According to ADA Accessibility Guidelines for Buildings and Facilities (ADAAG), the maximum slope ratio of a ramp should be 1:12, but the least possible slope should be used in ramp construction. The rise should not exceed 30 inches for any run in a ramp.
North Carolina requires access ramps to be between 44 and 48 inches in width. Federal standards state that ramps must be at least 36 inches wide; North Carolina, Washington and Wisconsin require the ramps to be wider to permit an ambulatory person to pass a wheelchair user.
The landing of the ramp must be as wide as the ramp itself (at least 44 inches in North Carolina) or as wide as the widest ramp run leading to the landing. If a ramp changes direction, a 60-inch by 60-inch landing is required.
Hand rails are required along both sides of the ramp segments and must be 30 to 34 inches high in North Carolina.
The cross slope (the slope measured perpendicular to the direction of travel, according to the Federal Highway Administration) can be at most ¼ inch in one foot (1:48) in North Carolina. The ramp should be constructed to exclude water puddling in the event of rain.