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N.C. Department of Environment and Natural Resources

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Energy Mineral and Land Resources - Impervious Parking Legislation

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Impervious Parking Legislation

What parts of Senate Bill 845 (S.L. 2008-198) are related to impervious parking?

When will the requirements of the statute apply?

What areas of the state are affected by the requirements?

What size project must comply with the impervious surface area requirements?

What does the statute require?
Who will issue these permits?

What areas on a site will count toward the 20% permeable requirement?

Additional information about implementation of this statute


When will the requirements of the statute apply?

The bill was adopted into law on August 8, 2008. However, the provisions placing limitations on the percent impervious areas for vehicular parking lots will only apply to local permits issued on or after April 1, 2009.

What areas of the state are affected by the requirements? 

Basically, all areas of the state that are now under some state or federally-mandated stormwater program, such as Phase II, Water Supply, HQW or coastal counties stormwater are exempt from the requirements of this statute (see list below.)  In other words, if the area in question has no existing stormwater control requirements, the vehicular parking provisions of this statute do apply.

Areas of the state implementing any one of the following programs are not required to implement the impermeable parking limitations of Senate Bill 845:

(1) Water Supply Watershed I (WS-I) – 15A NCAC 2B.0212.
(2) Water Supply Watershed II (WS-II) – 15A NCAC 2B.0214.
(3) Water Supply Watershed III (WS-III) – 15A NCAC 2B.0215.
(4) Water Supply Watershed IV (WS-IV) – 15A NCAC 2B.0216.
(5) Freshwater High Quality Waters (HQW) – 15A NCAC 2H.1006.
(6) Freshwater Outstanding Resource Waters (ORW) – 15A NCAC 2H.1007.
(7) The Neuse River Basin Nutrient Sensitive Waters (NSW) Management Strategy – 15A NCAC  2B.0235.
(8) The Tar-Pamlico River Basin Nutrient Sensitive (NSW) Management Strategy – 15A NCAC 2B.0258.
(9) The Randleman Lake Water Supply Watershed Nutrient Management Strategy – 15A NCAC 2B.0251.
(10) Phase II Stormwater Management – S.L. 2006-246.
(11) Stormwater Requirements: Coastal Counties – 15A NCAC 02H .1005.

The Division of Water Quality has prepared a web-based Interactive Map for Stormwater Permitting to help development activities determine whether they are covered by a post-construction permitting program or other stormwater permitting requirements. By using the Interactive Map, it is relatively simple to determine whether an area, or an address, in question must comply with the provisions of the new parking surface statute. Basically, if the area in question is covered by any color other than gray, the area must meet other state or federal stormwater requirements and is exempt from the new statute provisions.

However, if the area is covered by a gray overlay, the requirements of this new statute apply. Please note that municipal boundaries are shown in red and those with gray underlayers must comply with the new statutes; those with other colors are exempt. Also, when the “Results” box appears to the left of the map, the “Category” results of “No Stormwater Program” identifies the areas where this new statute provision does apply.  Keep in mind that municipal boundaries and areas with stormwater controls do change without notice to the DWQ and it is possible that the maps contain errors.  Therefore, the DWQ maps should not be used as the final determinant for application of the impervious parking requirements.  Checking with the local governments and compliance with the wording of the statute will be the most accurate means of determining where the 80% pavement condition of this law applies.

For a statewide perspective, please see this map that identifies areas of the state where the various stormwater programs apply [NOTE - Please verify with the most current interactive map and with local governments]. The white areas indicate areas where no existing stormwater programs apply and would be subject to this new legislation. With the scale of this map, caution should be used in determining whether an individual site would be required to comply with the new parking area provisions.

What size project must comply with the impervious surface area requirements?

The development project must contain at least one acre of “vehicular surface area” which, by definition in the statute, includes: "means of ingress and egress to the area where passenger vehicles are parked” and “any median, traffic island, or other traffic control device or structure contained wholly within the vehicular parking area.” Therefore, the “vehicular surface area” will usually be much larger than just the area reserved for vehicle parking spaces. Covered parking areas or multilevel parking areas are not affected by the statute.  Buildings, patios, and walkways will not be included in the “one acre” determination. 

