ADU Permits, Codes & Inspections in TX: What You Need to Know

ADU Permits, Codes & Inspections in TX: What You Need to Know

Most homeowners start their ADU research by searching “Texas ADU laws” and immediately hit a wall. Texas has no statewide accessory dwelling unit statute, no blanket right-to-build, and no single codebook that tells you what’s allowed on your lot. What actually governs your project is a three-track system in San Antonio: the Unified Development Code (UDC) for zoning, CPS Energy for electrical and gas service, and San Antonio Water System (SAWS) for water and sewer connections. Each track has its own application process, its own inspectors, and its own timeline. Miss any one of them and a project that looked ready to break ground stalls for six to eight weeks. Our complete guide to ADU in San Antonio walks through each track in the order you’ll actually encounter them.

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Quick Answer

ADU permits in San Antonio are governed by Chapter 35 of the city’s Unified Development Code, not by state law. You’ll need a zoning verification letter first, then a building permit from Development Services, then separate utility applications with CPS Energy and SAWS. Expect the full process to take 4 to 8 months from first submittal to certificate of occupancy, depending on whether your lot triggers historic review or drainage complications.

Table of Contents

• Step 1: Finding Your San Antonio Zoning District and What It Allows
• The Three Documents You Actually Need (And the Order They Come In)
• CPS Energy and SAWS: Utility Connections That Run on Their Own Clocks
• Historic District Review: What Triggers It and What It Costs in Time
• The Inspection Sequence: What Gets Checked and How Long Each Step Takes
• What ADU Permits and Fees Cost in San Antonio in 2026
• Common Mistakes to Avoid
• When to Call a Professional
• Frequently Asked Questions
• The Bottom Line

Step 1: Finding Your San Antonio Zoning District and What It Allows

San Antonio’s UDC divides the city into zoning districts that each carry specific rules for accessory dwellings. The first number to know is your lot’s impervious cover percentage, because that single figure determines whether an ADU fits on your property at all before you ever think about walls or rooflines. Impervious cover means surfaces that shed water rather than absorb it: roof area, driveways, patios, walkways. In most single-family residential districts in San Antonio, total impervious cover on a lot is capped between 45% and 60%, depending on the district.

Here’s how to find your district in under ten minutes:

1. Open the City of San Antonio’s Zoning Map on the Development Services website. Enter your street address and note the district code that appears, typically something like R-4, R-6, NP-10, or similar.
2. Pull up Section 35-310 of the UDC, the table that lists accessory dwelling standards by district. This table tells you the maximum accessory structure height, side and rear setbacks, and minimum distance from the primary home.
3. Check the same table for the maximum lot coverage column. Add your existing home’s footprint, driveway, and any detached garage to your planned ADU footprint. If the total exceeds the cap, you’ll need a variance from the Board of Adjustment, which adds about 6 to 10 weeks and costs roughly $500 in filing fees.
4. Note whether your district even permits accessory dwellings. Most R-4, R-5, and R-6 districts in San Antonio do, but some neighborhood conservation districts restrict them. If you’re in a historic district, see the section on historic review below before spending a dollar on design work.

In R-5 and R-6 zones, which cover large swaths of the city inside Loop 410 and into the inner West Side and East Side, detached ADUs are generally capped at one story and roughly 30 feet in height, with a rear setback of at least 5 feet and side setbacks between 5 and 10 feet depending on lot width. Neighborhoods like Highland Park, Beacon Hill, and Dignowity Hill fall under these rules, with older platted lot sizes often meaning a 900-square-foot side yard that shrinks pretty quickly once you back out the setback math. We regularly sit down with homeowners who’ve sketched a 700-square-foot ADU only to realize the buildable envelope on their lot is closer to 550, one of the ADU warning signs San Antonio homeowners should watch for. A zoning verification letter (the first document you’ll file, covered next) confirms your exact numbers before any money goes into construction drawings.

If your lot is in a planned unit development (PUD), which newer subdivisions inside the outer loops often are, the PUD document overrides the base zoning district. You’ll need to read the actual PUD text, usually a 20-to-40-page PDF, to find the accessory structure language. No general guide can shortcut that step.

