What counts as impervious cover in Austin — the §25-8-63 list

Last verified August 13, 2026 against the Austin Land Development Code · Kimbrough Gray · KiliGray Homes

Roads, driveways, parking, buildings and concrete always count. The interesting cases are conditional: an uncovered wood deck with drainage gaps over pervious ground counts at half its area, gravel used only for landscaping or pedestrians counts as nothing, and the water surface of a ground level pool is excluded.

Applies to: Development subject to the impervious cover calculations in Section 25-8-63. Several exclusions in that section carry conditions on construction or location — gravel must sit over a pervious surface and without a compacted base, porous pavement is limited to pedestrian walkways and multi-use trails outside the Edwards Aquifer Recharge Zone — so the same feature can be excluded on one site and counted on another.

The part with no conditions

Six things count, full stop, with no test to apply and no way to design around them: roads, driveways, parking areas, buildings, concrete, and any other impermeable construction covering the natural land surface. That last phrase is the catch-all — if you have built something that stops water reaching the ground, it counts whether or not it appears by name in the list.

Scrap and metal salvage storage areas also count, which matters on industrial sites rather than houses.

What the code says

Impervious cover calculations include: (1) roads; (2) driveways; (3) parking areas; (4) buildings; (5) concrete; (6) impermeable construction covering the natural land surface; (7) for an uncovered wood deck that has drainage spaces between the deck boards and that is located over a pervious surface, 50 percent of the horizontal area of the deck; and (8) the portion of a site used for the storage of scrap and metal salvage, including auto salvage.

Austin Land Development Code · Read the full code

Feature	Counts?	The condition that decides it
Uncovered wood deck	Half	Only if it has drainage spaces between the boards AND sits over a pervious surface. A deck on concrete is concrete.
Gravel	No	Only where it is over a pervious surface, used only for landscaping or pedestrians, and has no compacted base. A gravel parking pad fails all three.
Pool	Water only	The water surface of a ground level pool, fountain or pond is excluded. Surrounding decking is not named in the exclusion list.
Porous pavement	Usually yes	Excluded only for pedestrian walkways and multi-use trails, designed to the ECM, and outside the Edwards Aquifer Recharge Zone. A porous driveway still counts.
Rainwater cistern	No	Ground level only — a subsurface cistern is not excluded.
Detention basin	No	Ground level only — subsurface detention is not excluded.
Public sidewalk	No	Only in a public right-of-way or public easement. A private walk on your lot counts.
Accessibility ramp	No	For an existing single-family or duplex unit, within the width limits, with no roof or walls, and subject to the building official.

Each exclusion in §25-8-63(C) carries a condition. The condition is usually where a plan fails.

The deck rule is the one people get wrong

An uncovered wood deck counts at 50 percent of its horizontal area — but only when both halves of the test are met: drainage spaces between the boards, and a pervious surface underneath. Miss either and you are back to the general rule, where the deck is impermeable construction covering the natural land surface and counts in full.

So a slatted deck over dirt is half. The same deck built over a concrete patio is entirely impervious — and so was the patio.

Gravel counts as nothing, until you compact it

Gravel over a pervious surface is excluded when it is used only for landscaping or by pedestrians and is not constructed with a compacted base. Those are the exact words, and each clause removes a common use.

A gravel path through a garden qualifies. A gravel parking area does not — it fails the pedestrian-only clause. And any gravel laid on a compacted base fails regardless of what you use it for, which is most gravel that is expected to carry weight.

Porous pavement is narrower than it sounds

The porous pavement exclusion is limited three ways at once: to pedestrian walkways and multi-use trails only, to designs meeting the Environmental Criteria Manual, and to locations outside the Edwards Aquifer Recharge Zone.

The practical effect is that porous paving does not solve a driveway problem. A porous driveway is a driveway, and driveways are named in the include list.

Subsurface versions are not excluded. Water quality controls, detention basins and rainwater cisterns are each excluded only in their above-ground form — the code says "excluding subsurface" in all three. Burying the tank does not buy the exclusion.

Common questions

Does a deck count as impervious cover in Austin?

Half of it, if it is an uncovered wood deck with drainage spaces between the boards and it sits over a pervious surface. If either condition fails — the boards are tight, or there is concrete underneath — it counts in full as impermeable construction.

Does gravel count toward impervious cover?

Not if it is over a pervious surface, used only for landscaping or by pedestrians, and laid without a compacted base. A gravel parking pad fails the pedestrian-only test, and anything on a compacted base fails regardless of use.

Does a pool count toward impervious cover?

The water surface of a ground level pool, fountain or pond is excluded by name. Surrounding decking, coping and equipment pads are not on the exclusion list, so they fall under the general rules for concrete and impermeable construction.

Does porous pavement reduce impervious cover?

Only for pedestrian walkways and multi-use trails, only if designed to the Environmental Criteria Manual, and only outside the Edwards Aquifer Recharge Zone. It does not help on a driveway, because driveways are on the include list by name.

Do sidewalks count toward impervious cover?

Sidewalks in a public right-of-way or public easement are excluded. A private walkway on your own lot is not covered by that exclusion.

Does a rainwater cistern count?

A ground level rainwater harvesting cistern is excluded. A subsurface cistern is not — the exclusion says "excluding subsurface cisterns" explicitly.

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We do this research ourselves on every project we take on — zoning, floodplain, watershed, trees, whether it is a legal lot. Send us an address and we will run it and tell you what we find. It works the same whether you own a vacant lot, a house you are thinking of adding a unit to, or a house you are thinking of replacing. No charge and no strings, and if it is a bad lot we will say so.

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We are homebuilders, not the City of Austin. This page explains how we read the code in practice — it is not legal advice and it is not an official determination. Always confirm with Austin Development Services before you rely on it for a project. The authoritative text is the Austin Land Development Code; permitting questions go to Austin Development Services Department.