What slab does a metal building in the San Antonio area need?

It is a foundation an engineer designs for your building on your lot. A metal building does not spread its weight along a wall the way a stud-framed one does. Each rigid frame puts its load into two column bases, which press down, shove outward and, in a windstorm, pull up. The concrete handles all three, sized off the manufacturer's reaction sheet, not a rule of thumb.

Inside the City of San Antonio, who draws it is written down. The city commercial project application guide requires every structural sheet, meaning the foundation and the structural framing, to be designed and stamped by a Texas professional engineer, and says trade and civil documents may need engineering too, depending on scope.

Outside a city, the statute sets the minimum. Occupations Code 1001.056 lets a building skip the state engineering chapter when nobody holds out to offer engineering services to the public and the building is one story, 5,000 square feet of floor or less, with no clear span wider than 24 feet across its narrow side. Where a building that size has an unsupported span over 24 feet, the engineering requirement falls only on the roof framing (trusses, beams and other members holding up the roof), which has to be engineered or pre-engineered. A clear-span shop wider than 24 feet falls outside that exemption on the span alone.

Checked at City of San Antonio Development Services, commercial project application guide, 2026-09-13.

Checked at Texas Legislature Online, Occupations Code Chapter 1001, engineers and engineering, 2026-09-13.

The building bolts to it, and the bolts are cast in before the concrete sets. The manufacturer sends an anchor bolt plan fixing where each bolt goes, how far it sticks up, and what load each column base puts into the foundation. Pour before that plan exists and the slab may need drilling, cutting or a second pour.

So the order runs: order the building, get the reaction and anchor bolt drawings, design the foundation to them, then pour. The rest of the job runs the same way, laid out in the start-to-finish San Antonio guide.

It still holds if you already own the steel. An owner who needs erection of a pre-engineered package still gets the foundation designed to that package, since the bolt pattern and reactions shipped with it.

Three different foundation problems lie within an hour of each other here, and the county line gives a rough idea which one you have. From the primary soil and groundwater records, checked 2026-09-13:

• Bexar County. Up north, shallow to very shallow stony soil over hard limestone, the Tarrant soils carrying a few inches to about 10 inches of clayey surface over fractured rock. The east and west uplands are Houston Black-Houston deep clay, about 10 percent of the county, cracking wide as it dries. The south and southwest are sand over clay. Source: USDA Soil Survey of Bexar County, Texas (1966).

• Medina County. The northern hills run shallow: Tarrant cobbly clay about 16 inches thick over fractured limestone, with coarse fragments over 35 to 90 percent of the surface. The south is Rio Grande Plain, and its biggest association, about 30 percent of the county, is deep loamy and clayey calcareous soil. Source: USDA Soil Survey of Medina County, Texas (1977).

• Wilson County. About 35 percent is Wilco-Floresville-Miguel, deep sandy and loamy soil with clayey layers below and slow permeability, and about 20 percent is the Eufaula-Patilo sand belt. For the Elmendorf-Luling-Denhawken association the survey lists shrink-swell potential and corrosivity to uncoated steel pipe. There is no hard limestone shelf under the county. Sources: USDA Soil Survey of Wilson County, Texas (1977), and Texas Board of Water Engineers Bulletin 5710.

• Atascosa County. The biggest unit, about 25 percent, is Amphion-Floresville-Imogene, whose limits the survey lists as shrinking and swelling, corrosivity to uncoated steel, low soil strength and slow permeability. About 17 percent is sandy, the Weigang soils are limited by shallow bedrock, and the Hindes soils formed over caliche beds. Source: USDA Soil Survey of Atascosa County, Texas (1980).

• Guadalupe County. Close to half the county is deep clay: Houston Black-Heiden on the uplands, about 22 percent, rated very high for shrink-swell, and Branyon-Barbarosa-Lewisville at another 23 percent. The biggest association, about 33 percent, is Crockett-Demona-Windthorst, with moderate to high shrink-swell in the lower layers. Source: USDA Soil Survey of Guadalupe County, Texas (1977).

• Karnes County. The northwest half is deep soil with light loamy surfaces over clayey subsoil. The rest has loamy surfaces over reddish clayey subsoil with limestone inside 40 inches of the surface, plus gray to black cracking clays high in shrink-swell. Source: Handbook of Texas Online, Karnes County, an encyclopedia entry, not a primary soil survey.