The Three Documents You Actually Need (And the Order They Come In)

Three approvals gatekeep every ADU in San Antonio: the zoning verification letter, the building permit, and the certificate of occupancy. They arrive in that order, each one unlocks the next, and confusing them causes the most common delay we see in ADU construction in San Antonio.

1. Zoning Verification Letter. This is a written confirmation from Development Services that states your lot’s zoning district, the specific ADU allowances under that district, any floodplain designation, and whether historic review applies. Cost runs between $150 and $400 depending on how you file. Processing takes 10 to 15 business days. You can file this yourself or have your designer or builder file it. Do not skip it. A builder who says “we’ll figure it out during plan review” is betting your permit fee and your schedule on a guess.

2. Building Permit. The building permit application requires full construction drawings, a site plan showing setbacks and impervious cover calculations, structural engineering for your foundation and roof, and energy code compliance documentation. San Antonio Development Services reviews two separate tracks: plans examination for code and zoning compliance, and separate reviews for electrical, plumbing, and mechanical scopes if your ADU has a kitchen or bathroom (nearly all do). Plan review currently runs 4 to 8 weeks for a first pass in San Antonio. If revisions are requested, each resubmittal adds another 2 to 4 weeks. Permits are issued only after every review discipline signs off and the permit fee is paid.

3. Certificate of Occupancy. After the final inspection passes, you apply for the certificate of occupancy, often called the CO. The CO is the legal paper that says the structure can be lived in. Without it, the ADU is not a legal dwelling: insurance claims after a fire or water event become a serious problem, and selling the home with an unpermitted, non-CO’d ADU means significant price concessions or a tear-out. San Antonio issues COs within about 5 to 10 business days after final inspection, assuming no fees or corrections are outstanding.

The order matters. Zoning letter first, because everything else assumes its findings. Then permit, because you cannot legally build or connect utilities without it. Then CO, because the utilities sign off on final connection as part of the occupancy path, not before.

CPS Energy and SAWS: Utility Connections That Run on Their Own Clocks

Here’s where the three-track system bites. You can hold a stamped building permit in your hand and still wait two months to get an ADU energized. CPS Energy and SAWS do not run on Development Services’ schedule, and neither agency cares that your framing crew is standing by.

CPS Energy

If your ADU gets its own meter, you’ll file a service application with CPS Energy. New residential service connections in San Antonio are currently running 6 to 10 weeks from application to meter set for standard overhead-to-overhead service. Underground service, which some newer subdivisions require, runs 8 to 14 weeks. The meter set happens after the electrical rough-in inspection passes, not before, so you need to sequence the CPS application to land roughly when your electrical work is ready. File it too early and CPS tells you to come back; file it too late and a finished ADU sits dark for a month.

If the ADU shares electrical service with the primary home (a subpanel off the main panel), you skip the CPS application entirely. The tradeoff is capacity: the main panel must have enough spare ampacity for the ADU’s loads, and in older San Antonio homes inside Loop 410, many 100-amp panels simply don’t. Upgrading the main panel to 200 amps triggers its own CPS service change application, adding the same 6-to-10-week window and roughly $2,500 to $5,000 in work depending on overhead versus underground.

SAWS

Water and sewer connections run through SAWS. A standard residential tap for a new ADU line runs $2,000 to $4,500 in San Antonio, plus the plumber’s private line work from the tap to the structure. SAWS tap installation currently runs 4 to 8 weeks after approval. If your existing water lateral is undersized for two dwellings on one meter, which is common on older lots in neighborhoods like Alta Vista or Monticello Park, you’ll need a larger meter, which adds SAWS capacity fees that can push the water-side cost past $6,000.

The sequence that works: file CPS and SAWS applications the same week your foundation permit is pulled. That timing puts utility approvals roughly in line with when rough-in inspections will need them. Builders who wait until framing starts are the ones calling utilities every morning hoping for a cancellation.

