Weather Break

From the Creighton University Department of Atmospheric Sciences

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The Frost Line

January 14th, 2009 · 3 Comments

Click here to listen to episode 448 of Weather Break.

The depth to which water in soil will freeze in the winter is known as the Frost Line. The depth of the Frost Line is important because it influences the construction of buildings and roads; since water expands as it freezes, infrastructure above the Frost Line can be prone to burst pipes, cracked foundations, and similar problems. However, predicting the exact depth to which the soil will freeze is actually incredibly difficult, depending on detailed information about the weather, the soil moisture and temperature, the thermal conductivity of the soil, and other factors. On today’s episode of Weather Break, Dr. Jon Schrage takes a look at some of the reasons why it is so important to know the depth of the Frost Line in your neck of the woods.


I found online this map of estimated average depths of the Frost Line across the continental United States.  It looks pretty reasonable to me, but I can’t help but notice that it claims to be from the “Weather Bureau”, which changed its name to the “National Weather Service” decades ago, so maybe this information is obsolete.

Tags: Basic Meteorology · Climate · Winter Weather

3 responses so far ↓

  • 1 Wayne // Mar 17, 2009 at 6:54 am

    I’m looking for a frost line chart of United States that would show depth to indicate at what depth you should have footings designed for buildings.

  • 2 schragej // Mar 17, 2009 at 8:14 am

    Wayne: Yeah, that’s the kind of stuff that we hoped to find online when we started working on this episode, but we never came across anything like that. We suspected that there was probably a “legal” reason why nobody posts stuff like that–for example, maybe you could get sued if the information was wrong and a foundation failed. I don’t know, but it was conspicuous that stuff like that was hard to find online.

  • 3 June // Jan 21, 2010 at 10:00 pm

    I am after similar information. However, after reading a substantial part of the following reference, I gave up the broad approach. See: \\\ Location of points of ground stability — necessary for markers and for building footings — is not only difficult but cannot be generalized by area. Frost upheaval alone varies with type of soil, relationship to water table, etc., etc. A single city lot can have extremes. Therefore, for my particular problem, I have decided to try to squeeze out info on how deep the water lines are buried on my lot or, at least, in the immediate neighborhood. That should give some clues. I think. \\\If you go to the NOAA ref above, note that the home page suggests clicking on the link to the PDF file for more accurate info.

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