Frost Protection Shallow Foundations (FPSF)
Author: admin
• Thursday, November 12th, 2009

View the ToolBase TechSpecs- Frost-Protected Shallow Foundations PDF file for an overview of this technology.

Frost-Protected Shallow Foundations (FPSF) provides protection against frost damage without the need for excavating below the frost line. An FPSF has insulation placed strategically around the outside of a foundation to direct heat loss from the building toward the foundation, and also to use the earth’s natural geothermal energy.

Traditionally, foundations are protected from frost-heaving damage by placing the footing below the frost line. Because FPSF are protected from freezing by thermal insulation, bottoms of footings can be just twelve to sixteen inches below grade. This reduces excavation costs, making this an economical alternative for protecting foundations against frost damage.

Insulated footings had been used as early as the 1930s by Frank Lloyd Wright in the Chicago area. There are now over one million homes in Norway, Sweden, and Finland with insulated shallow footings, recognized by their building codes as standard practice. It is estimated that there are over 5,000 buildings in the United States that have successfully used frost protected shallow foundations.

Frost-protected shallow foundations are similar to conventional foundations except for insulation placement and footing depth. Bottoms of FPSF footings are placed about 12 to 16 inches below grade. FPSF have vertical insulation placed at the outside edge of the foundation extending from above grade to the bottom of the footing. When required in colder climates, “Wing” insulation extends outward horizontally from the footing. The colder the climate, the further the wing insulation is extended. Wing insulation is unnecessary in moderate climates.

The insulation used in FPSF is commonly rigid expanded or extruded polystyrene foam suitable for below grade application, and it must be in compliance with ASTM C 578 Standard. FPSF can be used for both heated and unheated portions of a building.

 

Frost-protected shallow foundations (FPSF) allow bottoms of footings to be shallower than the normal code-required frost depth. This reduces the amount of excavation and concrete or masonry required, which reduces labor and material costs. Heating energy costs are also reduced because of increased perimeter foundation insulation.
Insulation around the perimeter of the foundation reduces the amount of heat loss from the warm interior to the cold exterior in the winter, which would normally pass through the slab or floor, and out through the foundation. Heating energy costs are thus reduced.
Frost-protected shallow foundations rely on building and geothermal heat to keep the earth around the foundation warm enough to preclude frost formation that might heave the structure. The foundation is wrapped with polystyrene foam that provides a thermal barrier and channels the escaping heat to warm the earth beneath the foundation. The method allows footing or foundation depth to be reduced from 48″ to 16″ in colder climates; representing a 2/3 savings in the amount of concrete needed, and with less excavation, disturbing less of the surrounding earth.
 
 

 

Frost protected shallow foundations are simpler to install than traditional foundations. Because they are shallower than conventional footings/foundations in a given region and rely on polystyrene foam for insulation, they can be installed with simpler equipment, like a trenching machine instead of a backhoe. The rigid polystyrene foam is a natural as a leave-in-place form, so once the style is mastered, crews find FPSFs easier and faster to install. Detailing the outside edge of the foam with a durable, attractive finish is the biggest challenge to a FPSF. 

 

Cost is highly dependent on building size and climate. Savings of $635-4750 have been reported.

 

Not Applicable