A former Center City Philadelphia office building has officially reopened as a 176-unit apartment community. The residential conversion at 400 Market Street reached 40% leased before welcoming its first residents.
West Conshohocken-based Keystone and development partner Dean Adler completed the transformation of the nearly vacant office property. The first residents recently moved into the building, with additional leases scheduled to begin over the following months.
The developers acquired the 173,700-square-foot property for $10 million in June 2024. Previously, the building operated as an office property before declining occupancy created an opportunity for residential redevelopment.
Construction began in January 2025, allowing the developers to complete the conversion in approximately 15 months. The building’s limited remaining office tenancy helped accelerate the redevelopment process.
The project includes significant interior improvements and new residential amenities. Residents have access to a renovated lobby, fitness center, lounge, package room, and 24-hour security desk.
Additionally, a 2,500-square-foot rooftop deck will feature a sauna, barbecue grills, fire pits, and recreational space. These amenities support the property’s transition from a traditional office building into a modern apartment community.
Originally constructed in 1970, the building features a distinctive Brutalist architectural design. Historic preservation requirements protected portions of the façade, original lobby flooring, and an existing sculpture.
The property’s approximately 15,500-square-foot floor plates also supported its conversion potential. Suitable building layouts can play an important role in determining whether older office properties can accommodate residential uses.
Notably, 400 Market Street joins a growing number of Center City office buildings transitioning into apartments. Changing workplace demand has encouraged developers to explore alternative uses for underperforming commercial properties.
For Philadelphia’s commercial real estate market, the project demonstrates how adaptive reuse can reposition existing buildings. Residential conversions can introduce new activity into properties that previously struggled to attract office tenants.
The building’s early leasing performance also suggests encouraging demand for its new residential offering. As additional residents move in, 400 Market Street represents another step in Center City’s evolving real estate landscape.
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