San Marcos is the Hays County seat, so the city permit office and the county permit office sit a few minutes apart — and the difference between them decides your whole build. The city carries a 3.5-mile extraterritorial jurisdiction, the largest in the county, and most barndominium-suitable acreage sits outside the city line.
Building around San Marcos
Start with the thing that surprises people: Texas counties cannot zone, and Hays County states it does not have or use zoning regulations for developing in the unincorporated areas. San Marcos, by contrast, zones under its Development Code and permits every square foot of new construction inside the city line.
The ETJ is the wrinkle. San Marcos counted roughly 67,500 residents in the 2020 Census, putting it in the 50,000–99,999 band of Local Government Code 42.021 — a 3.5-mile extraterritorial jurisdiction. Inside that ring the city controls subdivision and platting but has no zoning power and issues no building permits. Cross into unincorporated county and the county rules take over.
Senate Bill 2038 has reshaped that ring faster here than anywhere nearby. In the first six months after the law took effect in September 2023, 64 petitions removed roughly 3,715 acres from the San Marcos ETJ — more than Dripping Springs, Wimberley and Hays City combined. Released land loses the city’s impervious cover limits, water quality ordinances and aquifer recharge rules. Verify jurisdiction parcel by parcel; last year’s map may not hold.
What people build here
Two distinct patterns. West and north of town you see 2,000–3,000 square foot homes on 5 to 20 acres, view-oriented, with a detached shop. East and south toward Martindale and Staples, tracts are flatter and larger and builds skew toward working properties: bigger shops, equipment bays, sometimes a full shop-house with living quarters at one end.
Five acres is a meaningful number, not an aesthetic one. It is the threshold in TCEQ’s Edwards rules that exempts an individual landowner building one single-family residence from filing a protection plan — which matters more here than elsewhere in the county, because the Recharge Zone runs right through San Marcos.
Slab-on-grade is standard on the eastern tracts. West of the fault, expect pier drilling and a foundation engineer who wants a real soils report.
Permitting in and around San Marcos
| Item | Inside city limits | City ETJ (3.5 miles) | Unincorporated Hays County |
|---|---|---|---|
| Zoning | Yes — San Marcos Development Code | No zoning authority in the ETJ | None. Counties cannot zone in Texas |
| Building permit | Yes — Planning & Development Services, 630 East Hopkins | No city building permit. Subdivision and platting review only | No building permit. A Hays County Development Permit covers any development, including a house |
| Filing fee | $0.48 per square foot | Platting fees only | Development Permit fee varies by floodplain status |
| Plan review | 50% of the calculated permit fee, capped at $2,000 | Not applicable | None |
| Inspections | City inspections through construction | None by the city | None by the county. Builder hires a qualified third party for three inspections and files an attestation |
| Building code | City-adopted International Codes — confirm current editions | Not applicable | Builder attests the home meets the IRC as published May 1, 2008 |
| Septic (OSSF) | Hays County permits OSSF; city sewer available in most of the city | Hays County | Hays County. Permit required regardless of lot size |
| Aquifer | City Edwards Aquifer and watershed protection requirements apply | City water quality rules apply unless released under SB 2038 | TCEQ Edwards rules only |
Confirm current figures with Planning & Development Services before you budget against them.
What it costs around San Marcos
Published regional ranges, not quotes. West of I-35, rock is the budget killer. East of it, distance to power usually is.
| Line item | Typical range |
|---|---|
| Turnkey vertical build | $200–$350+ / sq ft |
| Shell only | $55–$85 / sq ft |
| Aerobic septic system, installed | $14,000–$25,000 |
| Water well, drilled and equipped | $20,000–$45,000 |
| Well water treatment | $2,000–$5,000 |
| Driveway | $15–$40 / linear foot |
| Culvert and road entry | $1,500–$5,000 |
| Electric service, overhead | $5–$15 / ft |
| Electric service, underground | $10–$25 / ft |
| Rock excavation | $30–$75 / cubic yard |
| Total site work, raw acreage | $52,000–$114,000 |
| City permit, 2,400 sq ft home | $1,152 filing fee, plus plan review |
Site notes for San Marcos land
San Marcos sits on the Balcones Fault Zone, which is why the springs are here at all. West of the fault: Edwards limestone, karst, voids, shallow soil. East of it: deeper soils and gentler grades. That single line moves your foundation cost more than any design decision you will make.
