Impervious cover limits are one of the most important — and least understood — factors affecting what Austin homeowners can build on their properties. Whether you’re planning an ADU, a room addition, a new driveway, or even a patio, impervious cover limits directly determine what’s possible on your lot.
What Is Impervious Cover?
Impervious cover includes any hard surface that prevents rainwater from naturally percolating into the ground. In Austin, impervious cover includes: building footprints (all structures on the lot), driveways and parking areas, concrete and paver patios, sidewalks and pathways, and pool decks.
Austin limits impervious cover to protect the Barton Springs watershed and reduce stormwater runoff that causes flooding. The limits apply across the city, though they’re most restrictive in the environmentally sensitive Barton Springs Zone.
Austin Impervious Cover Limits by Zone
Standard Urban Residential (Most of Austin)
Most SF-1 through SF-6 zoned properties in Austin are subject to 45% impervious cover limits. This means no more than 45% of your total lot area can be covered by impervious surfaces.
Barton Springs Zone (South and West Austin)
Properties in the Barton Springs Zone — generally south and west of downtown Austin — face more restrictive limits, often 25–40% depending on specific zoning and watershed location. These properties include much of the 78704 zip code, Barton Hills, Oak Hill, and areas along Barton Creek.
Impervious Cover Limitations and ADUs
The HOME Initiative expanded ADU rights significantly, but impervious cover limits remain a hard cap on what’s buildable. A homeowner who has already used 40% of their lot’s impervious cover capacity on their main house, driveway, and existing patio has limited remaining capacity for an ADU footprint.
How to Calculate Your Remaining Impervious Cover Capacity
TrueBuilt calculates impervious cover as part of every ADU and addition feasibility assessment. The calculation involves: total lot area (from Travis or Williamson County Appraisal District records), existing impervious cover (measured from site survey or aerial measurement), and remaining capacity calculation under your applicable zoning.
Strategies for Maximizing Buildable Area Within Impervious Cover Limits
When impervious cover limits are a constraint, TrueBuilt explores several strategies: pervious paver systems (which may receive partial impervious cover credit), green roof installations on ADU roofs, removal of existing impervious cover (old sheds, unused driveways), and optimizing the ADU footprint to maximize interior square footage within the available impervious cover budget.
Every Austin addition and ADU project TrueBuilt undertakes includes a complete impervious cover analysis to ensure your project is designed correctly from the start.