Mountainsides & Steep Slopes

Loudoun County Mountains

The county's mountains were created by complex geologic processes. These areas contribute to Loudoun's beauty and quality of life, and are valued by residents and visitors alike. However, mountainsides are highly sensitive to land disturbance and development which can cause serious problems.

Steep Slopes

Steep slopes and moderately steep slopes occupy an area of approximately 50,000 acres in the county. Moderately steep slopes are areas with a 15% to 25% grade. Very steep slopes refer to more environmentally critical slopes of greater than 25%. If improper land use and disturbance occurs, these areas could experience erosion, building or road failure, and contribute to downstream flooding, as well as other health and safety hazards. Development on steep slopes often requires high volumes of clearing and "cut and fill." Such earth moving is subject to erosion and sedimentation that causes adverse effects on surface water quality and aquatic habitat. The Steep Slope Standards of the Loudoun County Zoning Ordinance apply to all very steep and moderately steep slopes in the county.


Mountains create an environment that contributes to the scenic character of rural Loudoun County. Mountainsides contain the headwaters to many of the county's streams and are important groundwater recharge areas. They have unique plant and animal communities and provide a variety of wildlife habitats.

Although the county's hills and mountains contribute to Loudoun's beauty and are valued by residents and visitors alike, they are highly sensitive to land disturbance and development. In addition to the destruction of prime viewsheds, uncontrolled land disturbance within these areas can cause major soil slippage, debris flows, or landslides. Disturbances that can initiate these land surface failures include removal of trees and vegetation; cutting, filling, or blasting of the soil and bedrock; and altering the soil moisture content by excessive groundwater withdrawal or changing surface water runoff.

Steep Slope

Loudoun County manages development on the mountainsides through a Mountainside Development Overlay District (MDOD) that contains land use restrictions and performance standards to minimize the destruction of individual resources and the disturbance of the ecological balance of these resources. Misuse of these critical areas may result in health and safety hazards. The boundaries of the MDOD are based on a range of both technical and aesthetic factors.


For questions or more information, please contact the Building and Development Department at 703-777-0220.