Slope Construction, Considerations and Regulations, in Western NC

Western North Carolina (“WNC”) hosts the highest peak east of the Rockies in the United States in Mount Mitchell.  Due to the popularity and views of North Carolina’s Blue Ridge Mountains, people have always sought to move here and build in and on the mountains.  Many of these people desire to build houses with a view and, therefore, are looking to build on slopes, up mountainsides.  For a number of reasons, including, but not limited to, landslides, erosion, sedimentation, drainage, septic plans and needs, and other environmental, ecological, and safety issues, building on or at slopes, should be properly researched, planned, and implemented (if done at all in many locations).  It is important for contractors and landowners building or planning to build on slopes to be aware of the risks, social and environmental issues, and increased costs that come with such construction.

Over three quarters of the land in western North Carolina has a slope in excess of 30 percent.  Unfortunately North Carolina, as a state, has been unable to enact legislation to provide guidance and protection in slope construction.  Over the years there have been three state legislative efforts to establish a measure of control over steep slope building practices, but none have been successfully passed.  The primary state slope construction bill that has been percolating in the legislature all this time would require builders to consult an engineer when building on slopes that exceed a threshold of 40 percent.  Fortunately, in the State’s shadow of inactivity, local counties and communities have taken efforts to codify and provide ordinances for slope construction (discussed below).

Most engineers, and other people in the know, recommend that slope cuts and fills should not exceed a 30 percent grade.  For now, the situation is a buyer beware (“as is”) type of matter, wherein a prospective purchaser of land better commit him or herself to researching the property, including geology and soil makeup, prior to purchase to see if slope construction at site is at all possible and safe.  Even if someone “can” build on a slope, does not mean they should, and such construction will come with increased considerations, maintenance, costs, and responsibility to the fellow man and surrounding environment.

Why:

There are very serious reasons for slope construction legislation and planning in Western NC:

  • Landslides – Western North Carolina mountain home sites are susceptible to earth movement because of geologic features and water-reactive soils.  Landslides have also become more common in the last 20 years in the region partly because of the increase in slope construction, with improper planning and implementation, as well as construction in locations where homes should not be built.  Geologists and engineers urge professional assessment and expert planning when naturally unstable slopes are altered for residential development.   Landslides not only destroy homes and force sediment into local waterways, but endanger lives.
  • Erosion and Sedimentation – If the slope is too great, it is almost impossible to prevent/control erosion.  Erosion not only destroys the site and endangers a home to landslides and drainage problems, but it causes the sedimentation of our local waterways, which are one of primary natural advantages of the region.  As a source of life, our waterways provide opportunities for the local economy in the form of recreational activities, farming and wildlife, as well as the record diversity of flora and fauna that occur throughout WNC.  Sedimentation caused by erosion is one of the greatest dangers to our aquatic ecosystems, behind direct pollution and effluents.
  • Septic Systems – Approximately 75 percent of the homes in WNC depend on individual sewage treatment and disposal systems.  However, a large percentage of the land, 90 percent in some counties, has severe limitations for conventional septic systems.  Every prospective property owner should know that an adequate septic system has to be approved by the Environmental Health Section of the respective county health department before a new home is allowed to be occupied or connected to a source of electricity.  It is important to evaluate the site for septic suitability before purchasing the property.  Septic systems may not be located in cut and filled areas.
  • Flooding – Faster and increased runoff can cause increased flooding, which has become an all too real and present problem in the region.  Annual precipitation in portions of WNC is the highest in the eastern United States.  The steep, mountain slopes permit rapid storm-water runoff.  Decreasing natural use and absorption of rainfall by constructing developments and homes on slopes, especially improperly, can increase the rate and amount of runoff that then ends up in our valleys, creeks, and rivers, thereby endangering homes, businesses and lives at the lower levels.

How:

When construction occurs on slopes, some amount of leveling is necessary to prepare the house site and build an access road.  On steep slopes, leveling involves a process called cut and fill whereby rock and soil are cut from higher slopes and used to fill in the land below.  It is important to stabilize both the cut and the fill banks in order to control erosion/sedimentation and building site stability.  Slopes of cuts and fills should not exceed 30 percent grade, depending on the type of rock and soil that is present.  In other words, the cut bank and the fill bank should rise or fall no more than 30 vertical feet for every 100 feet of horizontal length.  The local Soil and Water Conservation District can assist you in evaluating your land for site stability and in developing plans to protect it.

Once cut and fill has occurred, vegetation should be established on exposed land as soon as possible.  It is important that native vegetation is used for this manner, as Western NC has a history of introduced invasive species that overrun the local flora and, potentially, the property as a whole.  Further, efforts should be made prior to the cut and fill work to preserve trees and vegetation on the building site, where possible, in order to assist with preventing erosion and protecting the site during excavation and grading.

