Johnston County, NC Building Setbacks & Zoning: Lot Coverage Limits (2026)

Johnston County Code § 14-105 creates the Water Supply Watershed Protection District (WSW), an overlay that layers additional standards onto the county's base zoning wherever a parcel drains toward a public water supply. Subsection (m), Built-upon area, is the district's lot-coverage limit and it splits the district into two zones. In the critical area, § 14-105(m)(1) caps built-upon area, meaning structures, driveways, parking, and any other impervious surface, at 24 percent for both residential development not covered by the district's separate minimum-lot-size rule in subsection (l) and for nonresidential development.

In the protected area, § 14-105(m)(2) allows 24 percent built-upon area where development includes a curb-and-gutter roadway system, rising to 36 percent without curb and gutter, or as much as 70 percent under the county's 10/70 option, which requires a county-approved stormwater best management practice to offset the added impervious surface. Where these limits conflict with the separate Johnston County Stormwater Ordinance, § 14-105(m)(3) directs that the more stringent of the two controls. The district also layers on a 50-foot vegetative buffer along perennial and intermittent streams under subsection (n), widened to 100 feet for development using the 10/70 option, and the Johnston County Board of Adjustment sits as the watershed review board for variance requests under subsections (o) and (p).

A property owner in the WSW district needs to know which sub-area, critical or protected, applies before estimating how much of a lot can be covered, since the swing between the tightest and loosest built-upon limits is 46 percentage points.