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

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

The single most common reason San Antonio ADU permits are rejected on first submission isn’t a zoning violation. It’s a site plan that shows the wrong impervious cover calculation, a math error any homeowner can learn to check in about ten minutes. We’ve seen it happen dozens of times across Bexar County, from Terrell Hills to Helotes, and every rejection costs the homeowner three to six weeks in resubmission time before a single footing gets poured. This guide walks through the actual permit workflow, the inspection sequence, the utility hookup thresholds, and the paperwork details that most The Complete Guide to ADU in San Antonio skip, so you can file once and move on to construction.

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Quick Answer

ADU permits in San Antonio go through the city’s Development Services Department, and the process typically takes 4 to 8 weeks for plan review on a detached unit, with fees ranging from roughly $1,200 to $3,500 depending on size and utility work. You’ll need a full application packet that includes a site plan with accurate impervious cover math, construction drawings, and utility documentation before the city will even accept your file. After approval, expect four inspections before you can legally move anyone into the unit.

Table of Contents

• How ADU Permits Actually Work in San Antonio
• Impervious Cover: The Math That Kills Permits
• The Exact ADU Application Packet San Antonio Requires
• The Four-Inspection Sequence for a Detached ADU in Bexar County
• CPS Energy and SAWS Utility Requirements for ADUs
• How Prefab ADUs Navigate San Antonio Plan Review Differently
• What ADU Permits Cost and How Long They Take in San Antonio
• Common Mistakes to Avoid
• When to Call a Professional
• Frequently Asked Questions
• The Bottom Line

How ADU Permits Actually Work in San Antonio

Texas has no statewide ADU code. The state legislature has kicked around the idea of a uniform accessory dwelling unit statute for years, but as of this writing, every municipality writes its own rules. That means a permit that sailed through Austin’s ADU-friendly overlay districts can be rejected in San Antonio for reasons that seem arbitrary until you understand the city’s specific Unified Development Code chapters. San Antonio’s UDC Chapter 35 governs accessory dwelling units, and it’s not a short read.

The city defines an ADU as a secondary dwelling unit on the same lot as a primary single-family home, with its own kitchen, bathroom, and sleeping area. It can be attached, detached, or converted from existing space like a garage. In San Antonio, the unit can’t exceed 1,000 square feet of conditioned space, and the lot must be zoned for single-family residential use. Those are the headline rules. The details are where applications die.

Here’s the workflow in order:

1. Zoning verification. You check your property’s zoning district through the city’s online zoning map. If you’re in a historic district or a neighborhood conservation district, additional design review applies before you ever submit.
2. Site plan preparation. This is the document that causes most first-time rejections. More on that below.
3. Application submission. You file through the city’s online portal or in person at the Development Services Department on South Frio Street.
4. Plan review. A plan reviewer checks your drawings against the UDC, building code, and fire code. If they find issues, they issue a correction letter and you fix and resubmit.
5. Permit issuance. Once approved, you pay the permit fees and the permit is issued. Construction can begin.
6. Inspections. You call for inspections at each stage, and the city sends an inspector to verify the work matches the approved plans.
7. Certificate of occupancy. After the final inspection passes and utilities are connected, the city issues a certificate of occupancy. Now the unit is legal to live in or rent.

The online portal versus in-person question comes up a lot. The portal is faster for tracking status and resubmitting corrections, but in-person submission at the Development Services Department lets a permit technician do a quick completeness check before you hand over the fee. If you’re confident in your paperwork, file online. If this is your first ADU and you did the drawings yourself, the in-person option can catch a missing form before it costs you three weeks in review queue-something our DIY vs Professional ADU: The San Antonio Homeowner’s Decision Guide covers in more detail.

We build ADUs across San Antonio and the surrounding county, and our team has filed enough of these to know which corrections are routine and which ones signal deeper problems. If you’re working with an ADU builder in San Antonio who files permits regularly, they’ll typically handle the entire workflow from zoning check to final inspection sign-off. If you’re going owner-builder, budget twice as much time for the paperwork as you think you’ll need.

