What are Shallow Frost-Protected Foundations?

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Top-down schematic view of shallow frost-protected foundationsShallow, frost-protected foundations are a modern innovation that uses both vertical and horizontal insulation to keep a building's foundations warm. As a result, structures can stand on much shallower foundations than would normally be possible, especially in colder climates.

The basic idea is to lay insulation in the area surrounding the foundation so that more building heat is retained. This protects the foundations from frost. The diagram at the top of this article shows how the insulation is laid out around the edges of the site, with a foot or two laid horizontally along the wall lines and two to six feet around the corners, where heat loss is the greatest. The exact amount of insulation depends on the climate.

Shallow, frost-protected foundations were used by Frank Lloyd Wright in the 1930s and (like many energy-saving innovations) gained more popularity in Europe than in the US. Scandinavian countries in particular found the frost protection extremely useful – so much so that modern buildings in those regions now use the design as standard.

The innovation is ideally suited to slab-on-grade foundations. It can be used (with modifications) on almost any kind of foundation, such as stem wall, floating slab or unvented crawl space designs. It can even be applied to commercial buildings. However, it cannot be used in areas where there is permafrost or permanently frozen ground (e.g. Siberia, Alaska, Northern Canada and so on). In simple terms, if your region's average annual temperature is below freezing, forget it.