How to Hire a ADU Contractor in San Antonio: A Step-by-Step Guide

How to Hire a ADU Contractor in San Antonio: A Step-by-Step Guide

A San Antonio homeowner recently lost $34,000 to a contractor who held a valid Texas residential license but had never pulled a detached-structure permit. The project sat untouched for eight months before the city issued a stop-work order. The license check everyone tells you to do would not have caught it. That’s because hiring an ADU contractor is not the same process as hiring a general remodeler. ADUs are detached or attached accessory dwelling units with their own permitting path, utility sequencing rules, and prefab coordination requirements that most residential builders in San Antonio never touch. This guide walks through the exact vetting questions, contract checklists, and red flags that separate an ADU specialist from a remodeler who says “sure, we can do that,” and points you to more guides & resources for every stage of your project.

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Quick Answer

Hiring an ADU contractor in San Antonio requires verifying Texas Department of Licensing and Regulation (TDLR) credentials, confirming detached-structure permit experience, and getting a written line-item price before any money changes hands. The process takes about two weeks of due diligence and saves homeowners an average of $25,000 to $40,000 in avoided change orders, stop-work orders, and remediation work. Skip the verbal estimate entirely: in Texas, a verbal ballpark is not a contract, and a written price is the only thing that holds up when your project stalls.

Table of Contents

• Step 1: Verify the TDLR License and Bexar County Registration
• Step 2: Ask Five Interview Questions That Expose Permit Gaps
• Step 3: Read Every Line of the Bid – Six Items That Should Be There
• Step 4: Demand a Written-Price Guarantee in the Contract
• Step 5: Understand Your Prefab vs. Site-Built Options
• Step 6: Watch for Communication Red Flags During Bidding
• Step 7: The Final Contract Checklist Before You Sign

Step 1: Verify the TDLR License and Bexar County Registration

Every legitimate ADU contractor in San Antonio needs a current TDLR residential builder registration. General contracting in Texas doesn’t require a state license the way it does in California or Florida, but residential construction does fall under TDLR oversight for specific trades, and Bexar County requires registered contractors for permitted work. The key distinction: an ADU is classified as a detached accessory structure, which has a different permit classification than an attached addition or interior remodel. A contractor who has only ever pulled room addition permits (attached, same foundation, same utility panel) may genuinely not know the sequence for a detached structure with its own electrical service, sewer lateral, and foundation inspection hold points.

Here’s the five-minute verification process:

1. Search the TDLR license database: Go to the TDLR website and enter the contractor’s name or business name. Check that the registration is active, not expired, and matches the name on the bid. Discrepancies between the bid name and the registered entity name are an immediate red flag.
2. Check Bexar County’s contractor registration: The county maintains its own registry for contractors pulling permits in unincorporated areas and some municipalities. Ask for the contractor’s county registration number and confirm it online.
3. Ask for three detached-structure permit numbers: Any contractor claiming ADU experience should be able to provide the permit numbers of three completed ADU projects in San Antonio or Bexar County. You can verify these with the city’s Development Services Department. If they hesitate, that’s information.
4. Confirm insurance coverage for detached structures: Ask for a certificate of insurance (COI) naming you as additionally insured. The policy should show general liability coverage of at least $1 million and workers’ compensation if the crew is not all 1099 subcontractors.
5. Search for open complaints: Check the Better Business Bureau and the Texas Attorney General’s consumer complaint database. A clean record isn’t proof of competence, but open complaints about unfinished work or unpermitted construction are disqualifying.

At Benson ADU Builders, we tell every prospective client to run this exact process on us. Transparency is the only sustainable business model in ADU construction, and a contractor who bristles at a license check is telling you something about how they’ll handle the permit phase. For more on how we approach ADU construction in San Antonio, see our ADU Builders in San Antonio page.

Step 2: Ask Five Interview Questions That Expose Permit Gaps

The difference between a remodeler who “can do ADUs” and a genuine ADU contractor shows up in three minutes of conversation. Ask these five questions in the first meeting. The right answers are specific. Vague answers are your signal to move on.

