What Is the Buncombe County Steep Slope Ordinance?

The Buncombe County steep slope ordinance, codified at Section 70-68 of the county’s Land Development and Subdivision Ordinance, sets hillside development standards that apply when you subdivide land in unincorporated Buncombe County with an average natural slope of 25 percent or greater. It limits how much of the lot you can grade, how much you can cover with hard surfaces, how steep your cuts and fills can be, and when you need a geotechnical engineer. Several other rules stack on top: zoning overlays at high elevations, a separate retaining wall permit, lower erosion control thresholds for hillside lots, and North Carolina’s Mountain Ridge Protection Act. Each one can independently reshape or block a project.

When the Ordinance Applies to Your Property

Section 70-68 defines a “hillside area” as any lot, parcel, or tract that meets three conditions at once: it sits in unincorporated Buncombe County, it qualifies as a minor or major subdivision under Section 70-5, and its average natural slope is 25 percent or greater.¹

A tract with an average slope under 25 percent can still trigger the ordinance if 30 percent or more of it exceeds 35 percent slope on a submitted slope analysis. That second trigger catches a property that sits on a gentle ridgetop but drops sharply on the sides: the overall average comes out low, yet a third of the land is dangerously steep. Properties in this “drastic variation” category can be split into two development areas, one exempt area where at least 90 percent of the land is 25 percent slope or less, and one area that remains subject to the full hillside development standards.¹

One limitation matters for most individual homeowners. Section 70-68 applies specifically to subdivisions. If you already own a single recorded lot and plan to build one home without further subdividing, this ordinance does not govern your project directly. You will still face the zoning overlay, erosion control, stormwater, and retaining wall rules described below, but the hillside development application process itself is tied to the act of subdividing land.

How Slope Is Calculated

Buncombe County uses a specific formula to determine whether a tract qualifies. Every subdivision application in potentially steep terrain must include a contour map with intervals of five feet or less, and the applicant calculates the average natural slope using this equation:²

S% = 0.0023 × I × L ÷ A

S is the average natural slope of the parcel in percent
I is the contour interval of the map in feet
L is the total length of all contour lines within the parcel in feet
A is the area of the parcel in acres, including any land designated for future development
0.0023 is a constant that converts square feet into acres

Slope is measured in the land’s natural state before any grading begins. Previously approved development on part of the tract does not count toward the hillside area, as long as no further subdivision is proposed on that portion.¹

What You Can Actually Build

The core limits in Section 70-68 are caps on how much of a lot you can disturb and how much you can cover with impervious surfaces like roofs, driveways, and patios. These caps get stricter as slopes rise:

On slopes of 25 to 35 percent, no more than 30 percent of the gross lot area may be disturbed, and no more than 15 percent may be covered by impervious surfaces.
On slopes greater than 35 percent, maximum disturbance drops to 15 percent and impervious coverage is capped at 8 percent.
For communal infrastructure such as shared roads and utilities, maximum disturbance is 15 percent and maximum impervious coverage is 10 percent.²

An 8 percent impervious cap on a one-acre lot leaves you roughly 3,485 square feet for all combined hard surfaces. That has to cover the house footprint, driveway, walkways, and any outbuildings. Designs for the steepest tier need to be compact from the start.

Some areas of a parcel are off-limits to any development or disturbance at all: rock cliffs, wetlands, stream buffer areas, mapped floodways, and sites listed on the National Register of Historic Places.³ Those no-build zones come off the top of your usable area before the percentage caps even apply.

Engineering Requirements Above 30 Percent

Once natural slopes exceed 30 percent, you have to bring in a geotechnical engineer for any road construction on that portion of the tract. The engineer investigates for colluvial deposits, which are loose soil and rock that collect at the base of slopes and can fail under construction loads. The engineer’s recommendations become part of the application package.³

Fill slopes on land above 30 percent natural grade cannot be steeper than 2 horizontal to 1 vertical, and cut slopes cannot be steeper than 1.5 to 1, unless a geotechnical engineer specifically designs a steeper configuration. A global stability analysis is required for homesites on slopes of 35 percent or greater, or in areas the county’s Slope Stability Index Map designates as high or moderate hazard.²

These geotechnical studies typically cost between $1,500 and $5,000 for a straightforward residential lot, and complex sites with deep fills or suspected colluvial deposits run higher. The county will not process a hillside development application without the engineering work where it is required, so budget for it early.

Zoning Overlays at Higher Elevations

Beyond Section 70-68, Buncombe County’s zoning code adds two overlay districts that can apply even to single-lot construction. The Steep Slope/High Elevation Overlay District governs land above 2,500 feet in elevation where natural slopes reach 35 percent or greater. The Protected Ridge Overlay District applies to properties within a designated buffer on ridges above 3,000 feet in elevation that rise 500 or more feet above the adjacent valley floor.⁴ Both triggers in each pair must be met. A site at 2,500 feet with a 20 percent slope is not in the steep slope overlay.

