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

Most San Antonio homeowners start the ADU conversation the same way: they call a general contractor, ask if they’ve “done ADUs before,” and hear yes. Then they sign a contract and discover, six months later, that the builder had never actually pulled an accessory dwelling unit permit in Bexar County, didn’t realize the City of San Antonio caps ADU size at 850 square feet in most residential zones (or 400 square feet in certain historic districts), and never accounted for the separate electrical service tap CPS Energy requires for a second dwelling. This guide and our ADU Permits, Codes & Inspections in TX: What You Need to Know exist because the interview question that actually separates qualified ADU contractors from everyone else isn’t “have you built one?” It’s “pull the permit history for your last three ADU builds in San Antonio and show me the inspection records.” That one question tells you more in five minutes than an hour of references ever will.

Call (210) 981-6358

We’ll walk you through exactly how to run that check, what the five non-negotiable contract clauses are before you sign, how to compare ADU bids apples-to-apples, and which red flags should send you running from a San Antonio ADU estimate. You’ll leave knowing precisely how to vet a builder for an accessory dwelling unit, not a patio cover.

Quick Answer

To hire an ADU contractor in San Antonio, verify the builder’s actual ADU permit history through the city’s public records portal before you interview them, require five specific clauses in writing before any deposit changes hands, and compare bids using a line-item scope that includes utility connections, foundation work, and City of San Antonio inspection fees. A qualified ADU contractor will hand you their permit numbers without hesitation; a remodeler trying to expand into ADUs will deflect, delay, or price the utility work as a “to be determined” allowance. Call (210) 981-6358 for a free estimate from Seedling ADU San Antonio, and we’ll run you through the exact numbers for your lot.

Table of Contents

• How to Verify a Contractor’s ADU Permit History in San Antonio
• The Five Contract Clauses That Must Be in Writing Before You Sign
• Why the Lowest ADU Bid in San Antonio Almost Always Costs More Later
• Questions to Ask a Contractor’s Past ADU Clients (Not Remodel Clients)
• Red Flags Unique to ADU Bids in San Antonio
• The San Antonio ADU Permitting Process, Step by Step
• What an ADU in San Antonio Actually Costs, Line by Line
• Common Mistakes to Avoid

How to Verify a Contractor’s ADU Permit History in San Antonio

San Antonio’s Development Services Department keeps a public records portal that lets anyone search building permits by contractor name, address, or permit number. This is the single most underused tool in ADU hiring, and it’s free. Here’s the step-by-step process:

1. Go to the City of San Antonio Development Services Department online portal and select “Building Permits” search. You don’t need an account to search public records.
2. Search by the contractor’s business name, not their personal name. ADU permits are pulled under the company’s registered contractor license, so a solo operator doing business as “River City Builds LLC” will appear under that entity.
3. Filter for permit type “Accessory Dwelling Unit” or “Residential Addition.” A general remodeler may have 40 permits for kitchen remodels and bathroom remodels. That does not qualify them for an ADU. You’re looking specifically for accessory dwelling unit permits.
4. Open the inspection records for each ADU permit. Look for final inspection approval. A permit that was pulled and then expired or was cancelled tells you the project stalled, possibly because the contractor didn’t know how to frame an ADU to code, failed a rough-in inspection repeatedly, or walked off the job.
5. Cross-check the permit’s build location. Permits in neighborhoods like Alamo Heights, Terrell Hills, Monte Vista, and Mahncke Park tell you the contractor has worked within historic review overlays and stricter aesthetic standards, not just suburban greenfield lots.

In our experience in San Antonio, fewer than one in five contractors who advertise ADU services have more than two completed ADU permits in the city’s system. The rest have addition permits, garage permits, or deck permits. Those are not the same thing. An ADU permit in San Antonio requires the contractor to demonstrate separate egress, independent utility metering or sub-metering, and compliance with the city’s 2018 International Residential Code adoption along with local amendments. The difference matters when your family is living 20 feet from the new structure.

If a builder resists giving you their permit history, that is an answer. A homeowner in Stone Oak recently told us a contractor claimed his permits were “private.” There is no private permit history in San Antonio. The entire record is public by state law.

