Replacing a Foundation and Retrofitting a First Floor

Framing

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Around the perimeter of the building, a specialty subcontractor … Read More Around the perimeter of the building, a specialty subcontractor installed helical piers as close to the foundation walls as practical. Given the region's expansive clay soils, the lead helix was driven to a depth of around 30 feet.

Each pier was topped with a steel-reinforced concrete pier; a st… Read More Each pier was topped with a steel-reinforced concrete pier; a steel bearing plate was embedded in the wet concrete at exact finish height.

LVL ledgers attached to the exterior wall studs with structural … Read More LVL ledgers attached to the exterior wall studs with structural screws provided a means of support as the sill was removed and the steel beam maneuvered into place.

Emplacement of the steel beam

At the center bearing wall, the crew had to work around the temp… Read More At the center bearing wall, the crew had to work around the temporary supports under the short joist remnants as the steel was inserted.

To make this process easier, the beam was fabricated in sections… Read More To make this process easier, the beam was fabricated in sections designed to be bolted together on site.

Working a wall section at a time, the crew cut the studs off and… Read More Working a wall section at a time, the crew cut the studs off and extended them to the new girder under the bearing wall.

Along the outside walls, a double rim was installed from outside… Read More Along the outside walls, a double rim was installed from outside at the same elevation as the original sill.

Upside-down joist hangers help transfer roof loads to the new st… Read More Upside-down joist hangers help transfer roof loads to the new steel beam.

A heavy vapor retarder will help keep the crawlspace dry.

Before we could remove the old sills and start reframing the floor, we had to support the exterior walls. To do this, we bolted LVL ledgers around the perimeter of the building using structurally rated hex-head screws, two screws to a stud (see slideshow). We then laid doubled 2-by plates on the ground and cut 4×4 posts to fit snugly between the plates and the ledgers on 12-inch centers. With the building thus supported, we removed the old sills a section at a time and began cutting off the bottoms of the studs to a level line that we had marked with a laser.

Steel girders. We installed three steel girders, capped with wood plates, to support the new floor framing. The I-beams were fabricated in sections designed to be bolted together, since getting a full-length beam would have been impossible, given the constraints of the site. Even so, this was one of the most difficult parts of the job. Sliding the steel underneath the center bearing wall was particularly tricky, because we had to do so without disturbing the temporary supports under those short joist remnants. After the steel beams were in place, we had them welded to the cap plates on the helical piers.

LVL joists. Next, we removed enough plaster and lath from the bases of the bearing walls to expose about 18 inches of framing. We then carefully extended the studs down to the girders, a stud at a time, pulling the temporary supports as we went and sliding the new LVL joists into position, 12-inches on-center. We used metal shims to bring each joist up to our benchmark elevation, then toenailed them to the plates. Later, we reinforced the connections with metal connectors. Finally, we fastened doubled pressure-treated 2-by rims to the floor joists, reinforcing the connection with upside-down joist hangers, per the engineer’s instructions.

Moisture Control and Air-Sealing

Before sheathing the floor, we installed a 6-mil plastic vapor barrier across the ground and up onto the rim joists, overlapping and taping the seams. Our insulation sub sealed the rims with open-cell spray foam. After installing new ductwork, we laid new floor sheathing and continued with what, at that point, became a standard renovation. Total project cost was about $90,000, which included all of the structural work, new finishes, and a new high-efficiency direct-vent water heater.

Clay Dusel is a builder in Boulder, Colo.