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Aptos, CA, United States

What service or documentation resource can I use to determine what the frost-line is for my area? I'd be inclined to ask the county building/planning office but I suspect that they'll want to charge for answering a seemingly simple (and hopefully well documented) question.

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up vote 2 down vote accepted

In general you can use these guidelines.

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These are very good guidelines that are widely recognized. However if getting inspected I would just ask your building department for their code requirements.

NOTE*** This is how deep your footings would be in undisturbed soil. So for example if there was a regrading of the land - as often the case in new builds - you would have to go this deep past the disturbed soil or consult an engineer that would sign off on something else. So if they regraded your land to 3 feet and you lived in Arkansas you would need to go to 54 inches or gets clearance from an engineer to put the footings shallower.

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What is the source/age of this data? It contradicts data I have seen elsewhere by a large margin in some areas. In SW Michigan, for example, this says 3 feet, whereas other sources give 4+ feet. – Necreaux Sep 20 '15 at 18:48
@Necreaux - This is the building code minimum. This is still current. A local county/municipality can obviously ask for more. – DMoore Sep 20 '15 at 20:53

The 2010 California Residential Code has a beautiful table (TABLE R301.2(1)) to list the frost lines; however, that is empty.

The Santa Cruz County Municipal Code states "Frost line depth = 12 inches below undisturbed soil". Search for "frost line".

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This map showsFrost Line Depth the frost line depth for each state.

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Hello, and welcome to Stack Exchange. This is very cool; what is the source? (Any clue why the frost is so much shallower on the Lower Peninsula of Michigan?) – Daniel Griscom Jul 14 at 0:18

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