Expert: Dan Griffin - 7/13/2008

Question
QUESTION: The pro hoops company indicates it is imperative that the concrete pier be at least a 2' x 2' square that is 4' deep.  Someone suggested I use a 24 inch sonotube.  I am in Wisconsin and plan to go 5' deep.  Will the 24" cylinder be enough concrete?  Do you have other suggestions?  The pole is 6" x6" x 3/16" thick.  There is a 4' extension arm for the backboard, and the backboard is 72" x 42" x 1/2" tempered glass.  I don't have the exact weight, but the pole components are extremely heavy for 2 men to move and the backboard is also a good lift for 2 guys.

Thank you,  Doug Burge

ANSWER: I had a friend contract to install one of these for a local doctor for his kids.  We both were surprised by the requirements.  We assume they want the weight to conteract tip over.  His soil was fairly easy digging and so they stayed on blueprint digging with shovels and post hole diggers.  They weren't worried about a perfect square.

2x2x4=16 cubic feet of concrete @ 155 lbs per cf = 2450 lbs
24" sonotube pi r^2 x 5= 15.7 cf @ 155 = 2433

Close enough, but why the sonotube?  The square shape helps prevent the goal from turning, the sonotube adds expense.  How were you planning the excavation?  As I recall, the tube has some cross pipes to lock the tube in the concrete.

---------- FOLLOW-UP ----------

QUESTION: I ran into a guy this winter who works as a concrete laborer and told him about the dimensions for my basketball goal.  He said to use the sonotube because the freeze and thaw that we go through causes breaking where there are jagged edges from just pouring into a hole.  I wanted to ask about this because it seems like people have been pouring without forms for years.  My thinking is that these jagged pieces will just break off at the edges and not cause breaks through the entire pier.  Does this make sense?  

I dug the hole with a shovel, but it is at least 30" x30" at the top and slightly smaller at the bottom.  It is also a compromise between square and circular because I was planning to backfill around the sonotube.  The hoop comes with rebar pieces to push in after the pour. I am now thinking I should square off the top half as much as possible and just pour the concrete in the hole.  It will definitely be 30" x 30" for the top 3 feet.  Should I worry about building a square form for that portion?

Thanks for your expertise!

Answer
I disagree with your fella.  Remember that you want to hold the top of the concrete lower than finish grade so you don't have a big jagged lump to deal with around the goal post.  Square is not important, I just meant that some shape other than smooth and round would prevent the pole from turning in the hole or turning the hole.  Hurry up and get the thing poured so you can use it!