Side yard: on each side, not less than 7 1/2 feet in width, free from all encroachments such as overhanging eaves and cornices, porches, steps, cellar doors, etc., on each side of a one-family dwelling, unless, prior to the effective date of this chapter, lots have been accepted by the Westmont Borough Council with less than 75 feet of frontage on any Borough street, and in that event, the side yard on each side of a one-family dwelling shall be equal to 10% of the amount of the foot frontage of the lot, but in no event shall be less than five feet. Side yards on corner lots shall be 15 feet clear of all encroachments on the street side. Side yard fences are allowed to sit on side yard property lines.