A mechanical floor is a floor level above ground which is occupied by mechanical equipment, and which is not set back from the perimeter at the top of a building. Mechanical floors below ground level count as basement floors, not mechanical floors. If the floor is set back from the building perimeter at the top, it is classified as a mechanical penthouse.

Mechanical equipment includes heating, air conditioning, ventilation, elevator operation, fire protection, window washing, water storage, plumbing, electrical systems, and communications hardware.

Above-ground position and the relationship to the top perimeter distinguish the category. A recessed top-level equipment floor is a mechanical penthouse, while an underground equipment level counts as a basement.