• Frio County. Flat to gently rolling plains topped with deep to moderately deep light-colored loam, over limestone and calcareous to neutral clayey subsoil. Source: Handbook of Texas Online, Frio County, an encyclopedia entry, not a primary soil survey.

That is the call of the engineer sealing your foundation plan, and no page checked for this site requires a geotechnical report on a metal building. What the records do require is the seal: inside San Antonio the city guide puts the foundation and structural framing sheets under a Texas professional engineer's stamp.

A county soil survey does not replace borings. The surveys above map associations that cover whole percentages of a county, which tells you which of the three problems your part of it tends toward. It does not say how deep the rock sits at the back of your lot, or how far the clay moves through a South Texas summer.

Use the survey as the reason to ask. Ask any contractor bidding the work whether a soil investigation is in scope and who pays, and get it in the written estimate. On a rocky lot in Bexar County, TX, the surprise is excavation. On the deep clay of Guadalupe County, TX, it is the foundation section.

Checked at City of San Antonio Development Services, commercial project application guide, 2026-09-13.

Three shapes cover most of what gets poured, and the engineer chooses by the loads and the soil.

• Monolithic slab with a thickened turndown edge: the floor and the perimeter beam go in one pour, the beam deepened where the frame columns sit.

• Slab on separate footings or drilled piers: the column bases get their own footings or piers taken down to bearing, and the floor is poured around them. Common where column loads run high, the bearing layer is deep, or the surface clay moves.

• Post-frame foundation: posts go into the ground, and the floor is a separate pour or not concrete at all. That is a different structure from a bolted steel frame, covered under post-frame and pole barn buildings.

Square, level, cured, in the right spot, and reachable. The anchor bolts have to sit in the pattern, at the projection, the plan calls for, because the base plates are punched to match and a misplaced bolt gets fixed with a drill and an engineer. The diagonals of the pour must match or the frames will not line up.

Access counts as much as the concrete. A crane and a steel truck both have to reach the pad and stand somewhere while the frames go up, on ground that will hold them. Finished grade belongs on the drawing, not settled in the field. The dirt work behind both is on the pad and site prep sheet, planned with the slab, not after it.

Inside a city, it gets inspected under the building permit. Outside, it turns on the county, and two of the seven post a foundation permit by name with a price.

Inside the City of San Antonio a commercial job moves through zoning, plan intake, plan review, permit, inspections, utility release and certificate of occupancy at Development Services, so the foundation gets inspected inside that run. The city fee schedule also lists a flat $184.00 for repairing an existing foundation among miscellaneous residential projects, while new residential construction is priced by square footage.

A Texas county cannot run that kind of review. Local Government Code Chapter 233 leaves a county without power to adopt a general commercial building code, or a structural, mechanical, plumbing or electrical code, for the unincorporated area, and the one power in that chapter that reaches a commercial building is the fire code permit. The statute names a foundation inspection in only one place, the county residential code in Subchapter F: it applies only where a county has adopted a resolution or order requiring it, covers a single-family house or duplex rather than a commercial building, and has the builder contract three private inspections, the foundation one before concrete is placed. No county permit stack on this site records such an adoption.

What each county posts about the foundation stage, checked at its own site 2026-09-13:

• Bexar County. The Fire Marshal fee schedule, dated January 1, 2024, lists a $500.00 foundation permit, and the building permit fee covers at least three construction site visits. Fire Marshal's Office, 210-335-0300.

• Guadalupe County. The Fire Marshal fee schedule, effective February 1, 2026, sets a $500.00 site preparation and foundation permit, covers at least three site visits in the building permit fee, and charges $125.00 for final inspection with certificate of compliance. Fire Marshal Office, 830-303-8856.

• Atascosa County. A building permit is required before a new commercial or public building goes up in the unincorporated area, the Fire Marshal may not issue it until the plans are reviewed, and it covers at least three site visits, ending with a Request for Final Inspection and a Certificate of Compliance. The fee schedule has no separate foundation permit. Fire Marshal and Emergency Management Office, 830-769-2029.

• Wilson County. The county development permit is $100 per application, and a commercial structure has to schedule a fire safety meeting before approval. The county adopted the 2021 International Fire Code on October 27, 2025, with a Fire Marshal permit covering at least three site visits. No page checked names a county building permit as such, or a foundation permit. Permitting and Development, 830-393-8357.

• Medina County. The county's list of required permits has five items: 911 addressing, water well, floodplain, septic, and driveway and utility. No building permit, and no page checked names a building department or code edition. Medina County, 830-741-6000.

