An Old House Gets a New Thermomass Basement
After jacking up this house in Cambridge, Massachusetts, we installed a new energy-efficient foundation
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 asbestosMineral fiber once commonly used in many building materials, including insulation, fireproof siding, and resilient flooring. Inhalation of invisible asbestos fibers can lead to chest and abdominal cancers as well as scarring of the lungs. The use of asbestos in some products has been banned by the EPA and the U.S. Consumer Products Safety Commission; manufacturers also have adopted voluntary limitations on its use. When found in older buildings (most commonly in floor tiles, pipe and furnace insulation, or asbestos shingles), the product's friability is a major determinant in how it must be handled during renovations. More information: http://www.epa.gov/iaq/asbestos.html 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 ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. 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 capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. 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 (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) 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.
- All photos: Brian Butler
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