Three-decker (house)

A three-decker is the U.S. term for a type of vertical triplex apartment building. These detached three-story buildings are typically of light-framed, wood construction, where each floor usually consists of a single apartment. 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 region’s factories. A typical tree-decker contained three apartments, usually with identical floor plans.^[1] The three-decker apartment house was seen as an alternative to narrow single-unit row-housing built in other cities of Northeastern United States during this period, such as New York City, Boston, Philadelphia, Baltimore, and Washington, D.C.

Originally, extended families often lived in two or all three floors. Some three-deckers were divided into six units.

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