L&I declared both collapsed homes "imminently dangerous." A demolition crew hired by L&I began tearing down both Monday evening as the contractors also worked to remove as many of the residents' personal items as they safely could. The Palmer Construction crew has a month to finish the $38,000 job, officials added, noting that the homeowners must repay the city for the demolition.
Generally, Williams said, even one loose or missing stone in a rubble wall - which can get dislodged as mortar surrounding it gradually deteriorates to dust - may lead to a collapse.
"The mortar deteriorates over time and loosens up the stone," he said. "Then the rest of the structure that sits on the foundation ultimately is compromised, and [here], it collapsed."
In modern building, Williams said, rubble walls and mortar are rarely used. Instead, he said, typical foundations are "a continuous slab" of concrete.
Williams has said that if any resident of 6015 or 6017 Spruce had been home, the collapse could have been life-threatening. All the occupants had left for the day, and no injuries were reported.
One of those occupants was Christine Chapman, the owner of 6017 Spruce for 33 years, who said Tuesday that she was taking things "hour to hour - not even day to day."
"I'm basically numb," said Chapman, 62, a veterinarian technician who lived with her two 100-pound Scottish deerhounds. Chapman said she was at work at the University of Pennsylvania when her home caved in.
A self-described pragmatist, she said, "Good things happen, bad things happen - you just hope the good ones outweigh the bad ones, but sometimes they don't."
Chapman described rushing from work in a desperate search for her dogs, Duncan and Brie. Duncan had escaped the backyard and was roaming the neighborhood, but police were able to corral him safely. Brie, uninjured, was still inside the home. A Red Paw Emergency Relief Team member helped Chapman retrieve the frightened dog.
Chapman, who is staying with her son, said the dogs are "stressed, but they're depending on me, and to be honest, I'm depending on them."
Williams noted Tuesday that many homes in the Northeastern United States were built with rubble stone and mortar foundations. He and L&I Emergency Services Director Scott Mulderig said anyone with turn-of-the-century or early-1900s homes should check basements at least yearly for loose or missing rubble stone; a dusty or sandlike buildup of deteriorated mortar; or water that could signal a compromised foundation or wall.
City residents who see those signs should ask L&I to inspect, Mulderig said.
In a statement released Tuesday, L&I said that after the collapse, it inspected 42 properties on the 6000 block of Spruce and, aside from signs of water infiltration, found no structural concerns. Inspectors were to attempt entry to five remaining houses later Tuesday, L&I said.