Height limits shall not apply to church spires, belfries, cupolas, or domes not used for human habitation, nor to chimneys, ventilators, skylights, parapet walls, cornices, solar energy systems, or necessary mechanical appurtenances usually located on the roof level, provided that no such appurtenance, other than a church spire or the tower of a public building, shall exceed 10 feet in height. No such uses shall in their aggregate coverage occupy more than 10% of the roof area on which the use is located.