The Five Contract Clauses That Must Be in Writing Before You Sign

Most ADU problems in San Antonio are not construction problems. They are contract problems. A builder who writes a thorough contract has already thought through the job. A builder who hands you a one-page estimate and asks for a 30% deposit has not. Before any money moves, these five clauses need to be in the document, in plain English:

1. Utility connection scope, itemized. The contract must state exactly who runs the electrical line from the main panel or CPS Energy connection point to the ADU, what size service is being installed (most San Antonio ADUs need a 100-amp subpanel minimum), and whether a separate sewer lateral or a connection to the existing line is planned. “Utilities included” is not a scope. It’s a shrug. ADU builders in San Antonio who write real contracts put utility work on its own line item with its own dollar figure.
2. Change order procedure with a written approval requirement. The contract must say that any price increase or scope change is documented in writing and signed by you before the work proceeds. Verbal change orders are how a $180,000 ADU becomes a $235,000 ADU without anyone noticing until the final invoice.
3. Inspection and permit responsibilities assigned to the contractor. Your contract should state, explicitly, that the contractor pulls all required City of San Antonio permits, schedules all inspections, and is financially responsible for re-inspection fees caused by their own failed work. If the contract is silent on inspections, the failure is on you.
4. Lien release language tied to payment draws. Every payment you make should be conditional on receipt of partial lien releases from the contractor and major subcontractors. In Texas, a subcontractor who isn’t paid can place a lien on your property even if you paid the general contractor in full. The clause protects you from paying twice.
5. Substantial completion and punch list definitions. Define what “done” means. A written punch list process with a reasonable timeline (typically 30 days after substantial completion) keeps the job from ending with a door that doesn’t latch and a contractor who stopped returning calls.

When a contractor resists including any of these clauses, ask them why. The most common answer is some version of “we don’t usually do that.” That’s true. Most contractors don’t. The ones who do are the ones you want for San Antonio ADU work.

Why the Lowest ADU Bid in San Antonio Almost Always Costs More Later

San Antonio’s ADU market is young compared to California or Austin, which means bid disparity is wide; see our ADU Cost Breakdown: The San Antonio Homeowner’s Reference for 2026 for context. In recent months we’ve seen detached one-bedroom ADU estimates in San Antonio range from $165,000 to $310,000 for what looks, at first glance, like the same 600-square-foot structure. A $145,000 gap on the same floor plan is not a margin difference. It’s a scope difference. The lower bid is missing something.

Here’s what the cheap bid usually omits:

• Foundation engineering. San Antonio sits on expansive clay soil. A proper ADU foundation in most of Bexar County requires a soils report and engineered slab or pier design. That single line item runs $8,000 to $18,000. The cheap bid often writes “standard slab” and fails the first inspection.
• Electrical service upgrade. If your main panel is 100 amps or less (common in older homes in Jefferson, Beacon Hill, and Alta Vista), you may need a 200-amp panel upgrade before the ADU can receive power. That’s $4,000 to $7,000 the low bid quietly leaves out.
• Sewer line work. A detached ADU needs either a new sewer lateral tapped to the city main (which requires street cutting and City of San Antonio Public Works permits) or a connection to the existing house’s line. Street taps can exceed $10,000. Omitted from most low bids.
• City permit and impact fees. San Antonio charges building permit fees, plan review fees, and development impact fees for new residential units. On an ADU, total city fees typically run $3,500 to $7,500 depending on size and location. Some builders bury these in “owner will pay” fine print.
• Interior finishes to code. A bathroom that meets San Antonio code with a 30-inch by 48-inch clear shower, proper ventilation, and ADA-adjacent door widths costs more than a remodeler’s “contractor grade” guess.

The right way to compare ADU bids is to create a line-item scope list yourself (shell, foundation, electrical, plumbing, HVAC, insulation, drywall, finishes, permits, site work) and require each bidder to price against it. Then ask every builder who comes in low: “Which of these line items is missing from your number?” Their answer tells you everything.

Questions to Ask a Contractor’s Past ADU Clients (Not Remodel Clients)

References from a kitchen remodel tell you the contractor was polite indoors. References from past ADU clients tell you whether the builder understands what a second dwelling on the property actually involves. When you call a reference, skip the small talk and ask these seven questions:

