A dryer atop a washing machine
stacked clothes dryer
A style of clothes dryer designed to save space by either being stacked atop or built atop another clothes dryer or a washing machine. Units composed of two dryers stacked one on the other is a common feature of laundromats. For homes with limited space a dryer unit atop a washing machine, known as a laundry center or laundry tower, is also common.
Washing machines normally aren't stacked due to the additional weight and force of the moving water while in operation and are always the bottom unit of a laundry tower or stacked washer and dryer pair.