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I'm building a 10'x16' shed/dry cabin. I am planning for a pier and beam foundation with 6 piers. It's way off grid and pretty small so I'm hoping to not overbuild and I want to use EZ tube pre cast piers without the base sections. Going from 15" diameter holes I can drill with an auger up to ~23" diameter holes seems like a big lift. Question: will my piers adequately support my building without footings (base sections)?

https://icc-es.org/report-listing/ESR-5035/

  1. my location is loam soil, likely around 2,000 to 3,000 psf capacity
  2. my piers will go 24" below grade (below the 18" frost line specified in code)
  3. the building won't be permitted, I just want it to work
  4. the piers will have 6"x6" vertical posts to support the beams (not pictured)
  5. probably 2x10" floor joists to support the unsupported 10' span

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Just a rough calculation of your 15" diameter piers yields a weight-bearing area of 1.23 sq-ft. So at 2000 psf that gives a load capacity of 2454 lbs. Your 6 piers will then be able to support 14,726 lbs.

What is the expected weight of the building + contents + any external loading like snow?

If that falls under 14K lbs, then you should be good. If not, you will either want to go deeper to more supportive ground or look at upping the size of your piers.

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  • Thank you.The holes I dug with the auger are 15" diameter but the ez Crete piers are 11". Not sure how to estimate the weight of my building but sounds like I have a lot more research to do. Was hoping for a simple answer but in engineering there never is one. May 3, 2023 at 2:45
  • It's not that hard to estimate the weight of a building. You should be able to get a total "board-feet" of lumber from your supplier (or calculate it yourself) and using data from lumber suppliers calculate the approx. weight. Then add things like roofing, wall coverings, furnishings, etc. What are you going to store in the building? Vehicles, equipment, living space? Add those up. But at 11" you're considerably lower than at 15". You can do the numbers yourself but the problem is that the sq. footage of the pier's bearing surface goes down with the square of the diameter.
    – jwh20
    May 3, 2023 at 11:51
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For a technically correct answer to your question soil tests and calculations would have to be done. However, you want the simple answer and that's understandable.

I had an inspector check pier holes dug for the base of a 2 story addition. He used a 3 foot section of #5 rebar with a T-handle welded at the top ( very high tech).

He said the holes were deep enough when he could not push the rebar deeper than 24" into the soil at the bottom of the holes.

That was good for the county. My brother-in-law who was assisting me and is a geological engineer, said that it was a pretty simple test that probably was correct.

If I was building the cabin, I would do the rebar test and sleep good at night.

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