The frost line—also known as frost depth or freezing depth—is most commonly the depth to which the

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

is expected to freeze. The frost depth depends on the climatic conditions of an area, the

heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...

properties of the soil and adjacent materials, and on nearby heat sources. For example, snow cover and asphalt insulate the ground and homes can heat the ground (see also '' heat island''). The line varies by latitude, it is deeper closer to the poles. The maximum frost depth observed in the contiguous United States ranges from 0 to . Below that depth, the temperature varies, but is always above . Alternatively, in

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

and

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

locations the freezing depth is so deep that it becomes year-round

permafrost Permafrost () is soil or underwater sediment which continuously remains below for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below ...

, and the term " thaw depth" is used instead. Finally, in tropical regions, frost line may refer to the vertical geographic

elevation The elevation of a geographic location (geography), ''location'' is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational equipotenti ...

below which frost does not occur. ''Frost front'' refers to the varying position of the frost line during seasonal periods of freezing and thawing.

Building codes

Building codes take frost depth into account because of frost heaving, which can damage buildings by moving their foundations. For this reason, foundations are generally built below the frost depth. Water and sewage pipes are typically buried below the frost line to prevent them from freezing. Alternatively, pipes may be insulated or heated using heat tape or similar products to allow for shallower depths. Due to additional cost, this method is typically only used where deeper trenching is not an option due to utility conflicts, shallow bedrock, or other conditions that make deeper excavation infeasible. There are many ways to predict frost depth, including factors related to air temperature, soil temperature, and soil properties.

Sample frost lines for various locations

* United States **

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

(2018) ***

Columbus, Ohio Columbus (, ) is the List of capitals in the United States, capital and List of cities in Ohio, most populous city of the U.S. state of Ohio. With a 2020 United States census, 2020 census population of 905,748, it is the List of United States ...

: 32 inches (0.8 m) **

Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...

(2007): *** Northern counties: *** Southern counties: ** Washington (2023) *** Edmonds, WA: 18 inches (0.46 m) *** Spokane, WA: 24 inches (0.61 m) * Canada: Can use table of estimates based on freezing index degree days. **

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

: Map of frost penetration depths for Southern Ontario. ***

Ottawa Ottawa is the capital city of Canada. It is located in the southern Ontario, southern portion of the province of Ontario, at the confluence of the Ottawa River and the Rideau River. Ottawa borders Gatineau, Gatineau, Quebec, and forms the cor ...

: *** Windsor:

References

{{DEFAULTSORT:Frost Line Glaciology Ground freezing Soil mechanics