Historic District Review: What Triggers It and What It Costs in Time

San Antonio has more than two dozen locally designated historic districts: King William, Monte Vista, Lavaca, Dignowity Hill, and others. If your property sits in one, or if it’s individually landmarked, your ADU faces a separate review by the Office of Historic Preservation before Development Services will process the building permit. This applies even to a detached ADU in the backyard, because the designation covers the lot, not just the front-facing house.

Historic review adds 4 to 8 weeks to the front end of any project, and it shapes design in ways you need to accept before hiring a designer. The review looks at height, massing, roof form, materials, window proportion, and visibility from the street. A prefab ADU with a flat metal roof that sails through review in a suburban subdivision like Stone Oak will likely get a correction letter in King William. The historic review standards ask for design that “defers” to the primary structure and the district character. That generally means a gable or hip roof rather than a shed or flat roof, wood or fiber cement siding (James Hardie products are commonly approved), and window sizes that echo the main house rather than a modern two-story glass wall.

The approval path is a Certificate of Appropriateness. Application runs about $300 to $600 in filing fees, and the wait for staff-level review runs 3 to 5 weeks. Projects that require the full Historic and Design Review Commission (HDRC) hearing, which applies when the ADU is visible from the public right-of-way or when the district standards are contested, add another 3 to 4 weeks and a public hearing. We plan for historic review from day one in those neighborhoods, because a denied HDRC petition means returning to the design table, not just paying another fee.

The Inspection Sequence: What Gets Checked and How Long Each Step Takes

San Antonio Development Services inspections run on a scheduled system: you call 2 to 3 days ahead for a window, not a specific appointment time. Each inspection has a code-mandated scope. Here’s what a typical detached ADU sees, in order, with current wait times:

1. Foundation / pre-pour. The inspector checks formwork, rebar placement, and anchor bolt spacing before concrete goes in. This happens 1 to 3 days after you schedule it. Failing this one sets you back a week, so contractors who pour without the green card are both rare and not anyone you want on your lot.
2. Framing. Structural framing, shear walls, roof structure, and hurricane ties get checked against the stamped engineering. Wait time runs 2 to 4 days from scheduling. Wind and hail exposure requirements in San Antonio are real, and inspectors here check them carefully.
3. MEP rough-in. Electrical (with CPS meter pan set and panel in place), plumbing (with SAWS line connected and under slab or in wall), and mechanical (ductwork, if any) are each inspected separately, sometimes on the same day, sometimes across two days. This inspection cannot happen until utilities have done their part. This is the gate that makes CPS and SAWS timing critical.
4. Insulation. Ceiling, wall, and floor insulation R-values get checked against energy code. San Antonio sits in climate zone 2, so R-13 walls and R-38 attic are the baseline, with the 2021 IECC in effect. Prefab units from builders like Boxabl and Plant Prefab typically ship with insulation values that clear these numbers, which shortens this inspection to a photo and a signature.
5. Final building and final MEP. This is the last inspection before the CO. It covers egress, smoke and carbon monoxide alarms, GFCI protection, step and handrail heights, and plumbing fixture operation. Wait time runs 3 to 5 business days. After this passes, you file for the CO.

Total inspection activity across an ADU project in San Antonio typically takes 8 to 12 weeks once construction starts, not counting any correction cycles. A correction cycle, which happens when an inspector finds a code issue, adds 1 to 2 weeks each. The builders with the fewest correction cycles are the ones who walk the job with the code book open before the inspector arrives. That’s the standard Seedling ADU San Antonio holds on every project.

What ADU Permits and Fees Cost in San Antonio in 2026

Nobody wants to discover permit fees mid-project. Here’s an honest line-item picture of what the paper costs on a detached ADU in San Antonio, current as of 2026. These are the city and utility fees, separate from construction cost.

• Zoning verification letter: $150 to $400, depending on filing type and whether historic research is included.
• Building permit fee: San Antonio uses a valuation-based fee schedule. A $150,000 ADU carries a permit fee around $1,800 to $2,600. Smaller 600-square-foot ADUs run $1,200 to $1,800.
• Electrical, plumbing, and mechanical permit fees: typically $300 to $700 combined for an ADU with one bathroom and a kitchen.
• SAWS tap and connection: $2,000 to $4,500 for a standard residential tap, plus capacity fees if a larger meter is needed.
• CPS Energy new service: $500 to $1,500 application and connection fee, depending on overhead versus underground and panel size.
• Historic Certificate of Appropriateness (if applicable): $300 to $600.
• Certificate of Occupancy: usually $100 to $300.

