I want to hold up my water tower with sonotubes and concrete post anchors. Is 4 foot of 6" wide tube per post sufficient? (Posts are 6x6s).
Some areas have no frost, like coastal Vancouver island and only require the soil be suitable bearing. Other areas can be up to 6 feet. Other locations still you can build right on permafrost just a mere 6" below the topsoil.
Check with your local municipalities building department to get accurate information.
Frost depth varies. Toronto is 48" but Madoff may be more, call your local municipal building department and they can tell you. I would install larger sonotubes with flared bottom section for increased bearing capacity. Water is very heavy and the 6 " tube may be undersized.
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