Impervious Cover: The Math That Kills Permits

Impervious cover is the percentage of your lot that water can’t soak through. Rooftops, concrete slabs, driveways, patios, and even compacted gravel in some cases all count. San Antonio residential zones typically cap impervious cover at 45% to 55%, depending on the specific zoning district. Go over that cap and your permit is dead on arrival, no matter how beautiful the ADU design is.

Here’s the part most homeowners miss: a detached ADU adds two things to your impervious cover calculation at once. The building footprint itself, plus any walkway or utility path connecting it to the primary home or alley. A 600-square-foot ADU slab doesn’t just add 600 square feet. It might add 700 or 750 square feet once you include the connecting sidewalk, the pad for the mini-split condenser, and any steps or landings.

The calculation itself is simple:

1. Measure your total lot area from the survey or county appraisal district record.
2. Multiply by your zone’s maximum impervious cover percentage. In an R-6 zone with a 45% cap on a 7,000-square-foot lot, that’s 3,150 square feet of allowable impervious cover.
3. Add up every impervious surface already on the property, including the existing home footprint, driveway, walkways, patio, and any accessory structures.
4. Subtract your existing total from the allowable total. What’s left is your ADU budget.
5. Then factor in the connecting walkway and any platform or pad for mechanical equipment before you finalize the ADU footprint.

We’ve walked lots in Alamo Heights and Castle Hills where the homeowner assumed they had room for a 1,000-square-foot ADU and the math said 500, a classic example of the ADU Warning Signs: A San Antonio Homeowner’s Reference Guide in action. Sometimes the fix is simple, like replacing a concrete walkway with permeable pavers or stepping stones that don’t count toward impervious cover. Other times the solution is a narrower ADU footprint or a different placement on the lot. The point is you want to know the number before you pay an architect or order a prefab unit.

If you’re considering a home addition rather than a detached unit, the math shifts because an attached addition shares a wall with the primary structure and often extends the existing roofline. The impervious cover impact is limited to the new foundation area plus any new walkways, which is typically less than a fully detached ADU. Our home addition contractor team in San Antonio reviews the impervious cover budget on every project before the design phase starts, because it’s cheaper to adjust the design than to resubmit a rejected permit.

The Exact ADU Application Packet San Antonio Requires

The city doesn’t make this list easy to find. The Development Services Department website has the forms, but they’re spread across multiple pages and the application checklist changed a few years ago when the city moved to electronic plan review. Here’s the complete packet as of this writing:

• Building permit application. The core form with property address, legal description, owner information, and contractor information if you’re using one.
• Site plan drawing. To scale, showing the existing home, the proposed ADU, property lines, setbacks from all lot lines, existing and proposed impervious cover with square footage calculations, and the location of any easements. This drawing is where the impervious cover math gets shown, and it’s the document that gets scrutinized hardest.
• Construction drawings. Floor plan, elevations, foundation plan, and a roof plan. These have to be stamped by a Texas-licensed engineer or architect if the ADU exceeds certain structural thresholds, which most detached units on piers or slabs will trigger.
• Energy compliance documentation. San Antonio has adopted energy code requirements that go beyond the state minimum. You’ll need the IECC compliance certificate filled out and signed.
• Tree preservation documentation. San Antonio has a tree ordinance. If your ADU site has protected trees, you’ll need a tree survey and a preservation plan, and sometimes a tree mitigation payment.
• Utility disconnect or tap documentation. Depending on your utilities, this might be a letter from SAWS or CPS Energy confirming service availability, or a planned tap application.
• Contractor registration. If you’re not owner-building, your contractor must be registered with the city and current on their registration fee.

Missing any one of these items means the intake technician sends you home or the online system rejects the upload. We’ve seen homeowners show up with beautiful construction drawings and no site plan, or a site plan with no impervious cover table, and they’re back in the car before they finish their coffee. The packet isn’t complicated, but it is complete, and completeness is the whole game.

The Four-Inspection Sequence for a Detached ADU in Bexar County

Once your permit is issued, the inspection schedule begins. San Antonio’s Development Services Department runs inspections on a next-day or two-day scheduling system, and you request each inspection through the online portal or by phone. Here’s the order and what inspectors actually check:

1. Foundation inspection. This happens after the forms are set and the rebar is tied but before concrete is poured. The inspector checks the footing depth against the approved foundation plan, verifies the rebar spacing and size, and confirms the forms are placed within the approved setbacks. The most common flag at this stage is rebar that’s too close to the edge of the form or missing the required clearance from the dirt. If you pour before this inspection passes, you’re digging it out and starting over, so don’t let a concrete sub talk you into skipping the call.

