This Philadelphia Inquirer article is behind a paywall, but I can tell you that it speaks to the city's increasing use of modular construction for infill apartment buildings:

Building modularly can save 20% on total construction costs, he said. Projects can be constructed in half the time, and rental revenue comes in sooner. Workers build apartments in pieces in a factory as others lay the foundation. Factory work doesn’t have to pause for inclement weather.

Alterra Property Group has found that modular construction is cost- and time-effective when it builds between 100 and 500 units and between four and six stories. Under that, building on-site is more efficient, Addimando said. Above that, builders can run up against building code restrictions.

Consider this recently completed project, called LVL North:

• 1.5 acre site

• Site acquired in February 2020

• Construction commenced in June 2020 (was it already entitled?)

• Over 500,000 square feet

• 7 storeys

• 410 market-rate apartments

• Two levels of commercial spaces

• Over 300 parking spaces in a two-level below-grade parking structure

• Construction completed in 24 months (it's currently being leased up)

I am impressed by how quickly this was erected. Here in Toronto, it would likely take more than 24 months just to get through the rezoning process. Granted, a site this big in a central location next to transit would also likely beget multiple tall buildings.

But this form and scale of housing seems to be working for Philly. It is allowing the city to both build quickly and to experiment with emerging construction methods.