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| Posted By |  Subject :poles in the ground vs. concrete footings with anchor |
My neighbor built his 70x100 30 years ago and has replaced about half his treated poles that were set in concrete. Speaking with barn builders here in SE Michigan they say the concrete causes the poles to chemically break down and rot. And since treated wood shrinks, water gets trapped between the wood and the concrete pour. The quick solution is to put the poles on a pad in the hole and backfill with the spoils. A company called FBi Buildings (www.fbibuildings.com) offers a pre-fab concrete "pole base" with an integrated, large "u" shaped bracket attached to the top, similar to the description above about a metal bracket in wet concrete only these are ready-made to drop in the hole. It seems one could even build the walls on the ground and tip them up into the bracket/pole bases though they don't show that in their publications (they show a telescopic material handler dropping the walls into the brackets from above)
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| This doesn't support the argument for using concrete around poles but this was the alternative I used for satisfying local building codes: I had to dig a "ratwall", "frostwall" or "footer" 8" wide x 42" deep for an 18'x32' barn with anj integrated lean-to. I suspended the poles over the perimeter trench with 2x6's and diagonal bracing. The trench was dug out wider and deeper at the poles, then concrete was poured up to the rough grade effectively locking in the poles (until they shrink). Once the foundation concrete cured, I then installed the 2x10" treated base/grade boards which worked great as a form for pouring the floor. After the floor was poured a second row of grade boards were installed with a bead of sealant between the rows. The first row of grade boards were lower on two sides than final grade and were eventually backfilled against. It worked out quite well.
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Around here, Code says any wood contacting concrete has to be treated, so there would have to be at least a 2-by section under the post. I wrestled with bracket idea, but then decided sinking the poles in the wet concrete was the best way to go. Reason: from a structural standpoint the sunken poles offered much more rigidity on their own individual merit and even more as a unit. Poles in brackets would require a lot of side wall bracing not only in the corners but all along the side wall, not to mention diagonally in a horizontal plane where the trusses sit (as in conventional building practices). Also the mid sections of either eave wall would allow the trusses to pivot at the tops of the mid-wall posts---a good wind would push in the sides of the wall and not necessarily the corners. FBi Buildings in my second to last post uses a "system" of creating a mortise-and-tendon joint where the truss meets the post to make it rigid. I once seen a 3-story barn strictly used for hay storage that had to overcome this problem--they used crisscross diagonal bracing made of 1" round bars connecting in the very center of the barn's usable area--not practical for a pole building!
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