2. Framing inspection. After the walls are up, the roof is sheathed, and before any insulation goes in. The inspector checks stud spacing, header sizes, hold-down hardware, shear wall nailing patterns, and the roof-to-wall connections. Wind load requirements in Bexar County are real, and a framing inspection fails most often on missing hurricane clips or incorrect nail spacing on shear panels.

3. MEP rough-in inspection. Mechanical, electrical, and plumbing all get checked at the same time in San Antonio. The electrician’s rough work, the mini-split or HVAC lineset, the drain lines, the water supply lines, and the venting all have to be visible and done before insulation and drywall cover them. This is the inspection that gets rescheduled most often because one trade finished but another didn’t, and the inspector won’t do a partial pass. Get all three trades done before you call.

4. Final inspection. After all finishes are in, fixtures are set, and the unit is complete. The inspector walks through checking that everything matches the plans, that required safety features like smoke alarms and GFCI outlets are installed, and that the address is visible. Once this passes and the utility release is confirmed, you get your certificate of occupancy.

Inspectors in San Antonio are thorough, and they don’t give partial credit. If one item fails, the whole inspection fails, and you reschedule and pay a reinspection fee. The fastest path through is having your contractor present at each inspection with the approved plans in hand and a tape measure ready.

CPS Energy and SAWS Utility Requirements for ADUs

A detached ADU in San Antonio typically needs its own electric meter unless the unit is designed as a sub-panel fed from the primary home’s service. CPS Energy’s trigger threshold for a separate meter depends on the projected load of the ADU, and once you cross about 100 amps of calculated demand on a new structure, a separate meter and service drop becomes the practical path. A small studio ADU with a mini-split and an electric water heater might run on a 60-amp sub-panel from the main house, but any unit with a full kitchen, laundry, and central HVAC is looking at a dedicated service.

The important question to ask early is whether your existing transformer and service drop can handle the additional load. In older San Antonio neighborhoods with aging infrastructure, the answer is sometimes no, and the service upgrade becomes a CPS Energy project with its own timeline. That’s a conversation to have during design, not after the walls are up.

SAWS handles water and sewer. A new ADU dwelling unit needs water service, and the options are a separate tap from the main (expensive, and requires a permit and excavation in the street or alley) or a service line branched from the primary home’s supply (cheaper, but it has to meet pressure and sizing requirements). On the sewer side, the ADU’s drain line has to tie into the property’s existing lateral with proper slope and cleanouts. If the existing lateral is old cast iron or in poor condition, SAWS may require replacement to the main. That’s a five-figure surprise if you didn’t plan for it.

These utility conversations are exactly where a written scope and price matters. Our room addition contractor team in San Antonio includes utility work in the written price before construction starts, so homeowners aren’t hit with a CPS Energy or SAWS change order in month three of the build.

How Prefab ADUs Navigate San Antonio Plan Review Differently

Prefab ADUs change the permit math in San Antonio, but not the way most people expect. A panelized unit from Plant Prefab or a modular unit from Boxabl still has to meet the same local building code as a stick-built structure. The difference is in the documentation and the review path.

Factory-built units come with engineering stamped in the factory’s state of origin, and Texas generally accepts those stamps through reciprocity agreements, but San Antonio plan review still wants to see how the unit ties to the foundation system designed for local soil conditions. Bexar County sits on expansive clay soils, and the foundation design here is different from what a factory in California or Arizona assumes. The unit manufacturer has to provide anchor bolt patterns, hold-down locations, and structural connection details that a local engineer then adapts to a San Antonio-appropriate foundation.

The plan review itself is often faster because the factory drawings are consistent and detailed, and the reviewer has seen the same package before if it’s a popular brand. Tuff Shed structures, which some homeowners choose for a small studio-level ADU conversion, go through a different path because the base structure is classified as an accessory building rather than a dwelling unit until the interior systems are added.

