ADU, Casita, and Garage Conversion Costs in San Antonio
What an ADU, casita, or garage conversion costs in San Antonio — permits, timeline, and one veteran-owned licensed GC handling electrical, plumbing, and HVAC.
An ADU, casita, or garage conversion adds independent living space — for aging parents, rental income, a home office, or guests — on land you already own. It is a true multi-trade build: foundation, framing, electrical, plumbing, HVAC, and finishes under one permit-aware plan. C.S.W. Power Solutions is a veteran-owned licensed general contractor (VA Builder Registration #09311) that self-performs electrical (TECL31793), plumbing (RMP46592), and HVAC (TACLA26479R) in-house, so a San Antonio casita or garage conversion is handled by one accountable team instead of four separate subcontractors. This guide is part of the C.S.W. Power Solutions San Antonio homeowner library. Use the related links on this page to move from research into the matching licensed service page, compare connected trade requirements, and request a written estimate when the project needs plumbing, electrical, HVAC, generator, remodeling, restoration, or general-contractor coordination.
ADU, Casita, or Garage Conversion: What's the Difference?
These terms overlap, so it helps to define them. An accessory dwelling unit (ADU) is a second, smaller, fully independent living space on a single-family lot with its own kitchen, bathroom, and entrance. In San Antonio and across the Texas Hill Country, a detached ADU is often called a casita — a freestanding backyard cottage or guest house. An attached ADU shares a wall with the main home, such as a converted portion of the house or a unit over a garage. A garage conversion turns an existing attached or detached garage into finished, conditioned living space, and it is usually the fastest and most affordable path because the foundation, walls, and roof already exist. People also say granny flat, in-law suite, and backyard cottage for the same ideas.
What an ADU or Casita Costs in San Antonio (2026)
There is no single ADU price, because the work ranges from a light garage conversion to a fully detached casita with its own foundation and utility connections. As a planning framework, a garage conversion is typically the lowest-cost option, a detached casita built from the ground up is the highest, and an attached addition falls in between. The biggest cost drivers are square footage, the number of kitchens and bathrooms, foundation and site work, how far water, sewer, gas, and electrical service must be extended, whether your electrical panel has spare capacity, roofing and exterior materials, and finish selections. Because so much of the cost is hidden in site conditions and utility runs, the only honest number is a written, itemized estimate after a site visit, with labor, materials, trade work, and permits broken out.
Garage Conversion: The Lower-Cost Path to More Living Space
If your goal is more usable square footage without the cost of building from scratch, a garage conversion is usually the smartest starting point. The shell already exists, so the work focuses on what makes a space livable and code-compliant: insulation and air sealing, conditioned air from a ductless mini-split or extended ductwork, proper electrical circuits and outlets, replacing the garage door with a framed insulated wall and egress-compliant windows or a door, moisture control, flooring, drywall, and finishes. If you want a full ADU rather than a bonus room, you also add plumbing for a bathroom and kitchenette tied into water and drain lines. San Antonio's expansive clay soils and older slabs mean a conversion should start with an honest look at the slab, drainage, and framing before finishes go in.
Permits, Zoning, and the San Antonio UDC
ADUs, casitas, and garage conversions are permitted work, and skipping permits can create resale, insurance, and safety problems later. The City of San Antonio Development Services Department typically requires a building permit plus electrical, plumbing, and mechanical permits depending on scope, and inspectors verify the work at key stages. Whether you can build an ADU, and how large it can be, is governed by the city's Unified Development Code (UDC) and your property's zoning, which set rules for lot size, setbacks, building height, impervious cover, and parking. These rules vary by zoning district and lot, and the city has been actively revisiting its ADU regulations, so confirm current requirements for your specific address with Development Services before you design, and check any HOA or deed restrictions that may apply.
Why an ADU Is a Multi-Trade Project and Why One Licensed GC Matters
An ADU is essentially a small house, so it touches almost every trade. There is foundation and framing; electrical service, often a new sub-panel fed from the main panel; plumbing supply and drain lines tied into the home's system, sometimes a new gas line for a range or water heater; and HVAC, frequently a mini-split sized for the smaller load. When those trades are handled by separate companies, the homeowner becomes the project manager, chasing schedules and owning every delay. C.S.W. Power Solutions is a veteran-owned licensed general contractor that holds plumbing (RMP46592), electrical (TECL31793), and HVAC (TACLA26479R) licenses in-house under VA Builder Registration #09311 — one estimate, one schedule, one crew sequencing the trades correctly, and one company standing behind the finished casita.
How Long Does an ADU or Casita Take to Build?
