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appropriate footing frost depth
what is the correct point on a footing's depth to be considered below frost depth?
top of footing or bottom of footing?
where would i find the code that indicates which of the two is correct?
thank you!
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for ibc jurisdictions:
the frost depth is generally not found in building codes, but the ibc -residentialcode as least states that local jurisdictions shall determine the depth
bottom of footing is the depth.
tbell47,
having the bottom of footing below(at least)the frost depth is typical practice if the uplift is a concern (of structural/piping/building/whoever), and if the footing is exposed to frost.
uplift from frost is a relatively tricky item, it is from frost heave on the footing bottom surface and adfreeze on side faces above the frost line of the foundation. putting footing (bottom face) below frost depth eliminates the heave but may not be good enough. sometimes the adfreeze stress plays a big role. usually, there should be a calculation to have the downward force (by dl, selfwt of fdn and friction on the foundation below the frost depth) to balance the uplifting force (by frost heave and adfreese stress).
i don't know if any code tells where to found the footing. local geotechnical companies (if you don't have a soil's report for a project)usually give very good advice.
hope this helps
connecticut and massachussetts codes list frost depth requirements for our states.
read

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