Frost line

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Izabela Toma

August 22, 2024 21:56

Hi,

I understand the basic concept, but I am seeking clarification on whether a foundation should be placed below or above the frost line. I've encountered conflicting information from different sources, which has led to some confusion.

Thank you.

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  piyarudee August 23, 2024 13:28 (Edited August 23, 2024 13:29)

  From Chen's PA mock exam, it says the bottom of the foundation should be place at the frost line as a MINIMUM requirement (I can take a look at this when I get home to confirm). But generally, a foundation should be placed below the frost line. 

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  Galchenko12 August 24, 2024 00:43

  Hi, the exterior foundation needs to extend at least 12 inches BELOW the frost line to prevent the frost heave. 

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  Izabela Toma August 24, 2024 19:09

  Thank you for clarifications on this.

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  Rajan Karmacharya October 02, 2024 20:31

  Izabela, frost heave occurs when water in the ground freezes and expands, pushing the soil upward. To prevent this from impacting a building's foundation, the foundation must extend BELOW the frost line. The frost line is the depth at which the ground is expected to freeze during the winter. By extending the foundation at least 12 inches below this frost line, the foundation is placed in soil that remains stable and does not freeze, preventing the expansion and contraction of the soil from exerting pressure on the foundation. This design practice helps ensure the structural integrity of the building and prevents issues such as cracks in the foundation or uneven settlement due to frost-related soil movement.

  In practice, the specific depth of the frost line varies depending on geographic location, so local building codes typically provide the minimum depth for foundations to ensure they extend below the frost line in that area. For instance, in colder climates, the frost line might be deeper, requiring a more substantial foundation depth. I hope this helps understanding the concept better.

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