Timeline depends on scope, design decisions, permit review, and inspections, but the phases are predictable. First comes design and planning, where layout, utilities, and budget are locked in. Next is permitting through the City of San Antonio, which takes time and should not be rushed. Then site work and a foundation for a detached casita, followed by framing, roofing, and the electrical, plumbing, and HVAC rough-ins that have to pass inspection before walls close up. Finally come insulation, drywall, finishes, fixtures, and final inspections. A garage conversion moves faster because the structure already exists, while a ground-up detached casita is a longer project. Finalizing design decisions early and using a contractor who self-performs the licensed trades keeps the schedule on track.
Does an ADU Add Value or Rental Income in San Antonio?
Homeowners build ADUs and casitas for multigenerational living — a private, accessible space for aging parents or adult children — for a long-term rental suite, a dedicated home office, or a comfortable guest house. A well-built, permitted ADU adds usable square footage and flexibility that many buyers value, though any effect on appraised value depends on the local market and how the space is finished and documented. If you are considering renting, note that San Antonio regulates short-term rentals through a city permitting process, and the rules and zoning vary, so confirm what is allowed for your property before counting on rental income. Building it permitted and to code protects the investment; an unpermitted conversion can become a liability at resale or with insurance.
Ready to Plan Your San Antonio ADU, Casita, or Garage Conversion?
The best first step is a conversation about your lot, your goals, and your budget. C.S.W. Power Solutions walks the property, talks through whether a detached casita, an attached addition, or a garage conversion fits best, flags the permit and utility considerations, and prepares a written, itemized estimate, with the electrical, plumbing, and HVAC handled in-house. As a veteran-owned licensed general contractor serving San Antonio, Stone Oak, Boerne, Helotes, Schertz, New Braunfels, and the surrounding Hill Country, CSW coordinates the whole project under one roof. Call 210-504-9796 or book an estimate online. Licensed plumbing (RMP46592), electrical (TECL31793), and HVAC (TACLA26479R); VA Builder Registration #09311.
Frequently Asked Questions
How much does an ADU or casita cost in San Antonio?
There is no single price. A garage conversion is typically the most affordable option, an attached addition is in the middle, and a detached, ground-up casita is the most expensive. Cost is driven by size, the number of bathrooms and kitchens, foundation and site work, how far utilities must run, electrical panel capacity, and finish level. Because so much depends on site conditions, the only reliable number is a written estimate after a site visit.
Can I build a casita or ADU in San Antonio?
In many cases yes, but it depends on your zoning and lot. The City of San Antonio's Unified Development Code and your property's zoning district govern whether an ADU is allowed and how large it can be, with rules for setbacks, height, lot coverage, and parking. The city has been revisiting its ADU rules, so confirm current requirements for your specific address with Development Services, and check any HOA or deed restrictions, before designing.
Do I need a permit to convert my garage in San Antonio?
Yes. Converting a garage into conditioned living space is permitted work and typically requires building, electrical, and mechanical permits, plus plumbing permits if you add a bathroom or kitchenette. Inspections verify the work meets code. Skipping permits can cause problems with insurance and at resale, so a garage conversion should be done as a permit-aware project, not an informal finish-out.
How long does it take to build an ADU or casita?
It varies with scope. A garage conversion is faster because the structure already exists, while a detached casita built from the ground up is a longer project that includes site work and a foundation. Every ADU moves through design, city permitting, rough-in inspections for electrical, plumbing, and HVAC, and final finishes. Finalizing design decisions early and using a contractor who self-performs the trades keeps the schedule on track.
Can I rent out an ADU in San Antonio?
Often yes for long-term rental, but short-term rentals are regulated by the City of San Antonio through a permitting process, and what is allowed varies by zoning and property. Confirm the current rules for your address before counting on rental income. In all cases, building the ADU permitted and to code protects you as a landlord and at resale.
C.S.W. Power Solutions is a veteran-owned, licensed general contractor serving San Antonio, TX and surrounding communities including Boerne, New Braunfels, Schertz, Stone Oak, Helotes, Alamo Ranch, Converse, Universal City, Live Oak, Leon Valley, Castle Hills, Cibolo, Seguin, and Southtown. Plumbing, electrical, HVAC, generator, EV charger, and remodeling trades all held in-house under one general-contractor license umbrella.
Call 210-504-9796, book online for a written estimate, or text photos so CSW can route plumbing, electrical, HVAC, generator, water heater, drywall, painting, restoration, or general contractor repair requests to the right crew.
Email cswpowersolutions@gmail.com. Located at 4931 Enterprise Drive, Suite 1, San Antonio, TX 78249. Business hours: Mon-Fri 7:00 AM - 6:00 PM, Sat 8:00 AM - 2:00 PM. Free written estimates within one business day.