Three-decker (house)

A three-decker, in the United States, is a type of three-story (triplex) apartment building. These buildings are typically of light-framed, wood construction, where each floor usually consists of a single apartment, and frequently, originally, extended families lived in two, or all three floors. Both stand-alone and semi-detached versions are common.

During the late 19th and early 20th centuries, tens of thousands of three-deckers were constructed, mostly in New England, as a cheap means of housing the thousands of newly arrived immigrant workers who filled the factories of the area. The economics of the three-decker are simple: the cost of the land, basement and roof are spread among three or six apartments, which typically have identical floor plans.^[1] The three-decker apartment house was seen as an alternative to the row-housing built in other cities of Northeastern United States during this period, such as in New York City, Boston, Philadelphia, Baltimore, and Washington, D.C.

Three deckers often account for a disproportionate number of structure fires.^[2]