A three-decker, triple-decker triplex or stacked triplex, in the United States, is a 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 an economical 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. 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. History Three-deckers were most commonly built in the emerging industrial cities of central New England between 1870 and 1920. There are large concentrations in Massachusetts and Rhode Island. Worcester, Massachusetts, was the likely origin of the type, with Francis Gallagher (1830–1911) held to be the originator. Other cities make the same claim, and they can also be found in the former industrial cities of New Hampshire, Maine, and Connecticut, as well as the New York City area (particularly in northern New Jersey and Yonkers) and Upstate New York, where they are commonly seen as far west as Utica. Three-deckers are also found in Canadian cities with strong ties to New England, particularly Halifax, though they are less ubiquitous. They were primarily housing for the working-class and middle-class families, often in multiple rows on narrow lots in the areas surrounding the factories. They were derided as poor-quality buildings, shoddily constructed from flammable balloon framing: a 1911 report by the Massachusetts State Housing Committee in Massachusetts decried the three-decker as "a flimsy fire-trap and a menace to human life". It is estimated that by 1920, the city of Boston had over 15,000 three-decker houses. Areas such as Dorchester, Roxbury, Mattapan, and Jamaica Plain were popular with the emerging middle class and became "streetcar suburbs" as transportation systems expanded from the older, core sections of the city. Typically, the affordable three-decker homes attracted live-in landlords who would collect rent from the other two apartments. In Worcester, Massachusetts, sewer