It is hereby made the duty of every property owner whose vacant or non-developed property abuts upon any street that has been improved with a hard-surface pavement to construct a concrete sidewalk conforming to city ordinances. This construction shall be required when 50 percent of the lineal distance of the sidewalk of said block has already been installed. Said construction shall be completed within one year after notice by the city engineer. (Ord. 4413 §4, 1987).