What does the statute require?

The statute requires that “No more than eighty percent (80%) of the surface area of the vehicular surface area may be impervious surface.” Impervious surface is defined as “any material that prevents the natural infiltration of water into the soil.” Therefore, vegetated areas within the “vehicular surface area” will count toward the 20% requirement for pervious surfaces. Also, permeable pavements such as permeable concrete, permeable asphalt, permeable interlocking concrete pavers, concrete grid pavers, and plastic reinforced grid systems can be used for credit toward the 20% requirement. Please see the “Permeable Pavement” section of the Division of Water Quality (DWQ) Stormwater BMP Manual for examples of permeable pavements. Generally, aggregate-covered parking areas are expected to result in compacted surface or subgrade layers and will be counted as impermeable area. However, systems designed with appropriate plastic or concrete grids that are expected to minimize compaction can be accepted as permeable for the purposes of meeting the 80% maximum specifications of this statute.

The DWQ Stormwater BMP manual does not recommend acceptance of permeable paving systems for stormwater credit in most areas of the central and western parts of the state. However, the DWQ has prepared Technical Requirements and Guidance for Permeable Pavement systems that all apply in all areas of the state covered by this statute.

The new statute also provides an alternative compliance method of treating the first two inches of runoff from “at least 20% of the vehicular service area” in an “appropriately sized bioretention area”. The statute specifies that the bioretention area must be designed “in accordance with standards established by the Department.” The Division of Water Quality has adopted guidance for bioretention areas where those are needed to comply with existing state and federal stormwater requirements across the state Those are provided in the “Bioretention” section of the state’s stormwater manual. However,  the technical specifications for using bioretention areas in areas of the state that must only comply with the provisions of Senate Bill 845 for Technical Requirements and Guidance for Bioretention.

Who will issue these permits?

The statutory changes that provide for implementation of this stormwater management condition do not specify the creation of any permit by Division of Water Quality but make it clear that it is to be a condition of issuance of the local government building permit approval.  Therefore, the implementation of the provisions of the statute will be the responsibility of the local government with the responsibility for issuing building permits. 

Some local governments have asked when local ordinances need to be developed.  After reviewing the statutes, the Division of Water Quality officials have concluded that additional local ordinance changes are not essential to require that these legislatively-mandated specifications be met prior to building permit issuance. Staff of the NC League of Municipalities has concurred with this conclusion.

What areas on a site will count toward the 20% permeable requirement?

The statue provides that if a “median, traffic island, or other traffic control device or structure” is contained “wholly within the vehicular parking area”, it can be considered as part of the “vehicular surface area.”  Therefore, any of those areas that are vegetated can be counted toward meeting the 20% pervious requirement.   If the “median, traffic island, or other traffic control device or structure”  is surrounded on all sides by parking spaces or pavement areas that are used as “means of ingress and egress” for private passenger vehicular traffic, then vegetated square footage in those areas can also be counted toward meeting the 20% pervious requirement.

If the surface is of an impermeable material, the square footage will be included in the determination of the “one acre or more” parking area calculation.  If the surface is vegetated, it will be included but can count toward the 20% impervious area required by the statute.

If a median or traffic island is not clearly surrounded by parking spaces, then the following criteria will be used: If the perimeter, or border, of the median or traffic control device is 75% surrounded by parking spaces or pavement used for "ingress” or “egress” to vehicular parking areas, then the area of the median or traffic control device is counted in the calculation of the “vehicular surface area.” However, if the median is bordered by a publicly-owned road, the adjacent vegetated area cannot be counted as part of the required 20% pervious area.  See these slides for examples.

Additional information about implementation of this statute

The Division of Water Quality will update this guidance when new information is obtained indicating changes are appropriate. Therefore, please reference this site periodically to learn of the changes. If you have questions, contact Mr. Boyd DeVane at boyd.devane@ncdenr.gov or at 919-807-6373.

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