Footing For Basketball Post???

I have never heard the claim before that a sonotube reduces the chance of frost heave due to its smooth surface. The normal explanation for frost heave is water BELOW the foundation which freezes, and expands, lifting up the foundation. That is why foundations are by code required to be dug below the frost line.

Foundations which are dug below frost line do not heave, yet the soil moisture above the frost line is subject to freezing, so the theory that frozen soil in contact with a concrete footing causes frost heave does not seem to hold water (pardon the pun).

The sonotube manufactures simply claim (correctly) that a sonotube provides a convenient, low cost form for placing concrete, and can be easily stripped later if the concrete is exposed. If you dig a hole in the ground and do not use a sonotube, you may use more concrete than required, since the walls of the hole are almost certainly not going to be perfectly vertical.

When I put in my basketball hoop, I did not use a sonotube, I simply dug a hole and placed concrete. The manufacturer specified the minimum weight of concrete required. For my shed, I did use sonotubes.

A basketball hoop is not a frost critical application, unlike a foundation. If you do use a sonotube, and want to avoid frost, you still need to get the bottom of the tube below the frost line, don't count on that slippery cardboard to stop frost heave from below.

Daniel, no offense, but you've obviusly never seen frost "pick" at the side of the structure & cause damage. Maybe your area doesn't frequently see over 3 feet of frost in winter, or you dont have heavy, expansive clays as are common in our area. I glanced quickly for something in our foundation codes, but couldn't find it. Most inpectors that I deal with will not let us count the depth of the footing in total frost protection depth UNLESS it is formed on both sides. Example: We have 48" minimum frost protection in our code. Assuming soil against attatched garage wall is to remain 6-8" below wood bottom plate, the foundation wall would have to be 4'8" tall, or 7 courses high if the footing isn't formed. Think of it this way otherwise: You have a trapezoid with the top & bottom parrellel, wider on top than the bottom (as every excavated hole is, whether hand or machine dug) & the bottom is below frost level. You cant see how this would be succeptable to heaving do to frost? Remember, expansive soils expand in outward as well as upward. Either way, I'd stick the money in a tube or sheet for 2 reasons: the directions called for it & the money spent for a tube/sheet is less than he'll spend on the extra concrete.