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Joel
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93 Posts
Discussion Starter #1
I am getting ready to install a new basketball post. I need to dig a hole at least 3 1/2 feet deep and about 18" in diameter for the post's footing. The instruction manual indicates that using one of those giant tubes (sonotube) is optional. My question is this, should I just dig the hole and put the concrete and footing directly into the ground or should I use one of those cardboard tubes, pour the concrete in the tube and then put the footing in? I can't figure out what the difference(s) would be. Any thoughts would be appreciated.
 

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Concrete & Masonry
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3,841 Posts
Do to the heavy soils & frost in our area, I would def. reccomend a "sonotube" or an equivalent, like a 4x8 sheet of 1/8" masonite/hardboard. You will probably have to get it wet first (easy right now!) but you'll have an adjustable tube. The idea behind the tubes is to simply leave a smooth, non-tapered surface so that frost cannot lift/grab onto any part of the column. Have fun digging! :thumbup:
 

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Joel
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93 Posts
Discussion Starter #3
So what you are saying is that the tube prevents the soil from interacting directly with the concrete thus avoiding the possibility that frozen soil may potentially cause "frost heave?"
 

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Concrete & Masonry
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3,841 Posts
Yes, that's what i'm trying to say. Unless you can carve the hole near perfectly in the soil, you are better off using a tube or something smooth as a break between the two. What I'm not saying is that the concrete & clay will stick together. Hope that makes sense.
 

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Civil Engineer
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5,832 Posts
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.
 

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Concrete & Masonry
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3,841 Posts
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.
 

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Joel
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93 Posts
Discussion Starter #7
The instructions for this particular post (Goalsetter MVP) don't even mention using a tube. It's just something I was thinking of. The actual footing post itself is 42" long and is a 6" square.
 

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64 Posts
I agree that a form should be used when you place the concrete for the footing of your goal.

Smooth, formed foundation elements have much less surface area interacting with soil. Formed elements also have less chance of developing voids when the concrete is placed, and we all know that voids can allow moisture/frost intrusion. Having a jagged or rough faced foundation element in a an area with a deep frost line can result in up lift from expansive soils and increased chances of frost issues. It is my opinion that you need both a smooth, formed surface and to be below frost line in areas with deep frost.

In this case you have a very nice basketball goal and the added cost for the formed footing is next to nothing, so form the footing.
 
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