A frost protected shallow foundation (FPSF) is a practical alternative to a deeper, more-costly foundation in cold regions with seasonal ground freezing and the potential for frost heave. The International Residential Code® (IRC) includes prescriptive methods for constructing frost protected shallow foundations in heated buildings. By the IRC reference to ASCE 32-01 (American Society of Civil Engineers, Design and Construction of Frost-Protected Shallow Foundations, 2001), FPSFs in semi-heated and unheated buildings that meet the requirements of the IRC may also be designed and constructed.
The objective of the document to which this summary links was written to assist U.S. home builders, remodelers and trade contractors in the design, construction, and code approval of frost protected shallow foundations.
How a Frost Protected Shallow Foundation Works
A frost protected shallow foundation allows builders to construct a structurally sound foundation that is more resource efficient and less costly than a conventional foundation. The FPSF technology recognizes the thermal interaction of building foundations with the ground. Heat input to the ground from a conditioned building effectively raises the frost depth at the perimeter of the foundation.
The effect of heat from the building is magnified when insulation is strategically placed around the foundation. Frost protection of an insulated foundation also works for an unheated building by conserving ground geothermal heat beneath the building. Unheated areas of homes, such as garages, may be constructed in this manner.
Where Frost Protected Shallow Foundations are Suitable
Frost protected shallow foundations are most suitable for slab-on-grade homes on sites with moderate to low sloping grades. Slab-on-grade FPSFs can be installed with one placement of concrete, eliminating multiple inspections and speeding construction time. The method may also be used effectively with walkout basements by insulating the foundation on the downhill side of the house. Frost protected shallow foundations are also useful for remodeling projects because their installation minimizes site disturbance. In addition to residential, commercial, and agricultural buildings, the technology has been applied to highways, dams, underground utilities, railroads, and earth embankments.
The document to which this summary links presents an FPSF design procedure for slab-on-grade, stem wall foundations, and unventilated crawlspace foundations, and includes design examples, and specific construction methods and details. Additionally, a simplified design method adopted by the IRC is presented.