Entitlement guide
Impervious cover.
Roofs, parking, drives and sidewalks all count. In many Central Texas watersheds, the impervious cover limit decides how big the project can be before anything else does.
The short answer
Impervious cover is any surface that keeps rain from soaking into the ground: buildings, pavement, and often compacted gravel. Cities and some counties limit it to protect creeks and the aquifer.
The limit is usually a percentage of the site, and the rules for what counts and how the site area is measured differ by jurisdiction and watershed. Some codes use gross site area. Others use a net site area that leaves out floodplain, steep slopes or buffers.
For an industrial or storage project, impervious cover can cap the building, the truck court and the parking together. It is often the single biggest number in early site planning.
- Watershed and aquifer zone for the parcel
- Impervious cover limits by watershed and zoning
- How the code measures site area and what it deducts
- Existing impervious cover on the site
- An impervious cover budget for the concept plan
Why it can stop a deal
Where projects get caught.
The limit is lower than the plan
A concept plan drawn without the watershed limit can show far more building and paving than the code allows.
Net site area shrinks the base
Where a code deducts floodplain, buffers or steep slopes, the percentage applies to a smaller area than the deed shows.
Rules are changing
Some Central Texas cities are revising water quality rules. A pending ordinance can change the limit before you file.
How it works
How it usually works in Central Texas.
Rules differ by city, county and utility, and they change. Treat this as orientation and confirm with the approving authority.
What counts
Buildings, paved parking and drives, sidewalks and patios usually count. Gravel, pervious pavers and pools are treated differently from code to code. We use the definition in the governing code, not a general rule.
How the limit is set
Cities often set impervious cover limits by watershed class and by zoning district. Watersheds that drain to the aquifer or to sensitive creeks usually have the tightest limits. The zoning district can add its own cap. The stricter limit governs.
Site area
Some codes apply the limit to the whole tract. Others first subtract floodplain, critical water quality zones, buffers or steep slopes to get a net site area. Where slopes count, a hilly site can lose more than a flat one.
County and state
Counties may limit impervious cover in some areas through their development rules. The state Edwards rules do not set a cap, but adding impervious cover over the aquifer generally triggers permanent water quality controls.
Options
Some codes allow transfers between tracts, credits for certain designs, or limited redevelopment exceptions. Each has conditions. We list the ones the code offers for your site and mark them as needing confirmation with staff.
Who decides
The people and offices involved.
| Who | What they decide |
|---|---|
| City planning and environmental review | Impervious cover limits and what counts |
| County development services | Limits on unincorporated land where they apply |
| Your civil engineer | The final impervious cover calculation on the plans |
| Your surveyor | Existing cover and slope data |
- Which watershed is the parcel in, and what is its limit?
- Does the code use gross or net site area?
- Does gravel count here?
- Is a new water quality ordinance pending?
- How much existing cover is already on the site?
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