No single-family residence built or existing in this district shall have a height greater than 40 feet from the grade abutting the structure on the front side of the structure. For purposes of this subsection, the height of the building shall include the highest roof point of any interior portion of the structure which can be occupied, including, but not limited to, attic and storage structures and observatories which accommodate entry or occupancy by a person, but shall not include roof attachments such as chimneys, antennas or decorative cupolas.