But there is another factor that has dramatically increased the risk of collapse, according to L&I Commissioner David Perri: Developers are now cramming bigger buildings and more units onto rowhouse-sized sites. Single-family homes become duplexes, triplexes, even quad-plexes. Although it sometimes feels like the whole city is a construction site, most of this new housing is concentrated in just a few highly desirable neighborhoods. As the supply of infill sites in those places shrinks, land prices have soared. Developers now feel they must use every available inch of their property to maximize their return.