1. “Did the builder pull the ADU permit themselves, or did you have to?” If a homeowner says they pulled the permit as “owner-builder,” the contractor was not qualified to pull it. That is a massive red flag for a hired professional.
2. “How many change orders did you get, and what was the total dollar increase above the original contract?” A well-run ADU should stay within 5% of contract. Over 15% means the builder bid wrong or manipulated the number.
3. “Did the utility connections (electric, water, sewer) work the first week, or was there a follow-up period after move-in?” Utility failures are the most common ADU defect. If the reference says “we had electric issues for two months,” walk.
4. “How many times did a city inspector fail the job before passing?” One or two failures on a complex ADU is normal. Eight failures is a builder learning on your dime.
5. “Was the crew inside your main house during the build, and if so, how did they handle cleanup daily?” ADU construction means crews moving through your yard and sometimes your home for utilities access. Ask how floors were protected. At Seedling, every crew member follows our Cedarwell Care Promise: shoe covers and drop cloths inside the home, pet-safe products where there’s a choice, and a photo of the cleanup sent to the homeowner before the crew leaves each day.
6. “Did the builder use prefab components or site-build everything?” Prefab ADUs from companies like Boxabl, Plant Prefab, or Mighty Buildings arrive as manufactured modules and get assembled on your foundation. Site-built ADUs are framed on-location. Each route has different timelines and inspection profiles. The reference’s answer tells you what to expect.
7. “If you had one complaint about the builder, what would it be?” Every builder has a complaint. The specific complaint reveals the builder’s character. “They were a week late” is fine. “They stopped returning calls when the punch list came due” is not.

One more thing: ask for ADU references specifically from the last 18 months. San Antonio’s ADU regulations have shifted, and a builder who did great work in 2019 may not be current on the city’s newest overlay district changes.

Red Flags Unique to ADU Bids in San Antonio

Certain problems show up in ADU estimates with predictability. These are the five most damaging ones we see in San Antonio, and none of them are obvious unless you know what to look for:

• Missing utility connection costs. If the bid has a line for “rough-in” but no line for “electrical service upgrade” or “sewer connection to city main,” the price is incomplete. Ask directly: “Is my existing panel sized for this ADU, and does this bid include any panel work?”
• Vague allowance line items. “Allowance for finishes: $15,000” without a defined material list is a way for the builder to lock in a low number and charge extra later. A real finish schedule names specific products: LVP flooring at $4.50 per square foot, Kohler fixtures, 9-foot ceilings with R-38 insulation.
• No mention of City of San Antonio inspections. A bid that lists permits but not inspection coordination means the builder plans to skip inspections until caught. In San Antonio, ADUs require inspections at foundation, framing, rough electrical, rough plumbing, insulation, and final. Each one must be scheduled through Development Services.
• “Turnkey” pricing without site evaluation. No legitimate ADU builder prices a turnkey detached unit without visiting the lot and evaluating access, soil, tree locations, and utility runs. A builder who quotes “starting at $169,000” without walking your property is pricing a generic box, not your home.
• Pressure to sign before a soils report or survey. In San Antonio’s expansive clay zones, a builder who wants a deposit before a geotechnical report is either inexperienced or planning to pass foundation risk onto you later. The survey and soils work should be the first thing contracted, not the last.

The San Antonio ADU Permitting Process, Step by Step

Understanding what the contractor is supposed to be doing helps you evaluate whether they’re doing it. Here’s the actual process for a detached ADU in a standard San Antonio single-family residential zone:

1. Zoning verification. The contractor checks your property against the City of San Antonio’s zoning map and overlay districts. Some neighborhoods, particularly in the historic districts around Monte Vista and King William, have additional board review requirements. Your lot must be in a zone that allows accessory dwelling units by right or with a variance.
2. Site survey and soils report. A licensed surveyor marks property lines and easements. A geotechnical engineer tests the soil. These two documents inform the foundation design and setback compliance (typically 5 feet from rear and side property lines for a detached ADU in standard zones).
3. Architectural and structural drawings. Plans are drawn to San Antonio’s adopted building codes with current wind load requirements (important in our storm-prone region) and energy code compliance (the 2018 IECC applies).
4. Plan submittal to Development Services Department. The contractor submits plans electronically, pays plan review fees, and responds to any review comments. Typical plan review in San Antonio runs 2 to 6 weeks depending on city volume.
5. Permit issuance. Once plans are approved and fees are paid, the city issues the building permit. Construction cannot legally begin before this point.
6. Scheduled inspections at every phase. Foundation, framing, rough electrical, rough plumbing, insulation, and final. The contractor schedules each inspection, the city inspector visits, and the contractor corrects any issues noted.
7. Certificate of Occupancy. After final inspection passes and CPS Energy has connected or confirmed power, the city issues a certificate of occupancy. This is the legal document that makes the ADU livable. You cannot legally rent or sleep in the unit before this is issued.

