How to Build: Frost Walls and Stem Walls
Frost Walls or Stem Walls, transfers the weight of the building from grade to the footing. Place the foundation walls on a footing that is situated at or below the frost line for your region. This ensures stability.
This will prevent the soil that the walls are resting on from “heaving”, causing cracks and misalignment. Typically, ICF foundation walls are extensions of the 1st-floor walls and are laterally supported by the floor system. The concrete can be poured inside the foam of the floor system and “float”. It can also be poured so that the concrete of the floor and walls are joined. Pour the concrete either at the same time or with a cold joint and dowels.
The foundation is used anywhere there is a minimum depth for the footings, as required by local codes. It can also be used where structures require additional attachment to the ground for wind or other forces acting against them. In the US, common frost depths range from 12 inches in southern states (some with no requirements for frost) to 4 feet in more northern states. In fact, Canada and Alaska have even deeper frost lines.
Areas with volatile soils, meaning the soils expand and contract with temperature or moisture content, it may be necessary to place piers below the footings or foundations. If sited directly over rock, then a footing may be unnecessary and the foundation can be placed directly against the rock, and have rebar or other reinforcing steel installed by drilling and driving it directly into the substrate. Additionally, having an insulated foundation serves a number of purposes. It will help to keep the soils placed inside of the foundation wall from freezing, and eliminates any frost heave against the floor. It will also reduce the heat loss through the floor and into the soil as a heat sink, and help to prevent water and drain lines from freezing in the winter.
Additionally, basement walls also act as a foundation wall, by transferring the loads as before. A walkout basement, however, may have a foundation wall placed below the frost line at the walkout area, and for a certain distance back as the grade rises, to ensure the footings remain below the frost line. To match a stepped footing, foundations can also be stepped. Also, you may also see a footing at the basement level with a Sonotube or stacked ICF wall extending upwards to another footing situated at frost depth, and extending away from the basement, to carry the end of this foundation down to the lower level with undisturbed soils.