Our design/build company performs a wide variety of building services. We're equipped to handle every aspect of new construction and remodeling, including house-lifting and foundation and septic-system installation, as well as framing and finish carpentry, all in-house.
In September we undertook the restoration and remodel of a two-story early-1800s residence in the historic village center of Wellfleet, Mass. We began by lifting the house off its failing foundation and setting it back down on a full poured-concrete basement. This article will look at that process. As of this writing, we've moved on to a gut-remodel of the building.
Existing Conditions
The house was built on a lot that sloped immediately down from street level, which set the front door sill about 9 inches lower than the sidewalk. Because no attempt had been made to adjust the grade to deflect runoff, water ponded against the foundation, eventually rotting the front sill beam. Also, the oldest part of the foundation consisted of a single thickness of mortared brick (common in the area's sandy soils) set barely below grade without any footings. Consequently, the building had settled unevenly, stressing its timber frame to near failure. When we started work, the building department had already ordered the house vacated.
At the back of the original building was an extension that had been built in the 1920s on a full foundation of hand-mixed concrete interlaced with bricks and rubble. This part of the foundation was accessible through a door in the rear and allowed about 6 feet of headroom. Under the original structure, the builders had expanded the basement area by excavating to within a few feet of the older brick foundation, shoring it with small-diameter logs driven vertically, stockade-style. This innovative approach may have destabilized the grade, and a small forest of teleposts suggested a history of nerve-racking creaks and pops as the building settled.
Digging In
The shifting foundation had caused some of the tenons in the timber balloon frame to pull away—as much as 1 1/2 inches in places—from their mortises. Before we jacked anything up or worked on the sills, we stabilized these joints by running a heavy chain from a central interior timber through the tops of the first-floor gable-end windows to a pair of 6x6s running the full width of the building. We used a come-along to keep tension on the chain, which prevented the frame from spreading further during the foundation work. (Later, after the building had been set down on its new foundation, we would pull the joints tight and reinforce the connections.)
The rotted front sill had to be addressed before we did anything else. We stripped back about 2 feet of siding and sheathing across the front of the building. To create room to stack cribbing, we hand-dug pocket holes about 4 feet deep, undercutting the foundation near the corners and at the center. After stacking the cribbing, we used bottle jacks to raise the building just enough to slide in short lengths of 6x6s directly under the existing sill.
With the front wall supported by cribbing, we started removing badly rotted portions of the sill. Very quickly we confirmed our suspicion that the sill was almost completely rotted through along most of its length and that it would be best to replace it entirely before attempting to lift the building. We pulled a string-line from corner to corner as a reference for straightening the sagging timber-frame system, then jacked and shimmed until the bottoms of the four posts—one at each corner and two on either side of the central door—registered uniformly against the string.
With the front wall timbers in plane, we bolted a 6x6 ledger to the face of the frame along the entire length of the building, pre-drilling the four 8x8 posts to receive 1/2-by-12-inch lag screws. We used TimberLoks and LedgerLoks to secure the 2x4 infill studs, many of which did not run the whole length of the balloon frame and were supported by the sheathing. Then we set jacks on the cribbing and lifted the ledger to shift the weight of the structure off the sill, enabling us to remove it and fit a new, pressure-treated 6x6 member in its place. Including the stripping of the siding and sheathing, this process took a full two days.
Setting Steel
With the front sill replaced, we turned our attention to placing the steel I-beams needed for the lift. Since the building itself occupies most of this street-corner lot, access for inserting the beams was limited to the back, where we had a small staging area, and one side of the building at the front (see "Beam Layout/Foundation Plan"). Given the close quarters, we delivered mainly 16-foot lengths of steel, which we welded on site to create the lengths we needed.
One of the design principles for lifting a beam is that its flange should be at least as wide as the web is high—nominally, a square section profile that prevents the beam from rolling over under load. This was a particularly important consideration for the two main beams, which would provide the direct jacking points for lifting. These two beams would need to be 50 feet long and would run outside the walls of the building's narrower rear extension and under the original structure at front. We built them up from front to back using W12x35 I-beams welded side-by-side with their ends offset in a staggered pattern. Each 16-foot section weighed about 560 pounds, so we used our mini-excavator to wrestle them individually onto cribbing before welding.
We wanted to set the beams as near to their final elevation as possible so we wouldn't have to lift them very much later. Fortunately, the halfway point on these beams fell outside the foundation, so we were able to move them nearly into final position without having to reset the support straps that suspended them from the excavator. We set them level, at a height that left enough room for the shorter crossing members to fit between them and the underside of the floor framing. This sounds more straightforward than it actually was because we had to set up temporary cribbing stations at various locations under the front part of the building to support it while we excavated access points for the main beams through the old foundation. Ultimately, each of the two main beams rested on four cribbing stacks, two inside the foundation at the front and two outside the foundation along the rear addition.
Next, we inserted the "needles," or crossing beams, from which we would ultimately block up to support crucial locations under the building. In the addition, the joists ran across the width of the building and were mortised into a central carrying beam. We placed four needles parallel to the joists, shimming as needed to pick up the central timber and to make sure that all three sills in the addition were fully supported.
