Building permits, zoning and septic rules in Hays County, Texas

Unincorporated Hays County requires a development permit for land modification inside or outside a floodplain, including houses, pools, sheds, slabs, fill and clearing¹. Interior renovation of a single-family house outside the floodplain is exempt⁶.

The Hays County Fire Marshal issues building construction permits for commercial buildings, public buildings, places of public assembly or access, and multifamily dwellings². Applicable projects follow the 2018 International Fire Code with local amendments and the 2018 International Building Code adopted by reference, effective January 2020². The county fire code excludes single-family homes, duplexes, triplexes and purely agricultural buildings where no workers are present and the public does not enter; other development requirements still apply².

New single-family homes or duplexes on vacant lots, and additions increasing an existing home’s square footage or value by more than 50%, need at least 3 third-party inspections: foundation before concrete, framing/mechanical before drywall, and completion³.

Austin, mainly in Travis County but extending into Hays County, issues its own building permits within its zoning jurisdiction; Austin Water handles septic systems within Austin’s full jurisdiction and designated annexed areas^8,9.

Reach Hays County Development Services at 2171 Yarrington Road in Kyle, Texas, by phone at 512-393-2150¹⁰. The office is open Monday through Thursday from 8 am to 5 pm and Friday from 8 am to noon¹⁰. Hays County Development Services handles development permits and septic (OSSF) permits for unincorporated land^1,5. For questions about the building code that applies to multi-family, public, or commercial buildings, the office directs you to the Hays County Fire Marshal's Office at 512-393-7300⁶.

Applications are submitted online through MyGovernmentOnline, and the county publishes a Development Services Fee Schedule effective January 2026^4,11. Some projects require public notice, including notice to contiguous property owners within 200 feet⁴.

Hays County states that, outside the San Marcos Regional Airport zoning regulations, it lacks zoning authority⁴. Because the county has no general zoning, no county ordinance sets minimum home size, lot size, setbacks, lot coverage or building height for unincorporated land outside the airport area, and no county zoning rule restricts RVs, tiny homes, manufactured homes or accessory dwellings there¹². Austin, which reaches into Hays County but lies mainly in Travis County, sets zoning inside its city limits; Austin Water regulates septic systems within Austin’s full jurisdiction and designated annexed areas^9,13. No zoning does not mean no regulation: the development permit still applies, and the county regulates land subdivision and platting through Development Services, with plat applications and subdivision construction plans⁴.

Hays County administers on-site sewage facility (OSSF) rules for unincorporated land under Texas Health and Safety Code Chapter 366, and the county requires a permit for every OSSF, whether new, replacement or altered, regardless of lot size or acreage⁵. The county will not issue an OSSF permit for land that violates the Hays County Development (Subdivision) Regulations⁵. Every residential structure must connect to a county-permitted OSSF or to a centralized sewage treatment facility permitted by TCEQ, and aerobic or advanced treatment systems need ongoing maintenance⁵. Only about 2.2% of Hays County soils are rated free of severe limits for a conventional drain field, so plan on a site evaluation and likely an engineered or aerobic system¹⁴. Texas lets an owner install an OSSF on his or her own single-family home only if the local permitting authority allows it, the owner also owns the land, no part is developed for sale or lease, and all local requirements are met; the owner needs the knowledge, skills and equipment, and installation helpers generally need the appropriate installer license, with exceptions for licensed electrical work and tank delivery/placement¹⁵.

Hays County has no zoning authority on unincorporated land outside the San Marcos Regional Airport zoning area; the absence of county zoning does not remove development or sanitation requirements^1,4,5. Land used for residential purposes must connect to a county-permitted OSSF or a TCEQ-permitted centralized sewage treatment facility, including off-grid residences⁵. A new single-family house on a vacant lot also needs at least 3 third-party inspections³. Ask Hays County Development Services about the development application and sewage arrangement for your proposed RV or tiny home before moving onto the land^5,10.

1. Confirm whether your parcel is unincorporated, inside a city's limits, or inside the San Marcos Regional Airport zoning area, since each has different rules⁴.
2. If you are dividing land, check the county's platting and subdivision process first; an OSSF permit will not issue on land that violates the subdivision regulations^4,5.
3. Line up your septic site evaluation early: only about 2.2% of Hays County's soils are free of severe limits for a conventional drain field, and Development Services permits OSSFs directly^10,14.
4. Apply online for your development permit before you build any new structure, addition or manufactured-home placement^1,4.
5. If your project needs access through county right-of-way, expect a driveway permit, submitted through the county portal¹⁶.
6. For a new single-family house or duplex, contract a third-party inspector before you start; the county requires at least 3 inspections and performs none itself³.
7. Start construction within 1 year of your permit's issuance, and finish within 2 years of issuance, or the permit expires⁶.
8. If your driveway will connect to a state highway, apply for a TxDOT permit (Form 1058) before you build it⁷.

Septic suitability deserves an early check on Hays County land: only about 2.2% of the county's soils are rated free of severe limits for a conventional drain field, so budget for an engineered or aerobic system and a site evaluation before you make an offer¹⁴. Land is in demand here: farmland has recently been valued around $11,177 an acre, and the typical home value is about $373,087¹⁴. Hays County is hilly and wooded, with 87% of land at 15% slope or less and about 50.9% forest cover, and gets a moderate 35.1 inches of rain a year with severe drought in about 29.4% of recent years¹⁴. Carrying costs run moderate to high: the effective property tax rate is about 1.7%, with a median bill around $6,420 a year, and a typical home insurance premium runs about $2,312 a year¹⁴.