North Carolina Building Code and National Fire Protection Association (NFPA) standards require an 18-inch minimum clearance between the sprinkler head and the top of storage. The 18-inch requirement is not intended to limit the height of permanent shelving on a wall, if the shelving is incorporated into the building design and not directly below the sprinklers. Such shelving may extend above the 18-inch plane below the sprinkler. Shelving added to the building post-construction and any storage on the shelves may not extend above the plane 18 inches below the sprinkler head.