Mechanical floor

They are present in all tall buildings, including the world's tallest skyscrapers, with significant structural, mechanical and aesthetics concerns.

A consequence of this is that if the topmost mechanical floors are counted in the total, there can be no such thing as a true "top-floor office" in a skyscraper with this design.

Besides structural support and elevator management, the primary purpose of mechanical floors is services to house heating, ventilation, and air conditioning (HVAC) equipment.

[2] They may contain air handling units, cooling towers (in mechanical penthouses), electrical generators, chiller plants, and water pumps.

The pumps on each group of mechanical floors act as a relay to the next one up, while the tanks hold water in reserve for normal and emergency use.

Special care is taken towards fire safety on mechanical floors that contain generators, compressors, and elevator machine rooms, since oil is used as either a fuel or lubricant in those elements.

Most mechanical floors require external vents or louvers for ventilation and heat rejection along most or all of their perimeter, precluding the use of glass windows.

In this case, the ventilation systems of the mechanical floor are seen as gable vents, dormers, or abat-sons (louvers in a bell tower).

Mechanical attic (fourth floor) in Moore Hall at UCLA
A 60-story building under construction in Shanghai . The truss sections (made of triangular struts) will house mechanical floors.
The former World Trade Center twin towers. The "dark bands" were vents for the mechanical floors.
Mechanical equipment (elevator engine, cooling tower, and boiler) serving a high rise condominium, concealed within a decorative concrete enclosure to match the exterior of building
The mechanical penthouse (housing HVAC machinery) of Dodd Hall at UCLA is seen disguised as a bell tower with louvers provided for ventilation.
Dodd Hall mechanical penthouse as seen inside. Louvers are on the opposite wall.