Constructing a basement using precast foundation walls includes preparing the gravel base, placing and connecting the panels, installing a capillary break, installing the flooring, and backfilling.

After the site is excavated and the perimeter drain is laid, a bed of clean, compacted gravel is distributed over the perimeter drain. The gravel facilitates sub-slab drainage; water drains down the panels, through the gravel bed, and into the perimeter drain system. The gravel also transfers the load from the foundation wall to the surrounding soil. The gravel layer will be 4" to 12" thick, as determined by a soils engineer, to meet the foundation’s load-bearing needs.

Next, a crane is used to place the first concrete panel. It’s braced, and a second panel is placed to form a corner. The joint is sealed with a urethane sealant, and the panels are bolted together. Additional panels are placed in the same fashion, usually without needing any bracing. All corner joints are mitered, and all other joints butt together. Once all panels are placed, sealed, and bolted, any code-required waterproofing is applied.

Third, a 4" to 6" layer of gravel is spread over the slab footprint. A 10-mil vapor barrier is installed on top of the gravel layer, covering the entire footprint of the foundation. Together, these form a capillary break between moisture in the soil and the underside of the basement slab.

Finally, the basement slab is poured, and floor joists are installed above the foundation. Both of these provide bracing for the foundation walls before backfilling begins—the concrete slab anchors the bottom and the floor framing locks the top. The foundation is then backfilled and can be considered complete.

Builders are taking advantage of the many benefits precast foundation walls offer. Installing a precast system can speed construction, as well as help to ensure that your customers enjoy a dry, comfortable basement.

For more information about precast foundation walls, review our related article “Casting the Vote for Precast Walls.” Other Best Practices® for foundation construction can be found in the following online training courses from BuildIQ University:

• Foundations: Slab-on-Grade
• Foundations: Basements & Crawlspaces
• Water Management: Slab-on-Grade Foundations
• Water Management: Basements & Crawlspaces