Piggyback washers and dryers, more frequently called stackable washers and dryers, place the dryer on top of the washer instead of next to it. These combination units save floor space, making them popular in apartments and other small structures.
Stackable washers and dryers let owners place both units in a relatively small closet or in a kitchen, saving valuable space. However, their vertical orientation means that the washer must be front-loaded, so items cannot be placed inside once it's filled with water. Dryers might be placed too high for some users. Repair costs might be a bit higher as well since the heavy dryer often has to be moved before it or the washer can be inspected and fixed.