Land Use · September 17, 2026 · Steven Owen

Five jurisdictions, five different answers: impervious cover on the US 290 corridor

The five buckets

Every tract on the corridor sits in exactly one of these, and the mailing address tells you nothing about which. A property with an “Austin, TX 78736” address can be in Austin’s ETJ, in Dripping Springs’ ETJ, or in neither.

Austin’s ETJ: the Save Our Springs ordinance reaches five miles out

Adopted by citizen initiative in 1992, the Save Our Springs ordinance lowered impervious cover to 15% of net site area in the Barton Springs recharge zone and 20% of net site area in the contributing zone, along with water quality standards requiring no degradation of runoff. What surprises buyers is its reach. Texas Local Government Code §42.021 gives a city of 100,000 or more an extraterritorial jurisdiction extending five miles beyond its limits, and Austin applies its environmental and water quality regulations throughout that ETJ even though it has no zoning authority there. So an unzoned, untaxed tract in unincorporated Hays County can still be carrying a 20% cap because it falls inside Austin’s five-mile ETJ and inside the Barton Springs contributing zone.

The measurement basis matters as much as the percentage. SOS limits are expressed against net site area, which backs out critical water quality zones and other constrained land before the percentage is applied. On a creek-crossed Hill Country tract, net site area can be dramatically smaller than the deed acreage — so a 20% cap on paper can behave like a 12% cap in practice.

The Dripping Springs ETJ: a different ordinance, a different math

Dripping Springs regulates water quality in its ETJ as well as inside its limits. Under the city’s Water Quality Protection Ordinance, codified at Code Article 22.05, impervious cover in the ETJ is capped at 35% in the Edwards contributing zone and 10% in the recharge zone. Inside the city limits the cap instead comes from the zoning district — general retail at 60%, commercial services at 70%, office and neighborhood services at 60%, limited retail and light industrial at 70% — with planned development districts available to go further.

Three details change the answer on a real site. First, the city measures against gross site area including buffers and critical environmental feature setbacks, which is more generous than Austin’s net-area approach. Second, existing impervious cover counts against the cap, so a tract with an old homestead, barns and caliche drives starts the clock partway used. Third, the ordinance has an anti-aggregation rule: a project is evaluated as a whole even if it is split into separate lots, so you cannot subdivide your way to more cover. Rainwater harvesting and porous pavement credits can buy back a limited amount of additional cover, and projects at or below 15% gross impervious cover skip the technical water-quality demonstration entirely — which is why some corridor projects deliberately design to that threshold.

Layered on top: water quality buffer zones set at platting and keyed to the stream’s drainage area, ranging from 50 feet per side on small drainages to 400 feet per side on the largest, plus a 150-foot setback from critical environmental features. Those are the lines that turn a rectangle into a much smaller buildable envelope.

Unincorporated county: fewer rules, different constraints

Where no city ETJ reaches, there is no municipal impervious cover cap at all. Hays County’s development regulations expressly incorporate the applicable city ordinances where they apply — the Dripping Springs ordinance in that ETJ, Austin’s in Austin’s, plus Buda, Kyle and San Marcos ordinances, the LCRA Highland Lakes ordinance and TCEQ Chapter 213 — but the county’s own 15% and 20% cover standards exist only inside its voluntary conservation development program, not as a general rule.

That does not mean unlimited. TCEQ’s Edwards Aquifer rules in 30 TAC Chapter 213, Subchapter B require an approved water pollution abatement or contributing zone plan for regulated activities disturbing five acres or more, or part of a common plan of development of five acres or more. There is no numeric cover cap in those rules, but permanent best management practices are required except for low-density residential at 20% or less impervious cover on lots of an acre or more. And where there is no sewer — which on this corridor is nearly everywhere — on-site sewage facility disposal area becomes the real density governor. We walk through that in water almost everywhere, wastewater almost nowhere.

Why the number moves the price

Development land is worth what a builder can put on it. Impervious cover is the direct translator between acreage and buildable product, and it compounds with everything else on the site.

Those are arithmetic illustrations, not entitlements — the usable figure on any specific tract depends on net versus gross measurement, existing cover, buffers, setbacks, floodplain and the disposal field. But the shape of the answer holds: the jurisdiction line is worth more per acre than almost anything else you can change about a piece of corridor land. It is also, uniquely, something that can sometimes be changed. Since September 1, 2023, Senate Bill 2038 has let eligible ETJ landowners petition out of a city’s extraterritorial jurisdiction, narrowed in 2025 by HB 2512. When the city being left is the one imposing the tighter cap, the effect on value can be substantial — we walk through a real example in how an ETJ release changed what a ±55-acre US 290 tract was worth.

How to find out which bucket you are in

Do not rely on the mailing address, the appraisal district’s taxing-unit list, or the listing broker’s summary. Pull the City of Austin Jurisdictions Web Map for the Austin answer, the City of Dripping Springs GIS or the official city limits and ETJ exhibit for theirs, the Edwards Aquifer zone boundary for recharge versus contributing, and the county’s development regulations for what applies where no city reaches. SCORE’s free Austin ETJ map checker answers the Austin half in one click. For the rest, send us the address.

How SCORE helps

Steven Owen is an Austin commercial real estate Agent who prices Hill Country land jurisdiction-first, because the jurisdiction sets the cover cap, the cover cap sets the buildable envelope, and the envelope sets the value. SCORE tracks jurisdiction, Edwards zone, CCN service area and floodplain for every parcel in its Central Texas database and prepares SB 2038 release petitions for eligible owners. See ETJ release and development land.

Sources and dates: City of Dripping Springs Water Quality Protection Ordinance, Code Article 22.05 (impervious cover by Edwards zone in the ETJ, gross-area measurement, anti-aggregation, credits, buffer zones and CEF setbacks) and Chapter 3 zoning district standards; Hays County Development Regulations (January 17, 2025), Chapter 4 and Chapter 765; City of Austin Save Our Springs ordinance (1992, 15% net site area in the Barton Springs recharge zone, 20% in the contributing zone); Texas Local Government Code §42.021; Texas Commission on Environmental Quality 30 TAC Chapter 213, Subchapter B. Ordinances are amended — confirm the current text and the zone determination for your specific tract with the applicable jurisdiction before relying on any figure here. This is general information, not legal, engineering or investment advice. Related: 290 corridor utilities · ETJ release case study · How to remove land from a city ETJ · Austin jurisdiction types explained.