• Karnes County. The permitting page lists special projects and septic permits, and road and bridge permits. No page checked names a building permit, building official, building code or fire code permit. Special Projects and Permits, 830-780-3511.

• Frio County. Road and Bridge, under the County Engineer, handles septic, subdivision plats and right of way utility permits. No page checked names a building permit, building official, fire marshal or adopted code edition. Road and Bridge, 830-505-7402.

Checked at City of San Antonio Development Services, business and commercial projects, 2026-09-13.

Checked at City of San Antonio Development Services, FY 2027 development fee schedule, 2026-10-03.

Whole chapter checked; it gives counties no such power. Checked at Texas Legislature Online, Local Government Code Chapter 233, county regulation of housing and other structures, 2026-09-13.

On the Edwards Aquifer zones the plan gets approved before any concrete work starts. On the recharge, transition or contributing zone, construction cannot start until TCEQ approves a protection plan, and for the San Antonio region TCEQ lists Bexar, Medina, Comal, Uvalde and Kinney counties. On the recharge zone, nothing regulated happens without an approved water pollution abatement plan, and TCEQ's list covers putting up buildings, clearing, digging, and anything else that changes the lay of the ground, its geology or how it takes in recharge. Digging a footing is on that list. Zones and calendars: the Edwards Aquifer sheet.

The slab also counts as cover. TCEQ counts rooftops, driveways, concrete pads, sheds and sidewalks as impervious cover, which is the math behind the private-residence cases.

Stormwater goes by acreage, not zone. Work that disturbs an acre or more of soil, with stormwater running to surface water in the state, needs coverage under the TCEQ construction general permit, with a pollution prevention plan in place before construction starts. Five acres or more files a Notice of Intent through STEERS first; one acre to under five posts a signed small construction site notice instead; under one acre, off any wider common plan of development or sale, is outside the permit. Coverage does not free a lot over the aquifer: the permit bars construction there until TCEQ approves the protection plan.

Checked at Texas Commission on Environmental Quality, Edwards Aquifer Protection Program, 2026-09-13.

Checked at Texas Commission on Environmental Quality, Edwards Aquifer Protection Program, what plans you might need, 2026-09-13.

Checked at Texas Commission on Environmental Quality, Edwards Aquifer private residences, 2026-09-13.

Checked at Texas Commission on Environmental Quality, construction stormwater general permit TXR150000, 2026-09-13.

Checked at Texas Commission on Environmental Quality, general permit TXR150000, part II, 2026-09-13.

TDLR does not leave it out. Any building job with a total estimated construction cost of $50,000 or higher must be registered with TDLR, and the full construction set goes to a registered accessibility specialist for review under Administrative Rule 68.50. Below $50,000 the job need not be registered but is still held to the Texas Accessibility Standards, but the TDLR pages checked do not say whether a local jurisdiction or building official may require registration below $50,000, so ask the local office.

The figure that decides it is narrower than the budget. TDLR says to leave out the cost of buying the site, fees for architects, engineers or consultants, furnishings, and equipment that sits outside the building mechanical systems. TDLR lists what to take out, not what to put in, and concrete work is not on the take-out list, so settle the figure with the design professional filing the plans instead of assuming the slab is in or out. It is a sequencing point too, since registration and plan review come before construction. The walk-through: the TDLR sheet for jobs over $50,000.

Checked at Texas Department of Licensing and Regulation, Architectural Barriers frequently asked questions, 2026-09-13.

Checked at Texas Department of Licensing and Regulation, Architectural Barriers special project registration application, 2026-09-13.

One independent metal building contractor pours the slab or subs out the concrete, and a Texas professional engineer seals the foundation drawing.

Texas licenses no builder, so the credential on this drawing is the engineer's seal on the structural sheets.

Ask any contractor bidding the work to write six things into the estimate: which anchor bolt plan the slab is poured to, who seals the foundation drawing, whether a soil investigation is included, who pulls and pays for the permits above, who calls the inspections, and what concrete and reinforcing steel the drawing specifies. What moves the price: metal building cost in San Antonio. No metal building company serving the San Antonio area publishes a price for a finished slab.

Checked at Sunset Advisory Commission, Texas Residential Construction Commission; TDLR regulated industries list, 2026-09-13.

Checked at City of San Antonio Development Services, commercial project application guide, 2026-09-13.