0

I was thinking of surrounding my firepit with a hexagonal pergola, each side probably about 14' long, arranged like the the below image but wondered about the base. Each of the 6x6 posts would be connected by boards at the top (maybe 1x6 or 2x6) and I thought the shape itself would lend to pretty good stability. I was trying to think what would be best for the base though. The ground here is heavy clay so I was concerned about putting 6x6x12 posts 4' in the ground (Western NY) due to the poor drainage.

My other thought was putting in concrete footers and using 6x6x8 posts. Would that be a better option? I have not worked with concrete footers before though there seem to be vids out there using form tubes and it seems a simple process. Not sure how well the fasteners hold and would want to avoid any sway in the structure (the top connectors would just be post to adjacent post, no cross beams in the plan) Between posts I may eventually put in swings but at most probably hammocks. Any advice would be great!

enter image description here

6
  • 1
    Your question is a bit vague. Are the footings to be up to grade? If so, your pergola needs to be entirely self-supporting. No connector short of custom heavy steel is rigid enough to withstand wind and human loads. Also, the hexagon is not inherently stable--each corner is effectively a hinge. You need diagonal bracing if your posts aren't buried deeply--either on the vertical or horizontal plane.
    – isherwood
    Commented May 12, 2023 at 13:06
  • Please revise to be more clear about what you're asking. There are quite a few pergola questions on this site already (some in the Related list at right), so have as look at those, too. See How to Ask and take the tour for tips.
    – isherwood
    Commented May 12, 2023 at 13:08
  • 1
    Correction: Since your pergola isn't attached to another structure you need diagonal bracing on both axes, or at least all vertical planes.
    – isherwood
    Commented May 12, 2023 at 13:13
  • I believe Stone is the traditional approach to making a henge like this, and has the advantage of not rotting below-ground. Do set the sarsen stones carefully so none of your lintels fall down over the course of 5000 years or so.
    – Ecnerwal
    Commented May 12, 2023 at 16:56
  • That's a very light, elegant and unstable looking design. Just imagine 2 adults (even small ones) in each swing, all swinging in unison. The rocking forces on that thing will have it disassembled rather quickly!
    – FreeMan
    Commented May 12, 2023 at 18:49

2 Answers 2

1

Practically speaking, buy long-enough "ground contact rated" pressure treated posts, and save the documentation so you can collect on the "lifetime warranty" if it's not up to snuff.

1

I would approach this very carefully. Swings and hammocks are not a lot of weight, but the swinging can definitely cause problems if the structure is not properly secured to the ground.

I would consider either:

  • Concrete in the ground (e.g., Sonotube, but can be any brand or could be poured into a wooden form - doesn't have to be round) with the posts on top, attached with metal brackets (e.g., Simpson Strong-Tie, but can be any brand). A structure built this way can be very strong, but it requires the rest the pergola to be built appropriately to match - e.g., diagonal bracing. With posts in metal brackets, if there is too much load - because the rest of the design is not stable in wind or with human loads (swings, hammocks) - then the posts will either snap off of the brackets or bend the brackets, which would not be good.

or

  • Dig a hole. Stick in a post. Pour fast-setting concrete around it. The advantage of this is that it is fast and easy. But I see this commonly done for fence posts, which (a) are not as tall as pergola posts and (b) don't generally need to be as carefully lined up.

But I wouldn't just stick the posts in the ground. That might work OK for a fence but I wouldn't trust that for a pergola with swings or hammocks.

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.