Image Credit: All photos: Brian Butler Steel beams were slid under the floor joists to support the house while it was being jacked up. Once the jacking process was complete, the house was supported by temporary cribbing. A passerby observes the demolition of the old foundation walls. To prevent the wicking of moisture from the damp footing to the wall above, a strip of rubberized asphalt membrane was installed on top of the footing as a capillary break. The XPS insulation panels that are inserted into the Thermomass walls are equipped with fiberglass pins that keep the insulation centered in the concrete wall. Forms have been erected for the new Thermomass walls. After the foundation forms were stripped the cross-section of the completed Thermomass sandwich was apparent.
To prepare our bid for a comprehensive renovation project in Cambridge, Massachusetts, we visited the old house several times. On one of the walk-throughs, we realized that the foundation was failing in many places. We therefore proposed to raise the house and replace the entire foundation.
Raising this house was a challenging process, given the tight space and the existing condition of the house.
The house was jacked up 3 feet
We first finished all the interior demolition and removed the existing asbestos siding on the building. We then demolished the concrete slab in the basement and dug pits for the cribbing stacks to sit on. We also added new joist hangers and sistered and shored several floor joists to ensure structural stability.
Steel beams were slid under the house from front to back (see Image #2, below), and high-powered hydraulic jacks slowly raised the structure about 3 feet off its foundation, providing enough room for demolition crews and equipment to pass under the structure.
All of the existing foundation walls were then demolished (see Image #4) to make way for a new insulated poured concrete foundation and a modern drainage system.
Concrete foundation walls hide a foam filling
We used the Thermomass system for the new foundation walls. A Thermomass wall creates a sandwich with two layers of concrete enclosing a filling of rigid foam insulation. (A Thermomass wall is the inverse of an ICF wall.) The insulation in a Thermomass wall creates an excellent thermal break between the earth and the interior.
We started by installing a bituthene membrane on top of the concrete footing to create a capillary break between the footing and the wall (see Image #5).
Then the concrete contractor drilled steel dowels into the footing to anchor the wall. The next step was to set up the 4-inch-thick (R-20) extruded polystyrene (XPS) foam panels. These panels have fiberglass dowels that help keep the panel perfectly centered in the concrete form (see Image #6).
Then the concrete wall forms were erected. Finally, a concrete pump truck showed up to place the concrete. After a couple days, the forms were stripped and ready for dampproofing and backfill (see Image #8).
Better than new
Once the new foundation walls were installed, we set the house down, removed the cribbing stacks, and poured a new insulated basement slab before framing for new interior partitions.
This job was a great opportunity to save a little piece of Cambridge’s historical past. The home got a new lease on life, and will provide thermal comfort that is better than a code-built new-construction home.
Brian Butler is a production manager at Savilonis Construction Corporation in Natick, Massachusetts.