After replacing the damaged cast-iron sewer pipe with PVC, we filled the excavated area below the old garage slab with crushed stone, applied in lifts and thoroughly compacted with a plate compactor. A new frost wall was also poured at the front of the garage.
In addition to pouring a new garage slab, we poured a second slab in the new crawlspace, and provided access by cutting an opening from the adjoining basement with a concrete ring saw (Figure 8). The masons also built two short support walls beneath the cantilevered hearth extension, adding a steel column at the one unsupported corner for good measure.
The new floor system above the crawlspace was framed with I-joists. At the garage end, they sit on the new garage wall and are closed off with a pressure-treated lumber header; at the other end they’re supported by top-mounted joist hangers and a ledger fastened to the original perimeter wall.
All of the structural work was completed in approximately three weeks, with the remaining carpentry and finish work taking three additional weeks. The owners were very happy with the results.
Mark Reinmiller, P.E., is a structural engineer in Lansdale, Pa.