I was wondering what the vertical load capacity of a 4"×4"×.25" 6063 square aluminum tube is at 8' tall.

I have a small front porch with only the roof above it. There are 3 wood posts holding it up now, one on each corner and one in the middle. The porch is approximately 16'× 7'. Would it be feasible to use 3×3×.25 as well? Just looking to see what the likelihood of them failing is.

I live in the St. Louis area so large snow falls and high winds are possible but not a constant threat.

  • Existing posts are 6×6 wood that are rotting away at the bottom
  • I would like to keep the same post layout as that's where the bollards are
  • Aluminum is easily accessible for me and and I won't ever have to worry about rot or splitting.
  • Aluminum will be easier to work with especially by myself and I can always wrap it with wood down the road if I choose and that can be replaced when needed without dealing with braces and structural issues.
  • 2
    Steel will probably cost less and hold more in the same sizes. Galvanized and/or with good paint it won't rust, if that's your reason for thinking Aluminum, or pretty normal to wrap it with wood (or plastic trim boards if rot's your problem) "for show" so cosmetic rusting isn't an issue. You don't actually say what your issue with the present wood posts is, for that matter - presumably they are holding the roof up, and have been doing so?
    – Ecnerwal
    Dec 7, 2022 at 14:06
  • 1
    Why go to metal posts (especially if they are square)? Dec 7, 2022 at 16:12
  • Also, have you considered 4 posts instead of 3? That changes what you can use. Dec 7, 2022 at 16:14

1 Answer 1


I have no data for 3x3 but here is some guidance for others.

Here is the load bearing for round Aluminum columns.

It starts at 16,000 lbs.


And for your square


For more details on square look up here square Found at Al load

In summary the answer is yes you can use 4 x 4 to support your roof and snow on it

  • 1
    The OP is asking about square tubing, yet you post the data for round tubing and provide a link to the square tubing table. Seems... backwards...
    – FreeMan
    Dec 7, 2022 at 13:37
  • Doubly useless, it starts two sizes above the OPs size selections, too.
    – Ecnerwal
    Dec 7, 2022 at 15:12
  • So long as OP is considering fluted posts, this is better. Unfortunately, the chart starts at 4x4 AL, so it doesn't answer the 3x3 part of the question, but that's borderline a 2nd question...
    – FreeMan
    Dec 8, 2022 at 13:27

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