For homeowners considering a prefab route, companies like Mighty Buildings and Plant Prefab deliver factory-built modules that are assembled and finished on your San Antonio foundation. The permitting path is similar, but plan review often moves faster because the module designs are pre-engineered. Tuff Shed and Boxabl offer additional prefab options at different price points. The important thing is that your contractor knows how to coordinate whichever route you choose with the city’s requirements; for ongoing maintenance planning, read our Seasonal ADU Care for San Antonio: Year-Round Homeowner’s Guide. We work with several of these brands regularly and can walk you through the trade-offs on your specific lot.

What an ADU in San Antonio Actually Costs, Line by Line

Here’s a realistic breakdown for a 600-square-foot one-bedroom, one-bathroom detached ADU in San Antonio, based on current local pricing. These are contractor costs including materials, labor, and overhead:

• Design, survey, and engineering: $12,000 to $25,000
• Foundation (engineered slab on expansive soil): $12,000 to $20,000
• Framing and shell: $45,000 to $70,000
• Electrical (including subpanel and service work): $10,000 to $18,000
• Plumbing (including sewer connection): $8,000 to $16,000
• HVAC (mini-split system is standard for ADUs): $5,000 to $9,000
• Insulation and drywall: $7,000 to $12,000
• Interior finishes (flooring, fixtures, paint, trim): $25,000 to $45,000
• City of San Antonio permit and impact fees: $3,500 to $7,500
• Site work, landscaping repair, final cleanup: $4,000 to $10,000

Total realistic range: $165,000 to $282,000 for a site-built detached ADU. Prefab options can land on the lower end of that range or slightly below depending on the brand and site conditions, but foundation, utility, and permit costs remain the same. Anyone quoting under $150,000 for a complete permitted ADU in San Antonio is cutting scope somewhere. Ask where.

When you call Seedling ADU San Antonio, we’ll walk you through a written line-item price before any work starts. No allowances that balloon later. No “we’ll figure out utilities when we get there.” The price is the price, in writing, on day one.

Common Mistakes to Avoid

• Hiring a remodeler because they did your friend’s kitchen. A kitchen remodel and an accessory dwelling unit share a nail gun and little else. ADUs have separate utility requirements, different permitting path, and stricter foundation engineering in San Antonio’s clay soil. Home addition contractors in San Antonio are closer in skill set, but even then you want specific ADU permit history.
• Comparing bids without a shared scope list. Three different bids on three different scopes tell you nothing. Build your own line-item template and make every bidder price against it.
• Paying a deposit before seeing a survey and soils report. The first money out of your pocket should be for the site evaluation, not the builder’s “mobilization fee.” If the builder collects 20% before doing any site work, you’ve already lost leverage.
• Assuming a garage conversion is cheaper and easier than a detached ADU. San Antonio garage conversions often require structural upgrades to meet living space code, particularly the foundation and roof. The savings are real but smaller than most homeowners expect, and the permitting quirks can be more complicated, not less. Our garage conversion guide for San Antonio covers the specifics.
• Skipping the “who schedules inspections” question. Some builders expect the homeowner to call for inspections. That’s a contractor delegating their core responsibility. The permit is in the contractor’s name; the inspections are their job.
• Neglecting the 365-day service conversation. ADUs settle, shift, and reveal small defects in the first year: a door that starts sticking, a mini-split line that needs adjustment, a window seal that fails. Ask every builder: “What does your first-year service coverage look like, and is it in writing?” At Seedling, every ADU, garage conversion, and home addition carries our 365-Day Done Right Promise: if it’s not done right, we make it right. In writing, every time.

When to Call a Professional

If you’re reading this and wondering whether you can manage an ADU build yourself as an owner-builder, the honest answer for most people is no. Owner-builder projects in San Antonio can work for simple structures, but an ADU is not simple. It involves foundation engineering on challenging soil, separate utility infrastructure, and a permitting sequence that punishes inexperience with weeks of delay. If your lot has any of these complications: expansive clay soil, a sewer line that runs under the proposed ADU site, a main electrical panel under 150 amps, a historic district overlay, or trees protected by city ordinance, get professional help before you spend any money on plans. Seedling ADU San Antonio offers free estimates on ADU projects throughout the San Antonio area. Call (210) 981-6358 and we’ll walk your property, review your lot’s specifics, and give you a written price before any work begins.

Frequently Asked Questions