Impervious Cover

Any surface that prevents rainwater from percolating into the ground, such as rooftops, driveways, and paved areas; regulated by zoning and watershed rules.

Impervious cover refers to surfaces — rooftops, concrete driveways, asphalt parking lots, compacted gravel — that prevent stormwater from infiltrating the soil. Local governments, especially in water-sensitive areas of Texas such as the Edwards Aquifer recharge zone (Austin, San Antonio), set maximum impervious cover limits as a percentage of the total lot area. Exceeding the limit requires a variance or the use of engineered mitigation (permeable pavers, detention basins). Impervious cover calculations are reviewed during plan check for additions, new construction, and hardscape projects.

Why it matters for contractors

Projects that push against a parcel's impervious cover limit may require civil engineering, grading, or drainage work as a condition of permit approval — creating a secondary lead for those specialty contractors.