Climatic Data for Frost Protected Shallow Foundations (FPSF) is a product available from the National Climatic Data Center (NCDC). A frost protected shallow foundation (FPSF) is a practical alternative to deeper, more-costly foundations in cold regions with seasonal ground freezing and the potential for frost heave. An FPSF incorporates strategically placed insulation to raise the frost depth ... around a building, thereby allowing foundation depths as shallow as 16 inches, even in the most severe climates. The most extensive use has been in the Nordic countries, where over one million FPSF homes have been constructed successfully over the last 40 years. The FPSF is considered standard practice for residential buildings in Scandinavia. The objective of this web page is to provide US builders, designers, code officials, and others with the air freezing index (AFI) data necessary to employ FPSF technology. The AFI is a measure of the combined magnitude and duration of air temperatures above and below freezing during any given winter. The AFI, the thermal properties of the soil, and the surface soil cover are the major parameters used to determine the ground freezing potential of a given climate. The amount of insulation required to protect a foundation using FPSF technology has been found to be a function of the AFI. Cost savings to the buyers of new homes using FPSF have been estimated to range from 1% to 4% over the cost of conventional slab-on-grade construction or an annual savings of 00 million nationally. Additional long- term savings are expected from increased energy efficiency. Additional information on AFI is given in the documentation. Additional information on FPSF is also available from the National Association of Home Builders that describes this technology in greater depth.