In cold climates, frost is a phenomenon that can occur during three seasons of the year, and it can be a serious problem for building foundations. One way to protect a foundation from the damaging effects of frost heave is to build a deep foundation wall that rests on a footer well below the frost line. A frost wall, however, can keep even a shallow foundation from being damaged by frost.
Frost heave happens as the outside temperature falls and the water in the soil begins to freeze. Ice in the soil accumulates in a structure called an ice lens, and additional groundwater is drawn to the developing ice lens through capillary action. The ice lens grows, and because water expands as it freezes, the quickly expanding ice pushes with great force on the surrounding soil. Nearby underground structures such as building foundations can be shoved upward and damaged by the action of the ice. Damage to foundations can also occur when ice in the soil adheres to the foundation wall itself, allowing the frost to exert an even stronger upward force on the wall.
Frost-Protected Shallow Wall
The purpose of a frost-protected shallow wall is to prevent the soil surrounding a building's foundation from freezing by using the heat that radiates from the building to warm the soil. A layer of rigid foam insulation is applied vertically to the outside of the foundation wall, and another layer of rigid insulation is placed horizontally under the soil at the base of the foundation wall. These layers of insulation direct the warmth from the heated interior of the building downward into the soil and keep it there so that the soil does not freeze.
Unheated Frost-Protected Wall
A traditional frost-protected shallow wall relies on the warmth radiated by a heated building, but it will not protect an unheated building. An alternative design will, however, help protect even an unheated building. In this design, a horizontal layer of insulation is laid under the building's entire foundation and extends outward from the foundation, but there is no vertical insulation. The layer of insulation rests on a layer of gravel. This method takes advantage of the temperature of deeper layers of earth, which remain between 40 and 50 degrees year-round; the warmth of the soil is stored and radiated upward, preventing the upper layers of soil from freezing.
Interior Frost Wall
An interior frost wall is an insulated wall that is framed against a concrete basement wall to prevent frost from forming on the inside of the basement. The wall is framed using 2x4 studs between a top and bottom plate, with the framing installed 3/4 inch from the concrete wall to allow for airflow behind it. Insulation is installed between the studs, and a vapor barrier is stapled over the insulation. The wall is finished with drywall.