In 30-plus years as a house mover in the San Francisco Bay Area, Phil Joy has accomplished some impressive feats. He once dragged a three-story Victorian several miles overland from Napa, Calif., to the water, then floated the house by barge down to the town of Benicia and set the building down on a new foundation. For moves through narrow streets with overhanging obstructions in Berkeley and Oakland, Joy has sliced houses in half—sometimes vertically and sometimes horizontally—and then spliced them together again when he reached the destination.
But some house lifts are just that: lifts. Tens of thousands of old wood-framed houses in the Bay Area were built with their first floors raised on short cripple walls set on shallow concrete footings. In earthquakes, failure of these cripple walls is common—enough so that reinforcing cripple walls against lateral forces is a whole niche of its own in the San Francisco market. (JLC has covered cripple-wall reinforcement before: see “Seismic Retrofit for Cripple Walls,” Apr/06.)
But it doesn’t take an earthquake for some cripple walls to fail. Recently, Joy has been called to lift two houses for which cripple walls had collapsed, seemingly without provocation. In one case, in Oakland, the house was vacant after the owners had passed away; while the family was deciding how to handle the building, it simple toppled off its cripple wall in the middle of the night.
In another case, in Berkeley, the homeowner was at home watching television when he felt the house slip and heard the wrenching noise of gutters and underfloor plumbing giving way. Suddenly, he found himself taking an unplanned elevator ride: In a few seconds, the house shifted over
3 feet and fell 3 feet, crushing utility pipes and underfloor equipment against the ground. In each case, the owners called Phil Joy.
“Right now it seems like we’re having an epidemic of hundred-year-old buildings falling down,” Joy told JLC in an email. “This is due to flawed underfloor framing. The buildings typically have redwood V-rustic siding on the lower 3 feet. They don’t have plywood sheathing. The V-rustic siding below the floor line doesn’t have much shear capacity to begin with, and the redwood rusts the nails. So when the nails rust, the houses have a tendency to lean over and slowly fall down.”
Lifting a house that has fallen off its cripple wall is challenging, Joy told JLC. “There’s no way to get beams under the house, since it’s on the ground. But we developed a process where we put 8-inch angle irons on the side of the building under the floor joist, and rock up one side with our hydraulic step jacks. After we rock up one side, we install a steel beam about 4 feet in from the side of the building.”
Beam location is determined by the floor-joist size and the weight of the building, Joy said (after decades in the industry, he has a feel for how a building will balance). “If the beams are too far in under the building, it will sag on the outside; if the beams are too far out, it will sag in the middle; if the beams are in the right position, everything is perfectly straight.”
Once he has one side of the building levered up off the ground, said Joy, “we start the process on the other side: rock the building up, and put in another steel beam. Now that we have two steel beams underneath the building, we hook up to the unified jacking machine and raise it straight up, and then roll it back over the foundation on rollers.”
No two houses fall in the same direction, Joy said, so re-aligning each house with its foundation is an art. Homes often have to be pivoted, which requires the rollers to be placed in a radial fan configuration that lets the house spin as well as move laterally.
When the house is up off the ground and properly aligned, a foundation contractor can come in to replace the concrete footings, and a framing contractor can rebuild the cripple walls. The new work, of course, is typically superior to the original failed structure: Current seismic codes require engineered footings and cripple walls capable of withstanding earthquake forces.