Aquifer review is usually not the obstacle people expect. Under TCEQ’s Edwards rules, an individual landowner building one single-family residence needs no protection plan when the lot exceeds five acres with one residence, when impervious cover stays at or below 20% of the property, or when the lot sits in a master community with an approved plan. Rainwater harvesting can bring adjusted cover under 20%. Where a plan does apply, budget 90 to 120 days for TCEQ review.
Groundwater districts split here. The Barton Springs/Edwards Aquifer Conservation District expanded south to San Marcos in 2015, but in that expanded territory it regulates only the Trinity; the Edwards Aquifer Authority oversees the Edwards. The Hays Trinity district covers western Hays County and does not reach San Marcos. Confirm which district your well falls under before contracting a driller.
Floodplain is not optional reading. The San Marcos River, the Blanco joining it just downstream, plus Purgatory, Sink and Willow Springs creeks all carry mapped floodplain through town. In the May 2015 flood the Blanco crested near 44.9 feet upstream at Wimberley after rising more than 30 feet in under three hours; 321 Hays County homes were destroyed. FEMA has revised maps here since. Pull the current panel, get an elevation certificate, build with freeboard.
County permitting
Hays County Development Services sits at 712 S. Stagecoach Trail in San Marcos. Outside city limits you need a Development Permit, an OSSF permit, and a builder attestation covering three third-party inspections. Full detail on our Hays County permitting guide.
Nearby towns
- Barndominium builders in Wimberley
- Barndominium builders in Dripping Springs
- Barndominium builders in New Braunfels
- Barndominium builders in Canyon Lake
San Marcos barndominium questions
Do I need a San Marcos building permit if my land is in the ETJ?
No. Inside the 3.5-mile ETJ the city reviews subdivision and platting but does not zone and issues no building permits. Your permits come from Hays County: a Development Permit and an OSSF permit for septic, plus a builder attestation covering three inspections. City water quality rules may still apply unless the tract was released under SB 2038.
What does a building permit cost inside San Marcos city limits?
The city charges a filing fee of $0.48 per square foot, and plan review at 50% of the calculated permit fee, capped at $2,000. A 2,400 square foot home starts near $1,152 in filing fee before plan review. Submittals include a digital site plan, four exterior elevations, energy calculations and a floodplain statement.
Does the Edwards Aquifer Recharge Zone block a barndominium in San Marcos?
Rarely for one home. TCEQ exempts an individual landowner building a single-family residence when the lot exceeds five acres with one residence, when impervious cover stays at or below 20% of the property, or when the lot sits in a master community with an approved plan. Inside city limits, the city’s own aquifer and watershed rules apply on top.
Which groundwater district regulates a well near San Marcos?
It depends on the aquifer and the parcel. The Barton Springs/Edwards Aquifer Conservation District expanded to San Marcos in 2015 but regulates only the Trinity there; the Edwards Aquifer Authority oversees the Edwards. The Hays Trinity district covers western Hays County and does not extend here. Confirm the district and its requirements before you sign with a driller.
Get matched with a builder near San Marcos
We are a referral site, not a builder. Tell us your acreage, target square footage, whether you are in city limits, the ETJ or fully unincorporated, and whether water and septic are sorted. We will match you with builders who work Hays County regularly and understand the attestation process, the Recharge Zone exemptions, and what the Balcones fault does to a foundation budget. Request your match here.
Cost ranges on this page are illustrative estimates compiled from Hill Country builders, licensed installers and public agency sources as of July 2026, not quotes — your site, finish level and rock conditions will move them. Government fees are as published by the issuing office on that date; confirm current amounts before you budget. This page is general information, not legal, engineering, or financial advice. This site is free to landowners and may be compensated by builders in its network.