From Philly History writer Ken Finkel: "Philadelphia’s most effective tool in its industrial transformation during the late 19th century wasn’t a tool at all, although it could be considered a machine for living. As architectural historian George Thomas put it, the rowhouse was 'the quintessential object of Industrial Philadelphia.' "But the Philadelphia rowhouse had far older roots. In 1800, Scottish-born 'architect and house-carpenter' Thomas Carstairs took the idea of a row and stretched it out for a full city block on Sansom between 7th and 8th Street. Over the next several decades, as the city grew across its 17th-century grid, the rowhouse evolved into an upscale solution for urban living.
"But as the city’s population soared past one million in 1890, the rowhouse was effectively reclaimed for the working class. Between 1887 and 1893, no fewer than 50,288 rowhouses were built, enough for a quarter million people. With the help Philadelphia’s 450 savings and loan associations, a two-story 'Workingman’s House', as it became known, could be had for about $3,000 and paid off in about a decade.
"The Philadelphia model was more than a mere solution to a housing problem; it became an effective tool for a modern society. 'The two-story dwellings of this city are, beyond all question, the best, as a system, not only owing to the single family ideas they represent, but because their cost is within the reach of all who desire to own their own homes,' glowed a rowhouse proponent in the early 1890s." Full post here.