Footings, Foundations, and Slabs Review

This lesson identifies the foundation types ICFs are built on, the advantages of each, and the basics of squaring an ICF project.

Before selecting a foundation, BuildBlock strongly recommends consulting a local structural engineer or contractor familiar with your region’s soil load-bearing capacity. Footings are a shallow foundation that distributes the structure’s loads directly to the ground. Deep foundations carry loads farther down: concrete piers are drilled to an approved diameter, depth, and spacing, then filled with rebar and concrete, and are used for very heavy buildings or weak surface soils. Grade beams—reinforced concrete that transfers a bearing wall’s load to spaced supports like pile caps, caissons, or piers—can sit on piers when surface soil is weak, or be used alone when soil capacity exceeds the design load. Slab-on-grade foundations are formed and set directly on the ground, sometimes post-tensioned or with thickened edges to support the ICF forms. Size the foundation using prescriptive engineering based on wall height, thickness, and soil strength, and always meet your local code minimums—you can over-build, but never under-build.

BuildBlock ICFs are an approved method written into the International Residential Code (IRC) and International Building Code (IBC). If your plan exceeds those specifications or the BuildBlock Engineering Manual, consult a local engineer; local codes always dictate final requirements. Remember that ICFs create an insulated solid mass wall, not a cavity wall, so mass-wall insulation requirements differ because of their superior performance.

Lay out footings and stem walls using ICF-friendly dimensions where possible, keeping exterior finishes and floor heights in mind, and level footings to within ¼ inch or less—shimming and trimming after the first two courses. Blocks settle slightly once filled, so leveling early prevents headaches later. Vertical rebar extends from the footing or stem wall up into the wall and overlaps to create continuous reinforcement; make sure dowels exceed code for wind load and backfill height. Rebar must sit at least three inches from any soil exposure, ¾ inch from the inside face of the foam, and 1½ inches from other faces such as bucking, to protect against moisture and provide proper concrete coverage.

Square the project before staging materials by verifying that diagonal dimensions are equal, then snap chalk lines on the footing marking the outside edge of the block—the outside face of the block is the outside face of the structure. A level, code-compliant, properly reinforced foundation is the base your entire project rests on, and care here prevents costly setbacks later.