No outside fire escape or other outside structural addition projecting from a building over a public alley or thoroughfare shall be erected without first securing a permit from the building inspector or his authorized agent. The building inspector or his authorized agent shall not issue a permit for the building of such outside fire escape or other structural addition unless the plans provide for a complete minimum twelve foot six inch (12'6") clearance in height from the permanently established grade of the alley or thoroughfare below, provided that where such grade has not been established, the clearance shall be on the basis of the proposed grade for such alley or thoroughfare as set by the building inspector. (1975 Code Ch. 16 § XXII)