When planning a new pool, patio, or outdoor living space, there’s one term that can quickly shape what’s possible on your property: impervious surface area. While it might sound like zoning jargon, this measurement is one of the most important factors in pool design and permitting. It determines how much of your lot can be covered by hard surfaces such as concrete, pavers, or roofing, and it directly affects your layout, materials, and even the size of your pool deck.
What Is an Impervious Surface
An impervious surface is any material that prevents water from soaking into the ground. When rain hits these areas, runoff flows into storm drains, creeks, and retention ponds instead of being absorbed naturally. Because that runoff contributes to flooding and impacts local water quality, municipalities throughout North Carolina, including Raleigh, Cary, and Chapel Hill, regulate how much impervious surface a homeowner can add to a property. Many homeowners exploring custom concrete pools in Cary rely on these guidelines when planning new layouts.
Common Impervious and Pervious Materials
Understanding which materials count toward your limit is key to smart planning.
Typically considered impervious:
• Concrete driveways, patios, and pool decks
• Asphalt surfaces
• Pavers over compacted stone or concrete bases
• Roofs including home, garage, shed, or porch
• Pool coping
• Composite or wood decking installed over impermeable bases
Often considered pervious or partially credited:
• The pool shell itself, since water goes into water
• Mulch, grass, or planting beds
• Engineered pervious pavers designed for infiltration
• Composite decking over open soil or gravel
• Artificial turf with a permeable base
• Decorative gravel installed over sand or other porous material
Each municipality calculates these areas differently, so always confirm materials with your local planning office before finalizing your design.
How Are Impervious Limits Calculated
Each zoning district sets its own cap, often expressed as a percentage of your total lot size. For example, if your property is 20,000 square feet with a 15 percent impervious limit, that means you can have up to 3,000 square feet of hard surface including your home’s footprint, driveway, patios, walkways, and pool decking. If you live near a watershed area like Falls Lake or Jordan Lake, your limit may be even lower due to environmental protections.
What Happens If You Exceed Your Allowance
If a proposed design exceeds your impervious limit, your local jurisdiction may require one of the following.
Redesign: Adjusting the layout or materials to bring the total under the limit.
Mitigation: Installing an approved stormwater device to offset the additional runoff.
Common mitigation strategies include cisterns to capture and reuse rainwater, rain gardens that absorb runoff naturally, and dry sumps or infiltration pits that allow stormwater to slowly filter into the ground. Some municipalities even offer impervious credits for incorporating eco-friendly materials or disconnecting downspouts.
Making Smart Material Choices
If your design is close to the limit, material selection becomes crucial. Pervious pavers, elevated composite decking, and open-base designs can help maximize usable space while maintaining compliance. However, not every permeable material receives credit. The base installation and manufacturer specifications often determine how it’s classified. Before committing to any product, confirm with your local planning department or zoning office to ensure it qualifies.
Plan Ahead for a Seamless Design Process
Understanding impervious surface limits early helps ensure your pool is designed and built to meet every requirement. A detailed property survey gives your pool builder the clarity needed to plan efficiently, avoid costly revisions, and make the most of your space.
At Azalea Pools and Outdoor Living, we take the same thoughtful approach to every project. As a trusted Raleigh pool builder, we focus on creating spaces that fit naturally within their surroundings, meet every regulation, and reflect the way each family lives and relaxes.