Realistic all-in budgeting for permits and utility fees on a San Antonio ADU: $5,000 to $10,000, with the high end reserved for historic districts, underground utility services, or lots needing drainage mitigation. A written line-item price that breaks these out before work starts is exactly the kind of certainty Seedling ADU San Antonio home puts in front of every family we quote, because surprise fees at the permitting office are the least welcome surprise there is.

Common Mistakes to Avoid

• Running a Google search for “Texas ADU code” and stopping there. State law doesn’t govern your project. The City of San Antonio’s UDC does, and what’s legal in Austin has zero bearing on your lot. Your zoning district and the exact language in Section 35-310 is what matters.
• Designing the ADU before checking the impervious cover math. We see this monthly in established neighborhoods like Jefferson and Woodlawn Lake, where older lots already push 50% or more impervious cover after the driveway and patios. Adding an ADU pushes some lots over the cap, which means a variance you didn’t budget time or money for.
• Applying for a building permit before the zoning verification letter. Development Services will reject a permit application that arrives without a current zoning letter, and you’ll lose your place in the review queue.
• Filing CPS Energy and SAWS applications after framing has already started. That guarantees your project sits unfinished. File both applications the week the foundation passes, and you’ll wait far less.
• Treating historic district review as a formality. In Monte Vista and King William, a Certificate of Appropriateness is a design gate, not a rubber stamp. Budget 4 to 8 weeks and hire a designer who has actually passed that review in the district where you live.
• Skipping the certificate of occupancy to “save time.” There’s no scenario where an unpermitted, non-CO’d ADU is worth it. It hammers home value, voids insurance claims, and turns a $300 paper into a $30,000 problem.
• Hiring a contractor without written permitting and utility line items. If the contract says “permits as needed” or “utilities handled as required,” you’re about to pay for their learning curve. Specific line items, specific fees, specific schedule.

When to Call a Professional

Some San Antonio homeowners file their own zoning verification letter and manage the early paperwork fine. The calculus changes when any of these are true: your lot sits in a historic district, your impervious cover is already within 10% of the cap, you need a panel upgrade for the ADU’s electrical load, or your SAWS lateral is undersized. Any one of those means a coordination puzzle across three agencies that don’t talk to each other. A builder who navigates this weekly, who knows which CPS Energy engineer to call and which SAWS queue moves fastest, saves you the months that stall projects-one reason to weigh DIY vs professional ADU carefully. Seedling’s promise is written pricing before any work starts, including every permit fee, every utility tap, and every inspection cycle, with the 365-Day Done Right Promise behind the finished ADU.

If you’re weighing a garage conversion or a home addition in San Antonio instead of a detached ADU, the permit path differs slightly (conversions frequently carry different zoning requirements), and the right call is a conversation before you commit to drawings. Garage conversion permitting in San Antonio follows its own set of UDC triggers worth understanding early.

Seedling ADU San Antonio offers free estimates in San Antonio – call (210) 981-6358. We’ll walk your lot, pull the zoning and impervious cover numbers, and hand you a written price that includes every fee this guide covers.

Frequently Asked Questions

The Bottom Line

San Antonio ADU permitting is a three-track process run by three different agencies: the city’s UDC for zoning and code, CPS Energy for electrical service, and SAWS for water and sewer. State law won’t help you. Your zoning district sets the height, setbacks, and footprint rules; your utility applications set the schedule; and the certificate of occupancy is the paper that makes the ADU legal to live in. The whole path runs 4 to 8 months from zoning letter to CO, costs $5,000 to $10,000 in permits and fees, and rewards the homeowner who sequences the three tracks deliberately. All of it starts with knowing your lot’s exact numbers, and that’s what a free estimate from Seedling puts in your hand first. For more guides & resources, explore our blog.

Written by Ben Ortega, Owner at Seedling ADU San Antonio, serving San Antonio since 2001.