FROST-PROTECTED SHALLOW FOUNDATIONS, or FPSFs, provide protection against frost damage without the need for excavating below the frost line. FPSFs feature insulation placed strategically around the outside of the foundation to direct heat loss from the building toward the foundation and to use the earth's natural geothermal energy. Because of the reduction in excavation costs, FPSFs are an economical alternative for securing foundations.
In the 1930s, Frank Lloyd Wright used insulated footings in the Chicago area. There are now over 5,000 buildings in the United States, and over 1 million homes in Norway, Sweden, and Finland with insulated shallow footings.
An FPSF can be incorporated into slab-on-ground construction, but it can also be used for stem wall, floating slab, and unvented crawl space foundations. The NAHB Research Center originally published “Design Guide for Frost Protected Shallow Foundations” to help determine proper foundation design and insulation details.
An updated version of the guide is now available. This new and improved version includes design procedures, detailing applications and limitations, insulation selections and design processes, and recommended construction methods. For example, the FPSF technique can be applied to additions to homes with existing conventional foundations, and even walk-out basements. The guide fully explains each of these options. It also contains descriptions of several typical design approaches, such as brick veneer and independent slab wall.
The new version of the guide features updated graphics and detailed drawings of the prescribed methods of using FPSFs in constructing slab-on-grade foundations in cold climates with seasonal ground freezing. Additionally, since the International Residential Code now includes prescriptive methods for building FPSFs, the guide focuses on FPSFs in heated buildings and attached unheated buildings such as garages. Tables now include a simplified comparison of the FPSF design requirement and the energy-code design requirement.
To obtain a copy of the latest edition of “Design Guide for Frost Protected Shallow Foundations,” visit www.toolbase.org/fpsf.