A mechanical penthouse is a floor level holding mechanical equipment, which is positioned above the regular floors of a building, and which is set back from the building's perimeter. When a mechanical penthouse is present, a building usually (but not always) has a flat roof with boxes.

The most common purpose of a mechanical penthouse is to hold the sheaves and engines for traction elevators. In these cases it is often called an "elevator penthouse". However the terms are not synonymous, as mechanical penthouses frequently hold fan rooms and other mechanical equipment.

The need for a mechanical penthouse can be eliminated in tall buildings by the use of machine roomless elevators.