Concrete slab and foundation for a metal building in the Austin area

Every column in a pre-engineered package bolts to something already in the ground, so the erector's first day depends on a cured slab or pier footings with anchor bolts set in the pattern the building's own drawings call for: the right diameter and projection at each column, level across the footprint, in concrete cured to the strength the foundation sheet names. One Texas manufacturer's product pages spell out the split: the kit price covers the kit only, and the company does not provide the foundation or offer installation or erection. The column reactions come with the drawings; the foundation designer sizes the footings and the slab from them and from the soil, which is why the foundation is designed from the building's own drawings and not a generic detail.

The foundation contractor who reads the frame reactions prices the slab, and an independent local metal building contractor who works your county can carry the slab and the erection on one contract, or an owner who bought the package can bring the slab and the erector to it. The whole sequence is on the Austin area metal building guide.

SourceMueller, Inc., Standard Series Big Workshop 30 x 40 x 12 and Big Barn XL 40 x 60 x 16 product pages, and its Texas branch location pages, read 2026-09-20.

A Texas professional engineer seals the foundation whenever the permitting office asks for sealed sheets, and the statute's exemption is narrow. Occupations Code 1001.056 exempts the plans for a building of no more than one story and 5,000 square feet with no clear span over 24 feet on the narrow side, provided no engineering services are offered to the public; under that size an unsupported span over 24 feet still needs its roof supporting members engineered or pre-engineered. A private dwelling and its garage and a private farm, ranch or agricultural building are exempt too, and section 1001.056(c) withdraws the exemption for a residential slab on expansive soil unless the work meets the International Residential Code as applied in the jurisdiction. The architecture chapter reads the same way about who prepares the sheets: Occupations Code 1051.606 exempts a person who does not hold out as an architect and who prepares plans for a privately owned commercial building of no more than two stories or 20,000 square feet.

The offices set their own bar. Inside Austin, the commercial checklist says plans for a building over 5,000 square feet are sealed by a professional engineer, and structural plans for new construction list a site-specific geotechnical report. In unincorporated Travis County the non-residential development permit carries a site plan sealed by a Texas-licensed engineer, the Fire Marshal's plans go in stamped by a Texas licensed engineer, and the county pages read describe no structural plan review by the development office. Bastrop County's non-single-family development permit takes a civil plan set stamped by a Texas-licensed professional engineer; Caldwell County's commercial site construction permit needs engineer-certified drawings. Unincorporated Williamson County lists no building permit, building code or plan review for a commercial or accessory structure, so no county office reads the foundation sheet; the Fire Marshal's review there is a non-structural architectural plan review.

SourcesTexas Legislature Online, Occupations Code Chapter 1001, engineers, read 2026-09-20; Texas Legislature Online, Occupations Code Chapter 1051, architects, read 2026-09-20; City of Austin Development Services, commercial building plan review and inspection permit fees (FY 2025-26) and the commercial building application checklist, read 2026-09-20; Travis County TNR Development Services, Commercial Site Plan, read 2026-09-20; Travis County Fire Marshal, permits and plan reviews, and Travis County Code Chapter 201, read 2026-09-20; Bastrop County Development Services, and the Development Services application fees, read 2026-09-20; Caldwell County Development Ordinance, revised February 14, 2023, and the subdivision and development fee schedule, read 2026-09-20; The source was read and does not list this.Williamson County, frequently asked questions, infrastructure and developers, read 2026-09-20; Williamson County Fire Marshal, construction permits, and the Williamson County Fire Code, second edition, read 2026-09-20.

It tells the engineer what the dirt will do, so the slab is designed for the ground rather than a textbook average. Austin's commercial checklist is the record read for this site that lists a site-specific geotechnical report with the structural plans, and no other city or county record read here names one. The surveys explain why an engineer wants one anyway: the 1978 Caldwell County survey says the Crockett-Heiden soils, about 41 percent of that county, have high shrink-swell potential and high corrosivity to uncoated steel, so construction sites need extensive study, and the 1979 Blanco and Burnet survey says soils may be shallow to bedrock or too unstable to serve as a foundation. The surveys give the county-scale answer; a boring on the lot gives the parcel-scale one.

SourceCity of Austin Development Services, commercial building plan review and inspection permit fees (FY 2025-26) and the commercial building application checklist, read 2026-09-20.

It moves the slab, and the surveys say so in plain words. East of the escarpment the 1974 Travis County survey groups the Blackland Prairie soils as mainly clays with high shrink-swell potential and says shrinking and swelling causes much damage to building foundations; Houston Black soils, about 21 percent of the county with Heiden, are deep clays that crack when dry and are very slowly permeable when wet. The 1983 Williamson County survey puts the Branyon-Houston Black-Burleson soils at about 27 percent of that county, with dry-season cracks up to four inches wide and 20 inches deep, and says buildings and streets buckle and crack if not properly constructed.

