Back at the turn of the 20th century, miners flocked to the new town of Louisville, Colo., to work in its emerging coal industry. There must have been some skilled carpenters among them, because the town is filled with beautiful Victorian-era homes. Unfortunately, they built the foundations the same way they built coal mines, driving wood pilings into the ground and framing right on top of them. Over the years, those old wood foundations have failed and been replaced with a hodgepodge of stone, concrete, and block, none of which is particularly well-suited for the area's expansive clay soils.
Such was the history of my clients' house: The shallow spread-footing foundation that replaced the original perimeter pilings had settled over the years, causing the wood floors of the foursquare home to sag, buckle, and splinter.
When one of those splinters lodged in their daughter's foot, my clients decided it was time to contact an engineer, who proposed replacing the entire ground-level floor system with a new one supported by helical piers (see illustration). The piers and new LVL floor framing would also support the wall framing and roof loads; the old concrete foundation would remain in place, but it would no longer serve any structural purpose. I was hired because I was the only builder bidding the job who suggested that this would also be a good time to improve the home's energy performance by air-sealing and insulating the new framing.
Demolition
Our goal was to stabilize the foundation and flatten the floor, but not necessarily to level the house, since jacking the walls could damage the home's old plaster finishes. My clients briefly considered raising the house and adding a full basement, but decided they didn't need the additional space. A previously built basement-level masonry-block mechanical space would remain.
We started by removing as much of the floor system as we could while leaving the perimeter walls and existing foundation intact (see slideshow). There was no subfloor, so we stripped the wood flooring and began removing individual joists. The walls were balloon-framed, which simplified the process of removing the joists along the exterior walls. We left short sections of the joists in place under the center bearing wall, which we temporarily shored. Then we called in the helical pier contractor.
Helical Piers
Helical piers are a cost-effective way of dealing with the expansive clay common in this part of Colorado. While the piers often have to be driven fairly deep to support the loads, the process requires no excavation (for more about helical piers, see "Building a Freestanding Deck," 12/11; "Stabilizing a Hillside Foundation," 12/11; and Letters, 3/12).
Piers are typically sized according to the soil's type and bearing capacity. On this job, the engineer specified 6-inch-diameter single-helix lead sections with 1-1/2-inch square shafts. Extensions were added until the bearing plates were about 30 feet below grade, where the torque readout on the driver met the design loads. On most of our jobs, the contractor mounts the hydraulic auger on a skid-steer or a mini-excavator; in this case, he connected a hand-held driver to the takeoff on the excavator so the piers could be installed from inside the building. It took about a day to lay out and drive the 10 piers needed on this project, and another couple of days to cut off the steel extensions, weld on cap plates, and pour short 10-inch-diameter Sonotube piers at the top. Each pier was topped with an 8-inch-by-8-inch-by-1/4-inch steel plate set into the wet concrete.
