From Philly Brownstoner: "Dubbed the London House, indicating a popular plan found at the time in England’s capital...these rowhouses were constructed for speculative housing as the city’s population grew and a real estate was a chief investment opportunity. Not only were these houses suitable for residential use, many of the colonial and federal city’s artisan shopkeepers operated their businesses out of the first floors of this rowhouse form. The London House is generally 15–18 feet wide, 3 ½ stories high and constructed of brick with a gable or gambrel roof and a single dormer. The front façade has two bays of sash windows with limestone lintels and sills. The first floor entrance was again raised a few steps from street level, often only adorned with simple woodwork, paneling and a transom window. Entrance into the interior leads either to a side hallway, as in the townhouse or to a front room the full width of the house, as in a trinity." Full article here.