Footing depth and height question

How deep do your concrete footings half to be in relation to how tall your sonotube is?

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Aug 26, 2011
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starstarstarstar 		Rule of Thumb
by: Editor - Rich Bergman

The real issue is not height of sonotube to the depth of the footing but the depth of the footing in relation to the width of the sonotube.

Force from a pier is directed downward and at the bottom of the pier the force is then dissipated straight downwards through the footing as well as at a 45 degree angle downwards and outwards from the outside walls of the sontube.

So, the rule of thumb is: Make sure the footing does not extend outwards from the pier or sonotube more than the depth of the footing.

Otherwise, the angled downward force can break off the part of the footing that extends beyond this 45 degree force line.

So if the footing is 8" deep, it should not extend more than 8" beyond the outside wall of the pier.

Tough to explain in words but simple with diagrams.

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