage through a factory-built system could land closer to $195,000 to $215,000 depending on the model and site access.

Boxabl and Tuff Shed represent the lower end of the spectrum. Boxabl’s folding Casita units start around $60,000 to $80,000 for the unit itself, but you still need foundation, utility connections, permits, and finish-out, which usually adds $70,000 to $110,000 in San Antonio. Tuff Shed structures, converted for living use, can work for a studio in the $90,000 to $130,000 range, though they require substantial upgrade work to meet residential code under the City of San Antonio’s ADU ordinance.

What Affects New Detached ADU Pricing in San Antonio

Two identical 600-square-foot ADUs can land $60,000 apart depending on these factors. Here’s what actually moves the number in the San Antonio market:

• Lot access and set-back conditions. A detached ADU in an older neighborhood like Monte Vista or Beacon Hill often faces a narrow side yard, mature trees, and a 5-foot side and rear setback requirement. If a crane or a large foundation dig can’t access the back of the lot, labor costs climb. Flat, open lots on the northeast side (Converse, Kirby, Schertz area) are cheaper to build on.
• Utility runs. The distance from your main house’s water, sewer, and electrical panel to the ADU’s location directly drives trenching and wire costs. Every extra 20 feet of trench adds somewhere around $1,800 to $3,000 in combined costs.
• Kitchen size and type. A kitchenette (sink, under-counter fridge, microwave) runs $8,000 to $14,000. A full kitchen with a range, dishwasher, standard fridge, and 12 linear feet of cabinetry runs $18,000 to $30,000. If the ADU is meant for rental income, most San Antonio landlords go full kitchen and that decision alone adds $10,000 to $16,000 to the bottom line.
• Foundation complexity. Most detached ADUs in Bexar County go on slab-on-grade. But parts of the Hill Country fringe (Helotes, Grey Forest, Timberwood Park) have shallow rock or significant grade changes that push foundation costs up 25% to 40% versus a flat city lot.
• Bathroom count and placement. A single bathroom with a basic fiberglass surround is the budget-friendly path. Adding a second bath, or going to tiled showers and a freestanding tub, can move the price by $12,000 to $22,000. Prefab ADU models from Dvele and Cover include premium baths in their base specification, which is part of why their per-square-foot cost reads higher but their included-finish value is stronger.
• San Antonio’s permitting and inspection rhythm. The City of San Antonio Development Services Department processes ADU permits through the same residential path as home additions. Plan review currently runs 4 to 8 weeks for a straightforward detached ADU application, and inspections happen on a schedule that varies by inspector workload. Delays add construction loan interest if you’re financing the build, which quietly raises your true project cost.

How to Save on New Detached ADU

You can’t change the city’s permit fees or what a plumber charges in Bexar County, but you can control a surprising amount of the total.

1. Choose a prefab platform with the right base spec. Brands like Abodu and Cover include things like millwork, lighting, appliances, and even furniture-level finishes in their base models. When the base price already covers most of the inside, you avoid the slow bleed of change orders and finish upgrades that plague site-built projects.
2. Keep the footprint simple. Every corner, bump-out, and shed roof transition adds framing labor and roof complexity. A rectangular 600-square-foot ADU costs measurably less per square foot than a 600-square-foot L-shaped plan with a vaulted ceiling.
3. Do the numbers on a one-bedroom versus a studio. The difference in cost between a 400-square-foot studio and a 600-square-foot one-bedroom can be $60,000 to $90,000, but the rent difference in most San Antonio neighborhoods is only $300 to $500 a month. If the ADU is for income, the studio often pencils out faster.
4. Site the ADU close to the existing house. Cutting the utility trench distance from 80 feet to 25 feet saves real money. It also often keeps you further from the rear lot line, which simplifies setback compliance.
5. Lock a written price before you start. Verbal estimates shift. They always do. Benson ADU San Antonio provides a written price before any work starts, and that’s exactly why the number you approve is the number you pay. No scope creep billed after the fact. Call (430) 258-2928 for a free estimate and the math on your property.

Why Prefab Brands Change the San Antonio Price Equation

You should know the names and what they mean for your budget. At Benson ADU Builders, we’re authorized to build with Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, and Tuff Shed, with James Hardie cladding as a standard exterior option. That matters because each one occupies a different cost tier and delivers different speed-to-occupancy.

Abodu builds compact ADUs (studio to two-bed) in a factory and installs them in about three weeks on site after foundation and utilities are ready. In San Antonio, an Abodu one-bedroom typically totals $190,000 to $250,000 all-in including site work.

Dvele positions as the high-performance brand, with steel-frame construction and deeply integrated smart-home systems. A Dvele detached ADU commonly starts at $280,000 and can pass $400,000 with options. It’s the choice when long-term durability and low operating cost are the priority.

Mighty Buildings uses a 3D-printed composite panel system that produces a tight, energy-efficient shell. Expect $260,000 to $340,000 for a completed unit. Plant Prefab works across the middle tier, offering panelized and modular systems in the $220,000 to $300,000 finished range.

