Frost Protected Shallow Foundation

What are they?

The Frost-Protected Shallow Foundation (FPSF) technique is an internationally recognized alternative method of protecting slab-on-grade foundations of heated buildings against frost heave. The foundations can be monolithic slabs with thickened edges or floating slabs with grade beams made of concrete, concrete block, or treated wood.

How do they work?

FPSFs use rigid polystyrene slab-edge insulation to reduce slab-edge heat loss and hold heat from the house in the ground under the footings. This keeps the ground temperature under the footings above freezing.

In colder climates, horizontal ground insulation is also placed around the foundation, and extra insulation is placed at the corners of the foundation where heat loss is higher than along the walls.

The insulation raises the frost line around the foundation. It prevents frost heave anywhere in the U.S.-even where footings are placed only 12 inches below grade, plus four inches of non-frost-susceptible gravel.

What are the benefits of FPSFs?

FPSFs increase home energy efficiency because the slab edge is insulated. They provide frost protection equal to or better than that provided by deep foundations because FPSFs are based on stringent ground conditions using the coldest winter temperatures likely to occur in each area of the country in 100 years. In addition, raising the frost line reduces construction costs by decreasing excavation depths and disturbs less soil on the site.

Where are they approved?

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.

Click here for photos of Bear Creek Dome FPSF installation.

Click here to download FPSF design manual.

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