Question 1: “What’s the setback requirement for a detached ADU in San Antonio, and how does it change for a corner lot?”

A competent ADU contractor answers with numbers immediately: San Antonio’s unified development code generally requires a minimum rear setback of 5 feet and side setbacks of 5 feet for detached accessory structures, but corner lots and lots within overlay districts get more complicated. A contractor who says “we’ll check with the city” before giving you any number has likely never pulled a detached structure permit. They should be able to discuss how setbacks shift based on your zoning district (R-4, R-5, R-6) and whether your lot is in a historic district or a Neighborhood Conservation District.

Question 2: “Walk me through the utility stub-out sequence you use.”

This is the single most revealing question. ADUs need their own water service lateral, sewer lateral, and electrical service, and the sequence matters enormously. The correct order in San Antonio: trench and lay sewer lateral first (it’s deepest), then water line, then electrical conduit, all before foundation inspection. A contractor who says “we’ll figure that out during construction” is describing a future stop-work order. A specific answer with depths (sewer laterals in San Antonio typically run 12 to 18 inches below grade per local code) tells you they’ve done this before, and you can cross-check their knowledge against our ADU Builders Maintenance Checklist for San Antonio Homeowners.

Question 3: “Have you ever built with a prefab ADU panel system?”

If the answer is no, that’s not automatically disqualifying for a site-built ADU, but it does tell you they’re not current with the market. Prefab ADUs from companies like Mighty Buildings and Boxabl now account for a growing share of San Antonio ADU permits because they cut construction time by 30 to 50 percent. A contractor who looks confused when you mention prefab panel coordination hasn’t been asked to build one, which means they haven’t done much ADU work recently. We build with Mighty Buildings, Boxabl, and Tuff Shed systems regularly, and the coordination difference is significant: prefab requires a level foundation pad with tight tolerances, crane or forklift staging plans, and factory-to-site inspection documentation that site-built ADUs don’t generate.

Question 4: “What’s your approach to foundation inspection hold points?”

San Antonio’s expansive clay soils shift dramatically with moisture, and the city requires foundation inspections at specific stages: formwork before pour, rebar placement before pour, and post-cure slab flatness. A contractor should be able to name those hold points without thinking. If they wave a hand and say “the city does all that,” run. Foundation failures on ADUs in San Antonio are almost always traceable to skipped inspections or concrete poured without proper rebar clearance. The right answer includes slab edge insulation requirements (now standard in San Antonio’s energy code) and vapor barrier placement.

Question 5: “Can I call two of your past ADU clients?”

A genuine ADU contractor has clients who will take their call. Ask for two references from completed ADU projects, not room additions or kitchen remodels. Call them and ask four questions: Did the permit process go as described? Were there any change orders, and what caused them? Would you hire them again for another ADU? What would you do differently? The last question is the most informative.

We’ve asked these same questions of our own subs for years, and we recommend homeowners use them without apology. The contractor who answers well has nothing to hide.

Step 3: Read Every Line of the Bid – Six Items That Should Be There

Most San Antonio ADU bids are missing the same six line items. They’re not omissions by accident – they’re omissions by strategy, because each missing item becomes a change order three months into the project when the homeowner has no leverage. Here’s what a complete ADU bid must include, line by line.

The six line items most San Antonio ADU bids omit:

