How Impervious Surface Limits Can Affect Your In-ground Pool Installation

a swimming pool with a metal railing.

If you are in the planning stage of building an inground swimming pool on your property, you know there are a lot of details that are involved in getting the project off the ground. There are many rules and zoning ordinances that regulate outdoor projects in Raleigh, Clayton, Johnston County and surrounding areas. One critical factor in making the final plans for your pool, and one that should not be overlooked, involves impervious surface limits. Impervious surface limits are set to protect the environment by ensuring there isn’t water runoff that negatively impacts the soil surrounding your pool, including adjacent properties. At Prestige Pools, we deal with all the regulations and zoning ordinances that you encounter in your inground swimming pool project. In this article, we wanted to shed some light on impervious surface limits, specifically so you understand what they are and how these limits can affect your pool installation.

What Is An Impervious Surface?

An impervious surface is a manmade hard area that does not allow or significantly reduces water from precipitation to infiltrate the ground. Rain or melted snow runs off the impervious surface, picks up many types of pollution in the process,  and then flows into a storm drain or nearby body of water. The higher the volume of runoff, the more erosion occurs and results in larger amounts of unfiltered stormwater entering lakes and streams. Impervious surfaces are the most important factor that affects the amount of water flowing off a property, how quickly the water flows, and the amount of pollution that is picked up and carried with the water.

Here are some examples of impervious surfaces:

  • roofs
  • solid decks
  • patios
  • sidewalks
  • driveways
  • parking areas
  • roads
  • compacted gravel
  • concrete around an inground pool

How Does an Impervious Surface Impact the Environment?

The water cycle changes when there are large amounts of impervious surfaces. Places with little impervious surface areas. like a forest, allow rainwater to seep into the ground. The water is filtered by natural processes as it moves through the ground before it reaches streams and creeks. This process helps to keep the amount of water in streams and creeks from changing too much or too quickly. When an area has a lot of impervious surfaces, the water can’t seep into the ground. The polluted runoff increases, potentially causing more than 5 times as much water to quickly run off the land and into nearby bodies of water.

impervious limits for pool building

When more stormwater reaches streams and rivers, the risk of floods occurring increases. Streams flow faster, which causes the shape of the stream to change due to erosion. This causes a serious problem with more extreme flooding and damage to wildlife habitats. At the same time, because there is less moisture in the ground, plants and grass need extra water through irrigation in order to survive.

Studies have shown that local water bodies are less healthy when as little as 10% of an area is covered in impervious surfaces. When over 30% of an area is covered in impervious surfaces, nearby streams, rivers, ponds, and lakes can be severely damaged.

What Is My Impervious Surface Limit?

The impervious surface limit varies by county, town, and even neighborhood. It is different for individual zoning districts by each county. During the subdivision approval process for a residential area, the design engineer determined what level of impervious the subdivision would have and whether stormwater devices would be installed for the entire subdivision. Each zoning district has a maximum impervious surface percentage that is allowed.

A typical calculation for impervious surface for a property can look like this:

“The percentage of impervious surface is calculated by dividing the surface area of existing and proposed impervious surfaces on the portion of a lot or parcel that is with 300 feet of the ordinary high-water mark by the total surface area of that portion of the lot or parcel that is within 300 feet of the ordinary high-water mark and multiplied by 100.”

Understanding Impervious Surface Limits for Your Home

Wake County

For single residential lots in Wake County, the upper limit is 30% impervious. However, subdivisions can range from 6% to 30% impervious depending on the level of stormwater treatment that was installed during development. For more information about Wake County Stormwater Review and Permitting, click here.

Johnston County

Johnston County provides information on residential impervious surfaces, also called built upon areas (BUA), restrictions. Click here for information on when approval from Johnston County is required.

Town of Cary

The Town of Cary has specific requirements for swimming pool locations, pool decking, and pool barriers. Click here for information on the limitations on impervious surface area and density in Cary.

Town of Apex

The Town of Apex regulates the measurements for setbacks, lot sizes, and other specifications for buildings. Pools, both above-ground and in-ground, can be located no closer than 5′ from the side or rear property line. For information about impervious limits in Apex, click here.

Harnett County

For information about Harnett County construction permits and inspections, see the Harnett County website.

Town of Holly Springs

Contact either the town planning department for Holly Springs or Wake County to find out what the impervious surface limits are for your subdivision.

Obtain a Current Survey of Your Property

You’ll need a current survey of your property that includes all of the existing structures, concrete surfaces, sheds, distances to property lines, etc. Typically, your builder will provide you with a final survey with your home’s closing documents. Otherwise, you’ll need to obtain a survey from a licensed survey company.

Contact Prestige Pools of NC for In-Ground, Vinyl Liner Pool Installation

At Prestige Pools, it is our business to know the aspects of building an in-ground pool. We can help you navigate the intricacies of determining your impervious surface limits during the pool-building process. if you are ready to start the process of an in-ground pool addition to your home, please contact us at 919-586-8556 or fill out our online contact form.