XS House

Architecture Firm(s): ISA

Owner: Callahan Ward

Location: Philadelphia, Pennsylvania

Category: Up to $1.5 million in construction cost (category two)


Built on a plot of land so small it barely registered as a development parcel, this project added seven apartments to Philadelphia’s Chinatown neighborhood on a site measuring just 11 feet by 93 feet. In addition to rejuvenating an overlooked site, XS House serves as a prototype for urban living through the maximization of density. While housing markets continue to boom and lots become more and more scarce, this project proves that even the smallest projects possess the potential for significant impact.

XS House’s roots are tied to Philadelphia’s urban renewal, during which the sunken Vine Street Expressway left a 100-foot east-west rift through a number of neighborhoods, Chinatown included. Disconnected by the construction, Chinatown saw many of its blocks chopped up into awkward and odd-shaped parcels, many of which became surface parking lots. This project radically rejuvenates one of these sites, boosting street life and supporting walkable lifestyles in a neighborhood bereft of them.

“XS House is an amazing project, one that could serve as a model for the many undeveloped small parcels in our urban areas.” - Jury comment

The team expanded the extremely narrow footprint through the clever use of bays and mezzanines. Though it is a four-story building, the project connects seven levels of occupied space and features unit stairs that lead to private mezzanine levels and create dramatic volumes. A single shared stair runs through the center of the building and provides access to the upper units, while the lower units can be accessed at street level.

The design team partnered with a private developer interested in multi-family housing projects on underused land. By choosing the narrow site, the client was able to invest in high quality building elements while keeping rents reasonable. The team, through its transparent process, balanced constraints with a range of design options to allow the client to make the best decisions for the site and surrounding community.

“If we are ever to achieve equity, and fight climate change, we need architectural solutions like this—that let us do more with less—converting one small parking lot into seven beautiful, effective housing units.” - Jury comment

Additional information

Engineer - Structural: Larsen & Landis Structural Engineers

Engineer - MEP: J+M Engineering

General Contractor: Callahan Ward

Photographer: Sam Oberter

Lighting: Lam Partners


Melissa Harlan, AIA (Jury Chair), Christner Inc., St. Louis, MO

Mark English, AIA, Mark English Architects, San Francisco, CA

Meryati Blackwell, AIA, ASID, LEED, Marlon Blackwell Architects, Fayetteville, AR

Upali Nanda, PhD, HKS Research | Faculty Taubman U Mich., Ann Arbor, MI

Brian Korte, AIA, Clayton & Little, San Antonio, TX

Image credits

XS House

Sam Oberter

XS House


XS House

Sam Oberter

XS House

Sam Oberter

XS House

Sam Oberter