• Utility trenching and backfill: Trenching from the main house to the ADU for sewer, water, and electrical typically runs 20 to 60 linear feet depending on lot configuration. In San Antonio’s rocky limestone and caliche soil, trenching costs $18 to $35 per linear foot, and it’s often the single largest un-bid item. If the bid doesn’t show trenching as a separate line item with a per-foot price, ask where it is.
• Foundation engineering and soil report: A detached ADU needs a foundation designed for San Antonio’s expansive clay. The geotechnical soil report runs $1,200 to $2,500, and the structural engineering stamp adds another $800 to $1,800 depending on the foundation type. Slab-on-grade is cheaper to build than pier and beam, but if your lot has a significant slope or reactive soil, pier and beam may be required regardless of what the bid assumes.
• Permit fees and plan review costs: San Antonio Development Services charges permit fees based on project valuation, and for a typical ADU running $150,000 to $250,000, permit fees alone run $2,500 to $4,500. Plan review fees, impact fees, and any historic district review (if applicable) add more. Bids often bury these or exclude them entirely with a footnote that reads “owner responsible for permits.” That’s a load shift, not a favor.
• Electrical service upgrade: A detached ADU needs its own meter or a sub-panel fed from the main house. If your existing panel is 100 amps, you may need a 200-amp service upgrade at $3,000 to $6,000. Many bids show the sub-panel and wiring but quietly omit the service upgrade, which the homeowner discovers during rough-in inspection when the inspector flags the undersized service.
• Drainage and site grading: San Antonio’s flash floods are a design constraint for any detached structure. Proper site grading and drainage (swales, French drains, or a dry creek bed) add $2,000 to $8,000 depending on lot slope and soil permeability. If your bid has no drainage line item, you should assume grading is excluded, which means your ADU may sit in a puddle after the first gully washer.
• Interior finish allowances: Many bids show a single line for “interior finishes” with no dollar breakdown. That’s a placeholder, not a price. Real ADU bids specify flooring material and cost per square foot, cabinet grade and count, countertop material, fixture allowances for the kitchen and bath, and lighting package. If it’s not itemized, it’s not priced.

We’ve reviewed hundreds of bids from San Antonio contractors over the years, and the missing-line-item pattern is remarkably consistent. For more context on how our pricing works, see our Home Addition Contractor in San Antonio page or the Benson ADU San Antonio home page.

Step 4: Demand a Written-Price Guarantee in the Contract

In Texas, a verbal estimate is not binding. Not partially binding, not sort of binding – it is not a contract. The Texas Business and Commerce Code requires construction contracts for residential work over a certain threshold to be in writing to be enforceable. And even a written estimate is not a guarantee unless it contains specific language committing the contractor to the price. Here’s what a written-price guarantee should legally contain.

Elements of a valid written-price guarantee:

• A fixed total price stated in dollars and cents: Not a range, not a “budget,” not an “estimate subject to change.” A fixed price.
• A scope-of-work description with enough detail that an inspector could check it: Every room, every fixture, every material grade. If the scope says “kitchen in ADU,” that’s not a scope. If it says “kitchen with 10-foot run of shaker cabinets in maple, quartz countertop, Kohler fixtures or equivalent,” that’s a scope.
• An explicit statement that change orders require the homeowner’s written signature before work proceeds: This is the single most important sentence in any ADU contract. Without it, verbal change orders become “you agreed to this over the phone” disputes, and in Texas those disputes are hard to resolve without litigation.
• A defined process for allowances: If finishes are priced as allowances, the contract should say how overages are calculated, who bears the risk of price increases during construction, and when allowance items are locked (usually before drywall).
• A defined remedies clause: What happens if the contractor is late? What happens if the work fails inspection? A written guarantee is worthless without a remedy, and a remedy without a timeline is also worthless. The remedy should include specific dates, specific responsibilities, and a clear escalation path.

At Benson ADU Builders, every project gets a written price before any work starts, and that price is governed by The Relay Visibility Guarantee: a 365-Day Done Right Promise on every project, a written guarantee stamped on the paperwork, and a free second visit if any covered repair fails. That’s not marketing language – it’s contract language. If a contractor won’t put their promises in the contract, the promises don’t exist.

Step 5: Understand Your Prefab vs. Site-Built Options

One of the biggest decisions San Antonio homeowners face is whether to build a site-built ADU or go with a prefab system. Both have legitimate places in the market, but the decision affects your timeline, your budget, and your contractor options. Understanding the tradeoffs will save you from paying a premium for the wrong approach.