So the design starts from the movement, not the load: the engineer stiffens the slab, deepens the beams or bears below the active zone so the building does not ride the wet-and-dry cycle. The statute follows the same logic, pulling the small-building exemption for a residential slab on expansive soil unless the work meets the residential code. A commercial metal shop on the same clay gets to an engineer through the offices above.

SourcesTexas Legislature Online, Occupations Code Chapter 1001, engineers, read 2026-09-20; USDA Soil Conservation Service, Soil Survey of Travis County, Texas (1974), climate and parent material sections, read 2026-09-20; USDA Soil Conservation Service, Soil Survey of Williamson County, Texas (1983), natural resources and parent material, read 2026-09-20.

It gives the footing something solid to sit on and makes every trench and beam an excavation in rock. The 1983 Williamson County survey says the limestone under the Eckrant-Georgetown unit at about 19 percent of the county and the Denton-Eckrant-Doss unit at about 21 percent, gives a good base for foundations and streets but is hard to excavate, with the typical Eckrant profile reaching fractured rock at 11 inches. West of the escarpment in Travis County the 1974 survey puts the Brackett association at about 38 percent of the county, describes Tarrant soils as about eight inches of stony clay over limestone, and names breaking and moving massive limestone for site leveling as the main urban limitation there. The Bureau of Economic Geology puts the escarpment in Austin roughly along MoPac, deep soils east of it and thin, rocky soils west.

Burnet County runs the same ground into the Llano Uplift: the 1979 Blanco and Burnet survey says shallow limestone soils make up about 74 percent of the survey area, and on the granite side Keese soils are 11 to 20 inches over indurated granite. A foundation on any of it is easy to bear on and slow to cut; the pad grading guide covers the site work.

SourcesUSDA Soil Conservation Service, Soil Survey of Travis County, Texas (1974), general soil map and engineering uses of the soils, read 2026-09-20; Bureau of Economic Geology, University of Texas at Austin, Geologic Wonders of Texas: Central Texas, read 2026-09-20; USDA Soil Conservation Service, Soil Survey of Williamson County, Texas (1983), general soil map unit 1 and the Houston Black series, read 2026-09-20.

One row per county from its USDA soil survey, read 2026-09-20; the last column is the survey's own sentence, shortened.

Two counties carry sand. Bastrop's Patilo soils are about 52 inches of loose fine sand with a perched water table at 48 to 72 inches after heavy rain, and Lee's Padina-Robco-Silstid unit is very deep sand with seepage as its limitation, so on sand the engineer's question is water under the slab more than movement.

SourcesUSDA Soil Conservation Service, Soil Survey of Travis County, Texas (1974), climate and parent material sections, read 2026-09-20; USDA Soil Conservation Service, Soil Survey of Williamson County, Texas (1983), natural resources and parent material, read 2026-09-20; USDA Soil Conservation Service, Soil Survey of Bastrop County, Texas (1979), woodland, general soil map and the Patilo series, read 2026-09-20; USDA Soil Conservation Service, Soil Survey of Caldwell County, Texas (1978), introduction, general soil map and how the survey was made, read 2026-09-20; USDA Natural Resources Conservation Service, Soil Survey of Lee County, Texas (2007), introduction and general soil map units, read 2026-09-20; USDA Soil Conservation Service, Soil Survey of Blanco and Burnet Counties, Texas (1979), introduction and general soil map, read 2026-09-20.

It raises the finished floor and puts an elevation certificate into the permit file, and each county sets its own line. In unincorporated Williamson County a new non-residential structure in the special flood hazard area has its lowest floor at least one foot above base flood level or is floodproofed with an engineer's or architect's certification, and the $75 Floodplain Development Permit requires a sealed FEMA elevation certificate after the slab and again at completion; outside the floodplain the county's $25 Certificate of Compliance verifies that no 100-year floodplain exists at the proposed development. Caldwell County's development ordinance puts a finished floor within 300 feet of a floodplain two feet above base flood elevation.

In an identified flood hazard area in Lee County a non-residential structure has its lowest floor at or above base flood elevation or is flood-proofed, certified by a licensed engineer or land surveyor, with an elevation certificate, where required, due within 10 business days of foundation completion. Burnet County's $400 Class B building permit, inside a designated flood hazard boundary, adds a site plan showing the flood zone and either a surveyor's elevation certificate or an engineer's letter; on the $25 Class A permit outside it the county page describes no structural inspection. The engineer sets the top of slab from the base flood elevation the county names, and the certificate after the pour proves it landed there.

SourcesWilliamson County, floodplain management, and the Flood Damage Prevention Order, read 2026-09-20; Caldwell County Development Ordinance, revised February 14, 2023, and the subdivision and development fee schedule, read 2026-09-20; Lee County Development Services Department, read 2026-09-20; Lee County, floodplain development provisions and the Flood Damage Prevention Ordinance, read 2026-09-20; Burnet County, on-site sewage facilities and development permits, read 2026-09-20.