Cover delivers high-end modular units with a design-forward ethos that frequently lands between $300,000 and $400,000 in San Antonio. Boxabl and Tuff Shed anchor the budget tier, with finished, code-compliant living costs in the $120,000 to $210,000 zone depending on configuration and finish-out path.

When you call Benson at (430) 258-2928, we’ll walk you through which of these systems is worth evaluating for your lot, your budget, and your timeline. Every option is presented with a written price so you’re comparing fixed numbers, not vague estimates.

San Antonio-Specific Costs You Won’t Find in a Generic Guide

Most cost guides online quote national averages that miss what actually happens here. These are the San Antonio realities:

• Heat is the hidden driver of your long-term cost. San Antonio sees 100-plus days of 90°F heat and your ADU’s cooling load is substantial. Spending $2,500 extra on a properly sized mini-split with a high SEER rating and good insulation will save you $600 to $900 a year in electricity versus a builder-grade system. That’s a six-year payback or less.
• Foundation movement is real here. The clay-heavy soils across much of San Antonio expand and contract through wet-dry cycles. A properly engineered slab with the right reinforcement and post-tension cables costs $3,000 to $6,000 more than a basic slab, but it’s the difference between an ADU that stays square for 30 years and one that cracks doors and tile lines by year three. This is one of the reasons Benson insists on engineered foundations for every detached ADU, even when the city minimum wouldn’t strictly require it.
• Rental demand varies by neighborhood. A one-bedroom ADU near the Medical Center rents for $1,400 to $1,800 a month. The same unit in a south-side neighborhood rents for $900 to $1,200. If rental income is your payback, the neighborhood math should guide your finish budget. A higher-end finish in a lower-rent area extends your payback period by years.
• ADUs remain legal and permitted in most San Antonio residential zones. The city updated its ADU rules in recent years to allow detached accessory units on most single-family lots. There are still size limits (generally 1,100 square feet or 50% of the main dwelling, whichever is less for most zones) and design standards. Benson handles the permitting as part of the project, and the permitting line in your written price covers it.

Financing a New Detached ADU in San Antonio

San Antonio homeowners typically fund an ADU one of five ways, and each carries different math:

• Cash-out refinance or HELOC. For homes bought or refinanced before 2022, many San Antonio homeowners hold sub-4% mortgages. A HELOC layered on top usually runs 7% to 9% in 2026. If the ADU rents for $1,500 a month, that carries a $200,000 build comfortably.
• Construction loan, then permanent mortgage. Local lenders and credit unions (SSFCU, RBFCU, Generations FCU offer construction-to-permanent products) lend against the post-build appraised value. Expect 20% down and rates around 6.5% to 8%.
• Renovation mortgage (FHA 203k or Fannie Mae HomeStyle). Both work for ADUs but add paperwork and time. HomeStyle is the better fit for most detached ADU projects.
• Cash. Roughly 30% of the ADU projects we price in the San Antonio area are cash-funded, often from savings or an inheritance.
• Personal loan for the smaller scope. If the project is a home addition-sized build under $100,000, a personal loan at 9% to 13% sometimes beats the closing costs of a full refinance.

Cost Per Square Foot: What San Antonio Actually Delivers

You’ll hear contractors toss out per-square-foot numbers, and most of them are useless without context. Here’s the real picture for new detached ADU construction in San Antonio in 2026:

• $250 – $300/sq ft: Prefab and panelized systems from Abodu, Plant Prefab, and the higher-spec Boxabl finish-outs. Includes standard finishes, modest kitchens, and typical site work on an accessible city lot.
• $300 – $360/sq ft: Quality site-built construction with solid finishes, full kitchens, and one to two bathrooms. This is the sweet spot for most San Antonio homeowners who want a rental-ready unit without luxury pricing.
• $360 – $450+/sq ft: Custom site-built or premium prefab (Dvele, Cover). High-end finishes, complex sites, or design-heavy plans. If your lot is on the Hill Country fringe with rock excavation or steep grades, this is where you land.

The economy of scale is real: a 400-square-foot studio hasn’t got enough square footage to spread the fixed costs (permits, utility connection, foundation, one-time site mobilization), so its per-square-foot number reads higher. A 900-square-foot two-bedroom spreads those fixed costs thin and lands closer to the bottom of the ranges above.

Timeline and What It Does to Your Budget

A detached ADU in San Antonio typically takes 9 to 14 months from first call to certificate of occupancy, broken down roughly like this:

• Design and permitting: 10 to 16 weeks. Plans, structural engineering, and City of San Antonio plan review. Prefab systems compress this phase because the manufacturer provides pre-engineered plans that sail through review faster.
• Site work and foundation: 3 to 5 weeks. Depends on utility trenching, soil conditions, and inspector availability.
• Construction and installation: 8 to 20 weeks. Site-built runs the longer end. A prefab unit from Abodu or Boxabl can be set and finished in 3 to 6 weeks after the foundation passes inspection.
• Final inspections and close-out: 2 to 4 weeks. City inspections, utility final connections, and your punch list walk.

