Accessory buildings which are not a part of the main building may be built in a rear yard in the "C-1" District when such yard abuts a residential district. An accessory building which is not a part of the main building shall not infringe into the required yard more than one hundred twenty-five (125) square feet.

Every part of a required yard shall be open to the sky, unobstructed, except for accessory buildings in a rear yard, and except for the ordinary projections of skylights, sills, belt courses, continuous sills, cornices and ornamental features projecting not more than twelve (12) inches. This requirement shall not prevent the construction of fences, except within the required front yard.

Open or lattice-enclosed fire escapes, fireproof outside stairways, balconies opening upon fire towers projecting into a yard not more than five (5) feet, and the ordinary projections of chimneys and flues may be permitted.

An open unenclosed porch not more than one (1) story in height or a paved terrace may project into the required front yard for a distance not exceeding ten (10) feet. An enclosed vestibule containing not more than forty (40) square feet may project into the required front yard for a distance not to exceed four (4) feet.

Terraces, uncovered porches, platforms and ornamental features which do not extend more than three (3) feet above the floor level of the first (ground) story may project into a required yard, provided these projections be distant at least two (2) feet from the adjacent side lot line.

Where a lot or tract is used for a commercial purpose, more than one (1) main building may be located upon the lot or tract, but only when such buildings conform to all open space requirements around the lot for the district in which it is located.

When forty percent (40%) of a frontage is developed with two (2) or more buildings, then the depth of the front yards heretofore established shall be determined by a line drawn from the closest front corners of two (2) adjacent buildings.