North Carolina’s Mountain Ridge Protection Act

State law adds a hard building height limit on high ridgelines that overrides anything the county might otherwise allow. Under the Mountain Ridge Protection Act, no building on a protected mountain ridge may exceed 40 feet in vertical height measured from the top of the foundation. If the foundation sits more than three feet above the natural finished grade on the high side of the slope, that extra height counts against the 40-foot cap. No structure may protrude more than 35 feet above the crest of the ridge at its uppermost point.⁵

A “protected mountain ridge” under state law is one at or above 3,000 feet in elevation that rises 500 or more feet above the adjacent valley floor. The act applies in all counties that have not formally exempted themselves, and Buncombe County’s Protected Ridge Overlay mirrors these state thresholds.⁵

Retaining Walls Need Their Own Permit

Hillside construction frequently calls for retaining walls, and these have their own ordinance under Chapter 26, Article VIII. Retaining walls providing more than 10 feet of cumulative vertical relief require a certificate of compliance from the county before any building permit will issue.⁶ The rules scale with height:

Over 10 feet cumulative requires engineering certification that the foundation is adequate, materials meet code, soil conditions match design assumptions, and backfill and drainage systems comply with the plans.
Over 20 feet cumulative requires terracing. The lowest terrace can reach 20 feet, each successive level is capped at 15 feet, and at least 10 feet of horizontal terrace is required between levels.
Over 40 feet cumulative requires a licensed surveyor to document the wall’s location upon completion for long-term monitoring.⁶

If no substantial construction progress happens within one year of receiving the certificate of compliance, it expires and the owner must reapply.⁶

Erosion Control and Stormwater on Steep Lots

Buncombe County enforces its own erosion control rules, and the trigger is lower for hillside sites. Standard development requires an erosion control permit when disturbing one acre or more. Properties located in a hillside subdivision must obtain an erosion control permit for just a quarter acre of disturbance.⁷ That quarter-acre threshold catches even modest grading for one driveway or building pad on a steep lot.

North Carolina’s Sedimentation Pollution Control Act layers statewide rules on top. Any slopes left exposed during construction must be planted or otherwise stabilized within 21 calendar days of completing a grading phase. Any land-disturbing activity affecting more than one acre requires an approved erosion and sedimentation control plan filed at least 30 days before work begins.⁸

The county’s stormwater ordinance requires a separate stormwater permit for any residential development that disturbs one acre or more, or any commercial lot of one acre or more.⁹ On hillside lots where the impervious cap is 15 percent or 8 percent depending on slope, the hillside standard will usually be the binding constraint, but both reviews run in parallel and each can trigger plan revisions.

Application, Fees, and the Penalty for Starting Early

Hillside development applications go through the Buncombe County Planning and Development Department at 46 Valley Street in Asheville, or through the county’s online development portal.¹⁰ The technical submission must include a color-coded slope analysis map, the slope calculation for the tract and each proposed lot, hazard designations from the Slope Stability Index Map, overlay district boundaries, NRCS soils data, environmental features such as streams and floodplains, and a full site plan.² County erosion control staff note that the common reasons for disapproval are failing to clearly mark the limits of disturbed areas, not addressing streams or springs on the property, and slopes that exceed the allowable steepness limits.⁷

The county’s own fees are modest compared with the engineering costs. According to the fiscal year 2026 fee schedule:

Site plan review is a $25 flat fee for all new structures and site work projects.
Hillside development review for a minor subdivision of 4 to 10 lots adds $100 to standard subdivision fees.
Hillside development review for a major subdivision of 11 or more lots adds $100.
Hillside individual lot plan review is $50 per lot.
A variance application costs $350, plus $25 per additional lot.¹¹

If you start land-disturbing activities before obtaining a permit, all fees double.¹¹ Where a project cannot meet the standard hillside requirements, the developer may apply for a variance through the Board of Adjustment.

What the Rules Do Not Protect You From

Following the ordinance to the letter will not cover you financially if the slope fails years after construction. Standard homeowners insurance policies exclude landslides, classifying them as “earth movement” events. Standard earthquake policies do not cover landslides either. Property owners who want landslide protection typically need a Difference in Conditions policy sold through surplus lines insurers, which bundles coverage for landslides, earthquakes, floods, and mudflows.¹²

Mudflow is a distinct event and is covered under flood insurance available through the National Flood Insurance Program or private carriers. If your hillside lot sits in or near a mapped floodplain, a flood policy covers the mud and debris component but still excludes the ground-shifting damage from a landslide.¹² After Hurricane Helene’s impact on western North Carolina in 2024, those coverage gaps are not academic for Buncombe County property owners.

1
Buncombe County, NC. Buncombe County Code of Ordinances – Chapter 70 Subdivisions
2
Buncombe County Planning & Development. Hillside Development Application
3
Buncombe County. Buncombe County Zoning Ordinance
4
Buncombe County, NC. Zoning
5
North Carolina General Assembly. North Carolina General Statutes Chapter 113A – Article 14
6
Buncombe County, NC. Buncombe County Ordinance for the Permitting of Retaining Walls – Chapter 26 Article VIII
7
Buncombe County, NC. Erosion Control
8
North Carolina General Assembly. North Carolina General Statutes Chapter 113A – Article 4
9
Buncombe County. Buncombe County Stormwater Management Ordinance
10
Buncombe County. Customer Guide to Electronic Plan Review
11
Buncombe County. Buncombe County Fee Schedule FY2026
12
Insurance Information Institute. Insurance for Landslides and Mudflow