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poles in the ground vs. concrete footings with anchor
We are building a 30'x 50' pole barn with 10' open side awnings on each side next summer in Iowa. Some barns are built with the pole in the hole, set on a concrete footing at the bottom of the hole. I saw another design, where they poured a 4' concrete footing in each hole, and then set a deep anchor in the wet concrete with flanges to bolt to the pole. No rotting this way, but is it strong enough? Plan on heating to 55F in the winter. Do I need a vapor barrier or foam under the slab?
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poles in the ground vs. concrete footings with anchor
Chris: I too grew tired of watching supposed "Lifetime Poles" rotting off at ground level after less than 20 years. In 1981 we built a 72X72 pole shed. I had a basement co. pour a footing and wall to above grade level then we fastened the poles to the top of the wall using salvage grader blades. With todays cost of concreet and labor this might not be a good option today. I can't think of any reason that concreet piers with perhaps a heavy angle iron set in the concreet to maybe 4 ft. above the pier to fasten the pole to would'nt be strong enough. Perhaps auger an 18 to 24 in diamater hole and just pour the concreet in avoiding the cost of forms. I'm far from being an engeneer, but my building is standing just fine with no rotting poles. Others may have better ideas too. Frank.
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poles in the ground vs. concrete footings with anchor
Pressure treated poles will rot off? I had not heard this. I have 40x40 with concrete floor. in clay. anything to be done now other then cross fingers?
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poles in the ground vs. concrete footings with anchor
BigBru: The old poles that were boiled in creosote before creosote was restriced by the Gvt. seem to never rot off. I've got an old corrgated tin shed on the farm that must have been built in the late 50's with genuine creosote poles that still don't show a sign of rot. I really don't know for sure what the preservative was that was used after that, but I put up a pole shed in 1969 using the "New" square poles with the then legal preservative, and within 20 yrs most every pole you could kick the toe of your boot thru at ground level. We were asked to build some playground equipment a few years ago at the shop, but after checking codes found that the "Green" poles and lumber were not legal to use because of arsenic in the preservative. Frank.
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poles in the ground vs. concrete footings with anchor
In a way, anchoring poles to the top of a footing, then framing the structure like a pole building is mixing two different construction methods. The 4' deep pole serves two puposes in a pole building; it gets the bottom bearing surface down below the frost line, and it also gives the structure lateral stability. Most pole structures use girts that the siding material is attached to. The shear transfer from the girts isn't the same as it is if the siding is attached directily to the poles, and there aren't as many. The 4' embedment of the poles helps stiffen the structure for lateral loads (wind). If you are using poles on 8' centers on top of the footings, some lateral bracing should be added to the walls to help give the building lateral stiffness.
As far as vapor barriers and insulation, there is a recent thread with a lot of discussion about this. If you are heating the building, a vapor barrier is recommnended. Insulating under the slab can be beneficial for retaining heat, but can reduce the bearing capacity of the slab based on the compressibilty of the insulation.
Any time lumber, even treated, is in direct contact with concrete, deterioration of the wood is possible. Concrete conducts water, and the lumber acts as a wick. The lumber will stay moist at the concrete almost all the time. The best thing you can do is isolate the two materials, even if you mount on top of a footing. Steel base plates with pole sockets work quite well.
Add some lateral bracing to the walls, base plates at the posts, and a vapor barrier under the slab and you'll have a good building.
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poles in the ground vs. concrete footings with anchor
That method would be strong enough. The only concern I would have is getting them set in a straight line. I would
set up a string on stakes beyond your builing corners and
use the galv.brackets Beagle referred to. They work well for 6x6 posts. I would just stick a 6" bolt through the bracket into the wet cement. Alignment is crucial.
I would also throw some 1/2 " rebar into those footings
I criss cross mine with 3-4 pieces. The last one I did I used "Elaphant feet" with sona tubes. It is a funnel shaped piece of plastic that the sona tube sets into. So that you can pour your footing and tube at the same time. The shape of them(upside down funnel) prevents frost from lifting them.If you are interested I will get the exact name of the product for you.
I am of the school of thought that foam under your slab is a good idea. One winter you may decide not to heat it,I believe this will keep the frost from getting under your slab and heaving it. The poly under your cement serves another purpose as well as the vapor barrier, it prevents
the floor from drying too fast when poured. The longer you keep it wet the harder it will get. When able I spray with a hose daily for a week.If it hot weather,get you roof on first. BTW 3500lb cement is only a few dollars more than 2500lb mix.
Good luck
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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)
Link:
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poles in the ground vs. concrete footings with anchor
If you insist on putting posts in the ground, there is a company that makes a boot that fits over the pole and sticks up about 1' above grade. I believe it is made from some kind of high density poly product that they use to line landfills. I think the name is Post protector. I opted out of the wood altogether and there is not one piece in my building, Try looking at Miracle Truss or Kentucky Steel for an easy do it youself, and it looks like a pole barn, or any one of the I-beam type. I went with I-beam for cheaper cost but kept a high pitch roof so it fit with my house. Many I-beam companies try to sell you the industrial looking low pitch roofs. Sorry I don't have any pictures posted yet, I'm working on finding them.
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poles in the ground vs. concrete footings with anchor
Around here the preferred method of setting poles in the ground for buildings was to set them into stone cairns.
Basically they would dig a hole a little deeper and larger around than the pole, then put one large flat stone in the bottom of the hole and some very small stones (gravel today) on top and stand the pole on that, then backfill around the pole with small stones, gravel and sand.
The idea was to create an area of very good drainage around the pole. If the pole stays dry it won't rot.
It would never fly today, but it used to VERY common for people to dispose of their used motor oil by pouring it around the base of all the poles, it soaked into the wood and saturated the soil making them water-proof.
Best of luck.
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poles in the ground vs. concrete footings with anchor
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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