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We moved into a house that backs up to some trees and a small creek. There aren't any good trees for a tree house back there, but I would like to build a raised fort for the kids instead. It will be about 12'x8' and 7' off the ground.

I would prefer to use stand-offs so the support posts aren't buried. The soil is pretty moist and I'm afraid the support posts would rot off. However, we get really high winds at times and this will be free-standing. I know burying the posts would provide a lot more stability.

Will stand-offs work OK and be able to withstand high winds or are they only meant to be used on structures that are attached to something?

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    You already suspect the answer - no, your free standing, top heavy structure will NOT be safe in high winds. It'll be top-heavy and the right wind will blow it over. Anchor it properly. – The Evil Greebo Jul 14 '14 at 10:28
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X-brace the structure (under the raised deck of the "fort" part) so that the posts work together to BE a structure. Run opposing diagonal lumber from the bottom of one post to the top of the one next to it, and vice versa. At that point your posts should not be bending at the attachment point, so they should stay put just fine.

  • That will keep the legs nice and stiff. That won't prevent what will be a FREE STANDING top heavy structure from being blown over in the wind. – The Evil Greebo Jul 14 '14 at 10:27
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In such situations, implanted (vertical) pipe can be used.

For 4x4 posts, I'd choose 6 inch pipe.

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Cut the pipe and dig holes as appropriate, perhaps so that 2–3 feet are underground and only 4-6 inches are above ground. If the ground is soft or wet below that, place pier foundations first.

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Temporarily secure the pipe segments in place with stakes, scrap lumber, or what-have-you. Partially fill the pipes with cement to the support level, maybe about ground surface level. Let cure. Fill holes, remove temporary support, insert posts and build the frame. Then finish filling the pipes with cement to hold them down in wind and prevent water accumulation within the pipe.

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