Residential Building Permits may be referred to stormwater management for review:
- Exceedance of allowable impervious limits
Each zoning district has a maximum impervious surface percentage that is allowed. The upper limit on residential lots is 30% impervious; however, subdivisions may range from 6% to 30% impervious depending on the level of stormwater treatment installed during development. During the subdivision approval process, the application and their design engineer determined what level of impervious the subdivision would have and whether stormwater devices would be installed for the entire subdivision.
Post-2006 subdivisions are recorded with a perpetuity statement, "Maximum Impervious Area Square Footage on each Individual Lot will be Stringently Enforced with no Exceptions into Perpetuity". Lots in these subdivisions are not permitted to deviate from the approved impervious on an individual lot basis. If there is no perpetuity statement, individual lot stormwater management may be permitted by application and installation of stormwater treatment. The application will be referred to stormwater staff for review.
Building permit applications are required to supply a plot plan which includes a scale drawing of the lot and the proposed impervious features (house footprint, driveway, sidewalks, porches, outbuildings, etc.).
Stormwater staff will contact the applicant to allow for revision of the plan or for potential deviation from the impervious requirement.
Note: In October 2012, the NC Division of Water Quality amended its Stormwater BMP Manual to allow more flexibility in the use of permeable pavement. Wake County will allow partial credit for permeable pavement in meeting impervious limits in some cases.
To receive pervious credits, a stormwater permit (see Deviation Process below) from Wake County is required. A stormwater plan must indicate that all State requirements are met including setbacks. An engineer's certification of the installation will be required.
Stormwater Deviation Process
For recently recorded lots, the recorded plats should list the maximum allowable impervious area per lot. For older subdivisions, you will have to determine your zoning district. When searching for your property's zoning district, iMaps can be a helpful tool to determine this criteria. Simply locate your property by searching by owner, an address, or PIN number. The first information shown is the attribute codes for the parcel data, which contains the zoning district. Once the zoning district is decided, you can check pages 3 & 4 of the stormwater deviation application form to determine the maximum impervious surface percentage allowed for that zoning district. You can refer to the Stormwater Rules letter, which explains how this rule came into effect.
Stormwater best management practices (BMPs) may be installed when a residential site plan is allowed to exceed the maximum allowable impervious surface coverage on that lot. Small deviations can be mitigated by the applicant or homeowner; however, large Stormwater Management devices should be designed by qualified professionals. A few solutions are listed below; however, keep in mind that there are many different possibilities for stormwater management.
Below are a few ideas for ways to mitigate the overage of impervious surface. Refer to the NC DWQ Stormwater BMP Manual
for detailed explanation.
Cistern (Irrigation Tank)
Dry detention basins
Deviation requirements include:
Please contact a Watershed Manager with any Stormwater Deviation questions at 919-856-7400.