Signal House is a missing middle prototype addressing the nation’s shortage of attainable urban housing. The single-stair, walk-up infill building, located less than a block from a key transit hub in Philadelphia’s Fishtown neighborhood, fits three units on a modest lot that would more typically be slated for use as a single-family rowhome. An interlocking organization incorporates mezzanine levels and bi-level unit layouts, going vertical as a way to add square footage and livability as well as light, air and views on an otherwise landlocked parcel.

An infill triplex layout is typically limited by access to light and air at the front and rear, with middle and lower units further compromised by subtracted space for common circulation. Signal House’s small footprint was expanded with a strategic approach to the building section, using mezzanines to create bi-levels and bay projections to increase unit areas. Bonus flex spaces were added in the lower two units, and the additional height afforded by extra levels pushed the building above its neighbors, offering 360 degree skyline views over adjacent structures.

The building’s single-stair, walk-up typology is designed to maximize habitable space on its small, transit-adjacent site. Instead of placing a luxury rowhouse for a single family on the lot, the client – a local housing developer builder looking to add value across a series of small parcels – elected to create three multi-level units sized to accommodate families or cohabitating singles. Within its three units, the building provides a total of eight private and semi-private rooms for singles, couples or families to sleep and work, creating dwelling opportunities for many more people than a single-family home. The building’s larger yet tightly organized unit layouts allow residents to share common space and infrastructure while maintaining privacy, making for an efficient and replicable model for high-density urban housing.