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 freshwater in the world is groundwater. A unit ...

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

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 conducti ...

properties of the soil and adjacent materials, and on nearby heat sources. For example, snow cover and

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...

insulate the ground and homes can heat the ground (see also ''

heat island An urban heat island (UHI) is an urban or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent ...

''). The line varies by latitude, it is deeper closer to the poles. Per Federal Highway Administration Publication Number FHWA-HRT-08-057, 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 ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...

and

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and othe ...

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

permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...

, and the term "

thaw depth In soil science, the thaw depth or thaw line is the instantaneous level down to which the soil has warmed to zero degrees celsius. The active layer thickness is the maximum thaw depth over a period of two years. The layer of soil over the thaw dept ...

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

elevation The elevation of a geographic 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 surface (see Geodetic datum § ...

below which

frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a g ...

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

Building codes

Building code A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permissi ...

s sometimes take frost depth into account because of

frost heaving Frost heaving (or a frost heave) is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated in ...

which can damage buildings by moving their foundations. Foundations are normally built below the frost depth for this reason. Water and sewage pipes are normally buried below the frost line to prevent them from freezing. Alternatively, pipes may be insulated or actively 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 which relate 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. Of the List of states and territories of the United States, fifty U.S. states, it is the List of U.S. states and territories by area, 34th-l ...

(2018) ***

Columbus, Ohio Columbus () is the state capital and the most populous city in the U.S. state of Ohio. With a 2020 census population of 905,748, it is the 14th-most populous city in the U.S., the second-most populous city in the Midwest, after Chicago, an ...

: 32 inches (0.8 m) **

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over t ...

(2007): *** Northern counties: *** Southern counties: * Canada: Can use table of estimates based on freezing index degree days. **

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

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

Ottawa Ottawa (, ; Canadian French: ) is the capital city of Canada. It is located at the confluence of the Ottawa River and the Rideau River in the southern portion of the province of Ontario. Ottawa borders Gatineau, Quebec, and forms the c ...

: ***

Windsor Windsor may refer to: Places Australia * Windsor, New South Wales ** Municipality of Windsor, a former local government area * Windsor, Queensland, a suburb of Brisbane, Queensland **Shire of Windsor, a former local government authority around Wi ...

References

{{DEFAULTSORT:Frost Line Glaciology Ground freezing Soil mechanics