Circle C Patios & Hardscape: Impervious Cover Limits

In much of Austin, a new patio is a simple design question. In Circle C, the first question is a number: how much impervious cover does your lot have left? The neighborhood sits in the Barton Springs Zone, where water quality protections are stricter than almost anywhere else in the city, and many lots were built close to their limits.

Where your limit comes from

Circle C was planned under approvals that predate or run parallel to the 1992 Save Our Springs (SOS) ordinance. The SOS percentages (15%, 20% and 25% of net site area, depending on the zone) are what most people hear about, but your lot's actual limit may come from:

• the subdivision plat and its notes;
• development or settlement agreements that governed the subdivision;
• deed restrictions and HOA rules;
• the zoning and watershed rules applied when the lot was approved.

Pull your plat and deed restrictions, and if anything is unclear, ask the city during residential review or a pre-submittal consultation. A licensed surveyor can measure existing impervious cover (roof, driveway, walks, patios) so you know your remaining allowance.

Exempt from a permit doesn't mean exempt from the limit

Austin exempts flatwork (sidewalks and driveways not more than 30 inches above grade, not over a basement, not in a flood hazard area) from building permits. A ground-level patio may need no building permit at all, but impervious cover limits still apply, and exceeding them can cause trouble when you sell or apply for a future permit.

Designing within a tight allowance

• Swap, don't add. Remove an unused walkway or part of a wide driveway and put the area into the patio you'll actually use.
• Consider surfaces that may be counted differently. Ask how the city will treat permeable pavers, gravel or decomposed granite before assuming they don't count.
• Use elevated wood decks with spaced boards where a slab won't fit the allowance. Confirm how they're counted.
• Size to use. A 12×16 seating area may serve better than a sprawling patio that uses your entire remaining allowance.
• Pools combine water surface, coping and deck. Map the whole footprint before you sign with a pool builder.

Limestone and slopes

Southwest Austin soils are shallow over limestone, so:

• excavation for patios, walls and footings often hits rock. Ask for a rock clause or unit price;
• natural limestone and flagstone are local, durable choices that fit the setting;
• retaining walls over 4 feet, or supporting a slope or driveway, need permits and usually engineering.

Water management, the reason for the rules

Hardscape here should slow and spread runoff, not concentrate it:

• slope surfaces toward planted areas rather than straight to the street;
• use dry creek beds or rain gardens to soak up runoff;
• don't direct downspouts onto patios that drain to the curb.

Cost context

HomeGuide's December 2025 patio guide puts installed patios at $5 to $35 per square foot nationally, depending on material. In Circle C, rock excavation, drainage and survey costs can add to that.