Every month of delay adds carrying cost if you’re financing. That’s another reason prefab systems win on total cost even when their sticker price looks similar to site-built: you’re paying interest for fewer months and your tenant (or your mother-in-law) moves in sooner.

Benson ADU San Antonio: What You Get With Your Build

Troy Eastman leads Benson ADU San Antonio, and the process he runs reflects one principle: you should know exactly what you’re paying and exactly what you’re getting before a single shovel turns. That’s The Relay Visibility Guarantee, and it’s the framework behind every ADU project we take on in the San Antonio area.

Here’s what that means when you work with us on a new detached ADU:

• A written price before work starts. Not a verbal estimate, not a round number with a wink. A line-item price you can hold. If something changes, you approve it in writing before it happens.
• The 365-Day Done Right Promise. If any part of your ADU isn’t done right within a full year of completion, Benson makes it right. In writing, on every project.
• A free second visit if any covered repair fails. That’s part of the written guarantee, not a goodwill gesture.
• Background-checked, uniformed technicians on your job site every time. You’ll know exactly who is walking onto your property.
• A live person on the phone 24/7. Call at 2 a.m. with a question about your project and a person answers. No voicemail loop.
• Access to the industry’s leading prefab brands (Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed) and James Hardie materials, so you’re choosing from curated options instead of a single take-it-or-leave-it product.

Benson ADU Builders is part of the Relay Home Co. family, founded in 2006. Each Benson location is independently owned and operated under The Relay Visibility Guarantee, so you get the consistency of a national framework with the accountability of a local team that answers to you directly.

FAQs – New Detached ADU Cost in San Antonio

How much does a 600 sq ft ADU cost in San Antonio?

A 600-square-foot detached ADU in San Antonio typically costs $185,000 to $260,000 turnkey in 2026, depending on whether you choose a prefab system like Abodu or a site-built approach. Prefab versions of this size often land between $185,000 and $215,000, while site-built versions run $210,000 to $260,000. Call (430) 258-2928 for a written price on your specific lot, free of charge.

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

A garage conversion in San Antonio generally costs $90,000 to $160,000, which is $80,000 to $150,000 less than a new detached ADU at $185,000 to $325,000. But a conversion trades away your garage storage and parking, and the ceiling height, foundation work, and insulation upgrades on older San Antonio garages can eat into the savings quickly. If you value keeping the garage and building fresh, the detached ADU usually delivers better long-term rental income.

How much does a prefab ADU cost in San Antonio?

Prefab ADUs in San Antonio run $120,000 to $320,000 fully installed, depending on brand and size. A Boxabl Casita finished out typically lands at $120,000 to $190,000, an Abodu one-bedroom at $190,000 to $250,000, and a Dvele unit starts around $280,000. These totals include foundation, utility connections, delivery, and finish work, not just the factory price. Call (430) 258-2928 and we’ll price out the brands that fit your budget.

How long does it take to build a detached ADU in San Antonio?

Count on 9 to 14 months for site-built construction and 6 to 9 months for most prefab systems once design starts, including City of San Antonio permitting. A prefab ADU from Abodu or Boxabl, once the foundation and utilities are ready, can be set and finished in 3 to 6 weeks. Site-built framing, inspections, and finish trades simply take longer, and that extended timeline carries real financing cost.

Can I rent out a detached ADU in San Antonio?

Yes. San Antonio permits detached ADUs as rental units on most single-family residential lots, and one-bedroom ADUs in strong rental corridors (Medical Center, Alamo Heights, Stone Oak) typically fetch $1,400 to $1,800 a month in 2026. At a $220,000 build cost and $1,500 monthly rent, that’s a strong cash-flow profile before maintenance and vacancy. Benson handles the permitting on your ADU, and we can help you spec the unit for maximum rentability.

Do I need a permit for a detached ADU in San Antonio?

Yes, a detached ADU requires building permits, a site plan, and utility permits from the City of San Antonio. Permit and impact fees for a typical ADU project run $3,500 to $9,000, and the plan review typically takes 4 to 8 weeks. Benson ADU San Antonio includes all permitting costs in your written price, so there’s no line-item surprise after you sign.

Get a Written Price for Your San Antonio ADU

A new detached ADU is a six-figure decision, and you should not make it on a verbal estimate. Benson ADU San Antonio gives you a written, line-item price before any work starts, with the 365-Day Done Right Promise behind every project. We build with the best prefab brands in the industry and we’ll show you the cost difference between them in writing. Call (430) 258-2928 today for a free estimate, and talk to a real person who can answer your San Antonio-specific ADU questions on the spot.

Written by Troy Eastman, Owner at Benson ADU San Antonio, serving the San Antonio area with transparent ADU pricing and construction.

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