Custom home construction in San Marcos
Iron C Construction is a custom home builder in San Marcos, TX, building new homes, additions, and remodels from our base up the road in Wimberley. Robert Castro founded the company in 2020, and the same small team that walks your lot also prices the home, runs the job, and hands you the keys. San Marcos is the Hays County seat, on I-35 between Austin and San Antonio, but it is not one kind of place to build. The city sits on the Balcones Fault, with Hill Country hills on the west side of town and blackland prairie on the east, two rivers running through it, and city limits that reach into three counties.
That mix is why two homes a few miles apart in San Marcos can have very different foundations, permits, and budgets. A good builder sorts out what your specific lot needs before anything is designed or signed, and that is where every new home we build starts.
Two kinds of ground in one city
West of the fault line, lots are rolling and rocky. Limestone close to the surface gives a home a strong base, but rock excavation costs more than digging soil, and a hillside lot changes the slab, the driveway, and the drainage. Getting the house, the drive, and the utilities to fit the slope starts with accurate layout, which is why we stake the site before the first form board goes in. Our guide to staking a new home on a sloped lot explains how that works.
East of the fault, the land flattens into blackland prairie. The dark clay soils there are known for swelling when wet and shrinking when dry, so the foundation is the part of the plan that matters most. On those lots we start with a soils report and build to an engineered foundation design sized for the movement the report shows, rather than assuming a standard slab will do.
Rivers, creeks, and the floodplain
The San Marcos River and the Blanco River both flow through the city, and the Blanco meets the San Marcos inside the city limits. Purgatory Creek, Sink Creek, Willow Springs Creek, and Cottonwood Creek drain through town as well. Plenty of good homesites sit near that water, and some of them sit in or beside a mapped floodplain.
The City of San Marcos takes this seriously. Under its floodplain ordinance, a building permit on a lot that is not already at least two feet above the city regulated floodplain also needs a floodplain permit, and a new building has to be built with its finished floor at least two feet above that floodplain. We check the flood maps before design starts, so the floor height, the foundation, and the site grading are planned for it from the first drawing.
Building over the Edwards Aquifer
San Marcos Springs, which feeds the San Marcos River, flows out of the Edwards Aquifer, and parts of the city lie over the aquifer’s recharge, contributing, and transition zones. Construction at a private residence on the recharge or contributing zone falls under the Texas Commission on Environmental Quality Edwards Aquifer rules. An individual plan is not required when the home is part of a master community with an approved plan, sits on a lot larger than five acres with only one home on it, or keeps impervious cover at or under 20 percent, including through rooftop rainwater harvesting. When none of those apply, the plan becomes part of the permitting schedule. We confirm which zone your lot is in early, because it can shape how much roof, drive, and slab the site plan can carry.
Permits depend on which side of the line you build
Inside the city limits, the City of San Marcos Permit Center reviews the building permit, and a single-family home on a legally platted lot has its site standards checked as part of that building permit. Outside the city, the county takes over. In unincorporated Hays County, every septic system and every development needs a county permit, including floodplain development permits, no matter how large the acreage is.
The county line matters here more than in most towns. San Marcos extends into Caldwell County to the east and Guadalupe County to the south, so a homesite on the edge of town can fall under a different county’s septic and floodplain review than a lot near the courthouse. We confirm the jurisdiction for your parcel at the start, then line up the permits, the survey, and the construction staking so the build moves from design to slab without long stalls.
What a custom home costs to build
The most common question is cost, and the honest answer starts with a benchmark. The median contractor-built custom home in the United States cost about $166 per square foot to build in 2024, not counting land, according to the National Association of Home Builders. Treat that as a starting point, not a quote, because the same dream home can price very differently on two San Marcos lots.
What moves the number in San Marcos is the lot. A hillside lot may add rock work and a longer driveway. A prairie lot may need a more substantial engineered foundation. A lot near a creek may need a raised floor and extra grading. A rural lot may need a well and a septic system, and where rock sits close to the surface Texas rules often call for an aerobic or other advanced system instead of a simple drainfield. We price from your land and your plan, with a line-by-line budget that shows those site costs up front, so you can compare building against buying with real numbers instead of a guess.
Homes and structures we build
Iron C Construction handles the full range of residential work with one local team:
- New custom homes, from the first design conversation through the final walkthrough.
- Build on your lot for owners who already have a homesite or acreage.
- Home additions that add space without losing the character of the house.
- Whole-home remodels and renovations for older homes that need more than a refresh.
- Custom barndominiums with a steel or post-frame shell and a fully finished interior.
- Garages, shops, and accessory structures for equipment, hobbies, and storage.
- Guest houses and casitas for family, a home office, or rental income.
How we run a custom build
Every home building project follows the same clear steps: site review and budget, design and selections, permitting, construction, and a final walkthrough. You know which stage you are in, what decisions are coming, and who to call. Robert Castro stays involved in the homes we take on, and Arthur Leyva, our Construction Coordinator, brings more than 20 years of field experience to keeping the daily work organized and on schedule.
When the site surprises us, like rock where the plans expected soil or clay that calls for a deeper foundation, we show you what we found, explain the options and the cost, and let you decide before work moves forward. That is what transparency from a builder looks like on a job site, and it is how we have built our name across the Texas Hill Country.
Start your San Marcos custom home
Whether your land is on a hillside on the west side of town, on open prairie to the east, or out past the city limits, Iron C Construction can help you plan a home that fits it. If your plans include a shop, office, or other commercial space, our construction services in San Marcos cover that side of our work too. Tell us about your lot, what you want to build, and any questions about building there, and we will help you find a clear path through budget, design, and timeline. Contact us to request a consultation, and read our reviews to see what homeowners say about working with our team.
