Any building requiring yard space shall be located at such an elevation that a sloping grade shall be maintained to cause the flow of surface water to run away from the walls of the building. A sloping grade, beginning at the sidewalk level, shall be maintained and established from the center of the front lot line to the finished grade line at the front of the building, and from the rear wall of the building to the rear lot line; however, this shall not prevent the grading of a yard space to provide sunken or terraced areas, provided proper means are constructed and maintained to prevent the unreasonable runoff of surface water to flow onto the adjoining properties. When a new building is constructed on a vacant lot between the existing buildings or adjacent to an existing building, the existing established grade shall be considered in determining the grade around the new building, and the yard around the new building shall be graded in such a manner as to meet existing grades and not to permit unreasonable runoff of surface water to flow onto the adjacent properties. Grades shall be approved by the Administrative Official.