Regulations and Ordinances:

Buncombe County is host to Asheville, the largest City in WNC and, because of that, hosts one of the largest populations of the region.  Buncombe County has attempted to enact ordinances to provide guidance for those interested in building on slopes through its Steep Slope/High Elevation Overlay District and Protected Ridge Overlay District tables.  These tables outline what kind of structures are allowed in what locations and on what sites.  They, however, do not necessarily provide guidance as to where it is not safe to build or what measures need to be taken during construction on certain slopes.  Other counties have either developed or are in the process of developing geological maps to highlight potential areas of instable soils and landslide concern.  Additionally, Haywood County has enacted slope construction ordinances, which can be found here: http://www.haywoodnc.net/downloads/engineering/SLOPE%20ORDINANCE(rev).pdf.  Finally, the North Carolina Building Code, Appendix J, on Grading, does provide rules and guidelines for grading, cut and fill, of slope construction sites (below).

Buncombe County’s Steep Slope/High Elevation Overlay District and the Protected Ridge Overlay District (Sec. 78-644 and 78-645, respectively, of the Buncombe County Building Code) were established in recognition that the development of land in steep, mountainous areas involves special considerations and requires unique development standards.  The Steep Slope/High Elevation Overlay District applies to property in Buncombe County at elevations of and above 2,500 feet above sea level and having a natural slope of 35 percent or greater, as specifically identified and delineated on the zoning map entitled “The Official Zoning Map of Buncombe County, North Carolina.”  Uses are permitted in the High Elevation/Steep Slope Overlay District pursuant to the Buncombe County table (located here, Pgs. 41-45: http://www.buncombecounty.org/common/planning/zoning/zoning_ordinance.pdf).

The Protected Ridge Overlay District applies to all Buncombe County mountain “ridges” whose elevations are at least 3,000 feet and whose elevations are 500 or more feet above the elevation of an adjacent valley floor and including 500 foot buffers measured horizontally from the center line of the ridge as specifically identified and delineated on the zoning map entitled “The Official Zoning Map of Buncombe County, North Carolina.”   Further, in accordance with North Carolina General Statutes §153A-342, the Protected Ridge Overlay District provides additional requirements on properties within one or more underlying general districts relating to the erection, construction, reconstruction, alteration, repair, or use of buildings, or structures including, but not limited to, height, number of stories and size of buildings and other structures.  Uses are permitted in the Protected Ridge Overlay District pursuant to the Buncombe County table (located here, Pgs. 48-51: http://www.buncombecounty.org/common/planning/zoning/zoning_ordinance.pdf).

Developers looking to design and install a hillside development (defined below) in Buncombe County, must fill out and submit a Hillside Development Application (http://www.buncombecounty.org/common/planning/HillsideDevelopmentAppChecklist.pdf).  Buncombe County defines a Hillside Development as a major or minor development, as defined by Sec. 70-5 of the Buncombe County Building Code, that has an average slope of 25% or greater, or has an average natural terrain slope of less than 25% but 30% of the tract has a slope greater than 35%.  Buncombe County’s Online Slope Calculator can be found here: http://www.buncombecounty.org/governing/depts/gis/News_Detail.aspx?newsID=7430.

Finally, regulations state that cut and fill slopes for both minor and major subdivisions shall be constructed to ensure adequate stability of the natural materials encountered. All storm drainage for both minor and major subdivisions shall be adequate to facilitate the road maintenance without excessive cost, and not cause flooding on private property from storm runoff of the design frequency. All pipe culverts, storm sewers and appurtenances shall be free of all debris and silt buildup and shall be structurally and hydraulically sound, and functioning in a normal manner. All drainage ditches shall be of such a width and depth and with such a slope as to carry the anticipated discharges. Paved ditches or riprap shall be required where necessary. Culvert sizing and materials shall meet or exceed the requirements approved by the NCDOT in “Subdivision Roads Minimum Construction Standards,” Utility Requirements, current edition.

According to NC Building Code on Grading (Appendix J), excavations of cut surfaces shall be no more than 50% slope, unless the owner or authorized agent furnishes a geotechnical report justifying a steeper slope (Sec. J106).  Similarly, the slope of fill surfaces shall also be no more than 50%, unless the owner or authorized agent furnishes a geotechnical report justifying a steeper slope (Sec. J107).

Finally, there is the North Carolina Erosion and Sedimentation Pollution Control Program, which affects most “land disturbing activities” and will be outlined and discussed in a subsequent blog article.  It is very much related to mountainside, ridge, and slope construction in addition to all kinds of general construction and development.

Both the landowner and contractor/developer can be liable for financial and legal penalties to the State, County, and adjacent landowners for not properly following rules and regulations pertaining to slope construction and related erosion and sedimentation.  The government could potentially stop or prevent construction and not allow individuals to move into and live in a violating home.

Mineral Rights in NC:

It is also important for prospective land purchasers and owners to know that under North Carolina law, ownership rights to the minerals on or under the ground can be severed from the surface rights to the land and transferred as a separate estate.  The owner of the mineral rights is legally entitled to use the surface of the property to reach and remove the minerals he or she owns.  Therefore, before one buys property, he or she should check the deed closely to determine whether the mineral rights have been severed and belong to someone other than the owner of the surface rights to the property.

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