definition
strict definition
exposed machinery
Exposed mechanical equipment installed at a structure's top and forming its highest physical element.
Exposed machinery refers to any sort of mechanical equipment which is installed at the top of a structure, and forms the highest element of that structure.
The equipment must be both at the top and uppermost to provide this tip element. Machinery installed lower on the structure does not set that highest point.
Its role is mechanical rather than an architectural adornment. The architectural top element separately identifies the highest feature belonging to the building's design.