Site-built ADUs:

A site-built ADU is constructed entirely on your property, stick by stick. This is the traditional approach and it’s what most San Antonio contractors are comfortable with. Site-built gives you complete design flexibility and works well for odd-shaped lots, tight setbacks, or custom aesthetic requirements. The downside: site-built ADUs in San Antonio typically take 8 to 14 months from permit to certificate of occupancy, and every day of that timeline is a day you’re paying carrying costs or losing rental income. Site-built costs in San Antonio currently run $250 to $400 per square foot for a finished ADU, depending on finishes and site conditions.

Prefab ADUs:

Prefab systems like Mighty Buildings, Boxabl, and Plant Prefab build the ADU in a factory and ship it to your site for assembly. The advantages are significant: construction timelines compress to 4 to 7 months from permit to occupancy, factory quality control is generally tighter than field construction, and the price is locked before the factory starts cutting steel or panels. Boxabl units, for example, ship as foldable modules that unfold on-site in under a day, which is dramatically faster than site-built framing. Mighty Buildings uses 3D-printed composite panels with higher insulation values than typical San Antonio code requires. Tuff Shed offers a different segment entirely: finished backyard structures that work well as studios or offices but require less permitting for certain uses.

Not every prefab system works for every lot. Prefab requires crane access or a flat staging path, and San Antonio lots with mature oak trees or steep driveways may not accommodate some modules. A contractor who builds with both prefab and site-built methods can help you evaluate which path fits your lot, your timeline, and your budget – instead of steering you to whichever one they happen to know how to build. We’re authorized to build with Mighty Buildings, Boxabl, and Tuff Shed systems alongside our site-built work, which gives you a genuine comparison instead of a take-it-or-leave-it product.

Step 6: Watch for Communication Red Flags During Bidding

How a contractor communicates during the bid phase predicts how they’ll communicate during construction with surprising accuracy. Here are the five red flags we tell homeowners to watch for, based on what we hear from clients who’ve been burned before they found us.

Red flag 1: The bid takes more than two weeks.

A licensed, experienced ADU contractor can produce a written line-item bid within 14 days of a site visit. If it takes longer, it’s usually because the contractor is not pricing your project themselves – they’re waiting on subs, or shopping for the cheapest suppliers, or they’ve put your project in a queue behind more attractive work. None of those are signs of a contractor who respects your schedule.

Red flag 2: They won’t put numbers in writing before the first meeting.

Some contractors insist on multiple in-person meetings before they’ll discuss any dollar figures. This is a sales technique, not a technical requirement. A contractor with ADU experience can give you a ballpark range on the first call based on square footage and site address. If they refuse, they’re controlling information, not providing expertise.

Red flag 3: You can’t reach a live person.

Call the contractor’s office on a Saturday afternoon and see what happens. If you get a voicemail loop, that’s what you’ll get when your foundation inspector needs a document on a Friday and the pour is scheduled for Monday. We keep a live person on the phone 24/7, every day of the year. It’s a simple operational choice that signals how serious we are about responsiveness.

Red flag 4: They use vague scope language.

Watch for phrases like “as needed,” “as required,” “standard installation,” “typical finishes,” and “per plan.” These are all placeholders for future change orders. A real bid uses specific material names, quantities, dimensions, and installation methods. If you can’t picture the finished ADU from the bid language, the bid isn’t done.

Red flag 5: They push a single approach without discussing alternatives.

A contractor who only offers site-built construction and dismisses prefab without specific reasons (lot constraints, crane access) may be protecting their own comfort level at your expense. The best ADU contractors in San Antonio can discuss both paths and give you a real comparison.

Step 7: The Final Contract Checklist Before You Sign

After all the interviews and bid reviews, you’re down to one contractor and one contract. Here’s the final checklist before you sign anything. If any item on this list is missing, the contract is not ready.

