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NY BUCKS
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# Posted: 14 Jun 2015 12:59
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I am planning on setting a 22x26 cabin that is being built for me offsite. I have contracted an Amish gentleman to build at his place and bring in three pieces to my 50 acre parcel. Building will be constructed on 4x4s. It will be my responsibility to provide foundation for this structure to sit on. I first thought four rows of three sonotubes. Problem is a lot of concrete to mix by hand and getting them all level might be a challenge. My next thought was to lay out and dig the 16 holes 48"deep, fill bottom 6"or so with gravel and set PT 6x6 on top with concrete fill. From there noch 6x6 to accept 2x12 on each side. Any comments or suggestions?
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AK Seabee
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# Posted: 14 Jun 2015 14:23
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The sonotube only needs to rise just above finished grade. Simpson sells hardware to transition from the sonotube to your above grade foundation (4x4, 4x6, 6x6 ect....)
The benefit of concrete below grade is concrete continues to gain strength as it ages. Lumber will begin to degrade immediately (slow or quick depends on soil conditions).
You can treat lumber above grade to prolong its life. Below grade the lumber is left to its own accord.
If concrete is not an option due to access limitations there are other options including but not limited to pile driving.
A below grade wood foundation can still work just keep in mind that through the years it will require more intensive maintenance.
Just my two cents. Whatever your decision, good luck!
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bldginsp
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# Posted: 14 Jun 2015 22:45
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I have a deep seated personal prejudice against putting wood in the ground, so be forewarned. It just won't last. 20 years from now you'll have a near impossible problem on your hands. Yes it's a lot of concrete to mix by hand but you can hire laborers. Sure you can't get a concrete truck in there?
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NY BUCKS
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# Posted: 15 Jun 2015 09:17
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Thanks for the input.You guys reinforce my own concerns. I have actually mixed the concrete by hand to replace the wood post under the deer camp I belonged to 30 years ago. What a job, digging by hand under a building. A real PITA!
What size sonotubes do you think would be sufficient? I was thinking 12"? Should the hole be larger than the tube? Your input is greatly appreciated, this will be the last camp I ever build and would like it to outlast me
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grover
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# Posted: 16 Jun 2015 14:01
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I wouldn't even consider the posts in the ground. 12 inch sonotubes would work well. Leveling should not be much of a problem unless you are on the side of a hill. You could use the old fashioned water in a clear plastic tube method. Very cheap but very accurate.
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Don_P
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# Posted: 16 Jun 2015 22:48
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This might be a good place to continue talking about the lateral loads on the foundation, we have some dimensions to help with the thought process.
I've attached scans of a couple of pages that might help. Making an assumption that this will have a 12/12 and a loft. In most of NY it would be in the 110mph column. Wind perpendicular to the ridge would produce a lateral diaphragm load of 149 pounds per lineal foot from the roof and 135 plf from the main floor 284pounds per lineal foot X 26 lineal feet on that wall= 7384 lbs. Divide that by 12 piers= 615 lbs of horizontal load trying to overturn each pier as the floor diaphragm that they are all well connected to tries to move horizontally.We've decided that the ground is a poor brace to resist this force, it'll probably be mud the day the wind decides to blow that hard. The pier is 4' tall, assuming the footing isn't going anywhere, the connection between each pier and the floor diaphragm is seeing 4' x 615 lbs= ~2500ft-lbs of torque.
Now I don't know how many of you have torqued bolts till you break them or have run a bolt up to say 200 ft-lbs. If you're trying to run a couple of 1/2" bolts through a wood 2x12 for this... we're at 2500 ft-lbs. There is a 600 lb gorilla with a 4' cheater bar at every pier trying to turn his pier over under the house.
There's the load to be resisted.
Now if you were to triangularize a brace, go down 4' to the pier base, run along the girder 4' from the pier and run a diagonal brace, the load on the bolts at each end would be ~870 lbs, getting better, a couple of 5/8 bolts along the axis at each end would do it. Whatever the brace is made of it needs to take dirt and not buckle under an 870 lb compression end load, along its' axis.
That is one way.
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