The documentation burden shifts rather than disappears. Instead of a local architect stamping a full set of custom drawings, you’re submitting the factory’s engineering package plus a site-specific foundation design plus a local energy compliance certificate. The factory has to provide current engineering stamps, wind load certifications for Texas, and a letter stating the unit meets Texas accessibility provisions if applicable. If the factory has never sold a unit in Bexar County before, plan review staff may ask for additional calculations, and that back-and-forth can eat weeks.

What ADU Permits Cost and How Long They Take in San Antonio

Here are the numbers, as transparently as we can give them:

Timelines are less predictable. A simple garage conversion with no new foundation work and no utility upgrades can clear plan review in 3 to 4 weeks if the drawings are clean. A detached ADU with a new foundation, new sewer connection, and an energy compliance correction letter might take 8 to 12 weeks before the permit is issued. The city’s plan review queue moves at its own pace, and there’s no expedited residential ADU track in San Antonio as of this writing.

What you control is the number of correction cycles. Every correction letter adds two to four weeks to the timeline. A clean first submission is the difference between a spring groundbreaking and a summer groundbreaking. That’s why we document every permit package in writing before submission and track it through the city portal until the permit is in hand. If you want a benchmark, our Benson ADU San Antonio home page has information about our full permit-handling process for ADU projects.

Common Mistakes to Avoid

• Wrong impervious cover math. The site plan shows the ADU footprint but omits the connecting walkway, patio, and mechanical pad. The reviewer’s calculation puts you over the cap, and the permit dies on first review.
• Buildings over the 1,000-square-foot cap. San Antonio’s UDC caps detached ADUs at 1,000 square feet. Design a 1,050-square-foot unit and the permit won’t even get reviewed, it’ll be returned as non-compliant.
• Ignoring the tree ordinance. A protected oak or pecan in the ADU footprint triggers a tree survey and mitigation process that adds weeks and money. Check the tree inventory on your lot before you pick a site.
• Pouring concrete before the foundation inspection. This happens more often than you’d think, usually because the concrete sub is on site and ready to go. The inspector hasn’t signed off, and now you’re demolishing a fresh slab.
• Assuming utility connections are automatic. CPS Energy and SAWS have their own timelines and requirements. Starting construction before confirming that the existing service can handle the ADU load can stop the project at the final inspection.
• Filing owner-builder without a permit history. Owner-builders can absolutely pull permits in San Antonio, but plan review staff will scrutinize the drawings harder if there’s no licensed contractor or engineer in the application. A missing stamp sends you back to square one.
• Not confirming zoning before buying a prefab unit. Some San Antonio neighborhoods with deed restrictions or historic designations prohibit ADUs entirely, regardless of what the city code says. Verify before you order a factory-built unit that can’t be returned.

When to Call a Professional

If your lot has a tree issue, a utility service question, or an impervious cover calculation that comes out anywhere near the cap, call someone who does this every week. The same goes for historic districts, corner lots with unusual setback rules, and any situation where the ADU will share a wall with an existing structure. The permit package is only part of the cost. A rejected first submission costs you time you can’t get back, and San Antonio’s construction season doesn’t wait for paperwork. Benson ADU San Antonio offers free estimates in San Antonio, call (430) 258-2928 to talk through your site with someone who knows the local review process. We’ll tell you honestly whether your project is straightforward or whether you’re in for a longer permit path, and we’ll put the price in writing before anything starts.

Frequently Asked Questions

The Bottom Line

San Antonio ADU permits are not a mystery. They’re a checklist, and the checklist has about seven items that show up on every application, from the site plan with accurate impervious cover math to the energy compliance certificate to the contractor registration. The homeowners who breeze through are the ones who treated the paperwork as part of the project rather than an obstacle to the project. The homeowners who stall out are the ones who guessed at the impervious cover, skipped the tree check, or ordered a prefab unit before confirming zoning. Get the packet complete, file it once, and call for inspections on schedule. That’s the whole system, and now you know it better than most people who submit drawings to the city next week.

Written by Troy Eastman, Owner at Benson ADU San Antonio, serving San Antonio since 2006.