1. Fixed total price in writing, with no escalation clauses tied to material prices. Material price escalation has become common in recent years, but a contractor’s bid should hold for at least 30 days after signing, and ideally for the duration of the project unless you change the scope.
2. Payment schedule tied to completed milestones, not calendar dates. Typical structure: 10% at contract signing, 30% at foundation completion, 30% at rough-in completion, 20% at drywall completion, 10% at final inspection. Never pay more than 10% upfront. Contractors who demand 30-50% upfront are financing their own cash flow problems with your money.
3. Lien waiver language from every subcontractor and supplier. If a sub doesn’t get paid, they can file a mechanic’s lien against your property even if you already paid the general contractor. Your contract should require lien waivers from every sub and supplier before each progress payment.
4. Insurance certificates naming you as additionally insured. The COI should come directly from the insurance agent, not from the contractor, and it should be current. Verify it by calling the agent.
5. Written change order process with your signature required for any cost change. This is non-negotiable. Any change order without your written approval is not your responsibility.
6. Permit responsibility clearly assigned to the contractor. The contract should state that the contractor is responsible for pulling all permits, scheduling all inspections, and resolving any permit violations. If the contract says “owner responsible for permits,” walk away.
7. Completion date with a defined remedy for delay. A completion date without a penalty for delay is a suggestion, not a commitment. The remedy should be specific (e.g., $100 per day after the completion date for every day of delay not caused by weather or owner changes).
8. The warranty in writing, with a defined term and defined scope. Our warranty is the 365-Day Done Right Promise: if anything isn’t right within a year, we make it right, in writing, on every project. If your contractor’s warranty is verbal, it doesn’t exist.

Common Mistakes to Avoid

• Hiring a room addition contractor to build a detached ADU. Room additions attach to the existing structure and share utilities. Detached ADUs have their own foundation, their own utility laterals, and a different permit path. The skills don’t automatically transfer, and the $34,000 stop-work order in our opening example came from exactly this false assumption. If the contractor hasn’t pulled detached-structure permits in San Antonio, keep looking. See our Room Addition Contractor in San Antonio page to understand the difference.
• Signing a contract with vague scope language. “As needed” and “per plan” are not scope descriptions. They’re placeholders for change orders. Every line item should be specific enough that an inspector could verify it.
• Paying more than 10% upfront. No legitimate ADU contractor needs more than 10% to start. More than that and you’re financing their overhead with your savings.
• Skipping the reference calls because the contractor “seems great.” Everyone seems great in sales mode. Past clients will tell you what the bid phase looked like compared to the construction phase. Make the calls.
• Assuming the permit process is the contractor’s problem once you sign. It is their responsibility to pull permits, but it’s your responsibility to verify they did before construction starts. Ask for the permit number and confirm it with San Antonio Development Services. A contractor who starts work without a permit exposes you to fines, stop-work orders, and a host of headaches.
• Buying on price alone. The cheapest ADU bid in San Antonio is usually the one missing the most line items. When the change orders start arriving, the cheap bid becomes the most expensive one. Compare scope first, price second.
• Not checking the foundation design for expansive clay soil. San Antonio’s clay soils expand and contract with moisture, and a foundation designed for a different soil type will crack. Your bid should include a geotechnical report and a foundation designed for your specific lot, not a generic slab.

When to Call a Professional

Some parts of the ADU process are genuinely DIY-able: researching zoning, comparing prefab brands online, and reading San Antonio’s unified development code are all within reach of a motivated homeowner. Other parts are not. Foundation design for expansive clay soil requires a structural engineer and a geotechnical report. Electrical service upgrades require a licensed electrician and coordination with CPS Energy. Sewer lateral connections require a plumbing permit and inspection coordination with SAWS. If you’re uncertain about any of these items in your bid, call a professional before you sign. Benson ADU San Antonio offers free written estimates in San Antonio and we walk every potential client through the scope line by line. Call (430) 258-2928 to schedule yours.

The Bottom Line

Hiring an ADU contractor in San Antonio is a process of elimination, not a leap of faith. Verify the TDLR registration and Bexar County credentials. Ask the five interview questions that separate ADU specialists from remodelers. Read every line of the bid and demand the six items most bids omit. Get the written-price guarantee into the contract with specific remedy language. And watch for the communication patterns during bidding that predict problems during construction. The homeowners who do this work upfront rarely lose money. The ones who skip it sometimes lose $34,000. Choose your path accordingly.

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