Height Limits. Penthouses or roof structures for the housing of stairways, tanks, ventilating fans, air conditioning or similar equipment required for the operation and maintenance of the building, skylights, spires, cupolas, flagpoles, chimneys or similar structures associated with buildings in the HC, NC, REO-1, REO-2, REO-3 and MFG Districts may be erected above the height limits prescribed by this chapter, but in no case more than 20% more than the maximum height permitted for the use in the district. Chimneys on residential dwellings and silos and barns associated with farming shall have no height restrictions.