The pole is overall 29’ 6” tall with a flange welded on the bottom. Flange: 13” x 13” x 3/4” thick with 4 slots for attaching. The flange is welded to the pole in two places, on the inside bottom and 3 1/2” up from the bottom to the pole on the outside. Where it’s welded the Dia. Is about 8 3/4” and tapers down to about 4 1/2” at 29’. Oh, and the slots in the flange are 2” x 1 1/2”. What do I need for a base to keep the wind from tipping it in the ground and inner support so the concrete doesn’t break.

  • 2
    That would in part depend on your local wind loading. In any case a fairly substantial base will be required, with a fair bit of reenforcing steel and suitable anchor bolts attached to the reinforcing steel.
    – Ecnerwal
    May 5 at 16:00
  • a lamp post may not be able to withstand the force that a large flag exerts in high wind
    – jsotola
    May 5 at 16:08
  • @jsotola A flag attached on one side should not add much wind load. A flag on a frame fixed in place would add a big wind load. May 5 at 16:26
  • ~30 feet is a big lever for tipping. Your anchor in the ground will depend on the type of dirt and frost level. I would not be surprise if you will need to go down close to six feet or more, plus needing a surface close to 2 feet x2 feet or more. Guy wires might reduce these sizes.
    – crip659
    May 5 at 16:35
  • I live in Lyons, Michigan. When I did research I think it said the highest wind gust ever recorded for this area was 64 mph, I’m not sure what our average wind speed is. The frost depth here is generally 42 inches.
    – Dave
    May 5 at 17:10

1 Answer 1


6' deep and 24" diameter base with rebar. You need minimum 3000 PSI concrete.

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  • Good use of local to the questioner public resources for a thorny question. +1
    – Ecnerwal
    May 5 at 21:04

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