Hays County

Hays County regulates construction in unincorporated areas through the Hays County Development Services Department. Because the county has no zoning authority, the department does not restrict whether an ADU may be built — it regulates only subdivision/plat compliance, on-site sewage (OSSF) compliance, floodplain compliance, 911 addressing, and county road access. A detached secondary dwelling on an unincorporated parcel is permitted as an ordinary residential structure; there is no separate 'ADU permit' because there is no county use category for accessory dwellings. Significant ADU activity in Hays County occurs in incorporated cities (notably the City of Austin partial overlap, San Marcos, Kyle, and Buda), each governed by city-level permitting.

Process overview: Typical workflow for a new accessory residential structure on an unincorporated Hays County parcel: (1) confirm parcel is in unincorporated Hays County (not inside any city or city ETJ with extra-territorial platting authority); (2) submit development application; (3) OSSF (septic) review by Hays County Environmental Health if not on public sewer (a new dwelling on a septic lot requires a separate OSSF permit under TCEQ rules); (4) floodplain review if within a mapped Special Flood Hazard Area; (5) 911 address assignment; (6) driveway/road permit if county road access. Hays County does NOT operate a residential building inspection program in unincorporated areas — Texas counties may not adopt building codes outside specific authorities.

Impact fees: Hays County does not levy municipal-style impact fees on residential construction in unincorporated areas; there is no county school, park, or traffic impact fee schedule. Fees are permit-processing fees only.

Hays County itself does not appraise real property. Under Texas Tax Code Chapter 6, property-tax appraisal is performed by a single countywide central appraisal district. For Hays County, that body is the Hays Central Appraisal District (Hays CAD), a political subdivision of the State of Texas. The Hays County Tax Office handles collection but not appraisal. An ADU is assessed as an improvement to the host parcel: Hays CAD adds the ADU's appraised value to the parcel's total improvement value on the next revaluation cycle and the homestead cap under Texas Tax Code Sec. 23.23 (10% annual cap on homestead appraisal increases) applies to the parcel as a whole if the parcel carries a residence homestead exemption.

Assessment policy: Texas property appraisal runs on an annual cycle (Tax Code Ch. 25). Hays CAD values all real property at market value as of January 1 each year. An ADU completed between January 2 and January 1 of the following year is captured on the next appraisal cycle. The homestead-cap under Tax Code Sec. 23.23 limits the annual increase in appraised value of a residence homestead to 10% (excluding new improvements). Owners who disagree with the appraisal file a Notice of Protest with the Appraisal Review Board by May 15 (or within 30 days of the Notice of Appraised Value, whichever is later).

Hays County's county-level overlays apply only inside its unincorporated footprint. The principal overlays are FEMA-mapped Special Flood Hazard Areas administered by Hays County Development Services under the county's floodplain ordinance, and on-site sewage facility (OSSF) jurisdiction under TCEQ delegation. Hays County sits over the Edwards Aquifer recharge zone in its western portion, which adds Edwards Aquifer Protection Plan requirements for any development including ADUs over the recharge zone — administered jointly with the Texas Commission on Environmental Quality. Inside incorporated cities, overlay administration is a city function. There is no countywide WUI / wildland-fire hazard overlay with binding building-code effect at the Hays County level.

• Hays County Floodplain Management (FEMA NFIP participation) — A new ADU in a Zone AE parcel must be elevated to or above the Base Flood Elevation per the county ordinance.
• Edwards Aquifer Recharge Zone protections — An ADU adding more than minimal impervious cover may trigger TCEQ submittal regardless of whether the underlying parcel is in city or county jurisdiction.
• On-Site Sewage Facility (OSSF) jurisdiction — An ADU counts as an additional dwelling for OSSF sizing purposes, which can trigger system expansion on undersized lots.