Frost Protected Shallow Foundations

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 (see comparison graphic). 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. Scandinavia considers FPSF a standard practice for residential buildings.

Standard Foundation compared to Frost Protected Shallow Foundation

Cautionary Note When Using Air-Freezing Index Values: Topographic variability, proximity to bodies of water, and urban heat effects should be considered when using these data. For those locations or if the planned construction site is not located nearby a station that has AFI data, using a combination of the AFI map and the most representative city(s) AFI value(s) is advisable.

Maps

These map analyses use data from 3,110 cities to interpolate the 100-year return period of the AFI for the continental United States, Alaska, Hawaii, and Puerto Rico. The data tables contain the actual 100-year return period AFI values for these cities.

• Mean Annual Air Temperature based on the 1961–1990 Normal Period
• Air-Freezing Index, Estimate of the 100-year Return Period, United States
• Air-Freezing Index, Estimate of the 100-year Return Period, Alaska
• Air-Freezing Index, a Simplified Analysis of the 100-year Return Period 

Data Tables

The data table publication contains a list of cities with the specific 100-year return period value located in the far right column. Other columns in the table contain lesser return periods and are listed for comparison purposes or other applications. Use only the 100-year return period in this publication for FPSF.

• Air-Freezing Index Return Periods and Associated Probabilities
• Air-Freezing Index Return Periods and Associated Probabilities Spreadsheet
• Air-Freezing Index Seasonal Data
• Air-Freezing Index Seasonal Data Spreadsheet

Documentation

The technical publication below contains the methodology used to create the 100-year return period of the AFI. Pages 8–11 provide an overview and sections on AFI data applications and a description of the AFI return period estimates. Pages 7–8 contain references that supported this work.

•  Air-Freezing Index Statistics for the United States (DSI9712D)

The National Association of Home Builders provides additional information on FPSF that describes this technology in greater depths on their website. In 2001, the American Society of Civil Engineers and the International Code Council approved ASCE 32-01 for reference in the 2002 addendums and 2003 editions of the International Building Code and International Residential Code. The standards committee consisted of individuals from many backgrounds including consulting engineering, research, testing, manufacturing, construction, education, government, and private practice.