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Post footing design. W/ tires and compacted gravel

 
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Hello! Its my first post here, but have been casually perusing these forums for years now. Planning on building a little house in the Arkansas delta this year. It's a very wet and muddy region and I've been considering my options.  My rough plan currently is a mix of round wood and milled timber framing with mixed materials for infill. Would like to use straw bale, but hesitant because of the environment and it will likely not be occupied full time. I would also love to have an earthen floor to help keep it cool, but am also quite hesitant because of the moisture issues. Here's a little rough diagram of a pier design I've come up with for the post: using old tires and compacted gravel, rebar driven into the sub soil, tied in with and poured cement. I'd love to hear y'alls thoughts thoughts on all these things. Thank you!
16137863295166559006822570280819.jpg
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gardener
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Welcome to Permies!
That's a nice looking sketch.
I love the idea of tire foundations.
Your pier reminds me of something called mechanical concrete.
I think I would be inclined to cut one sidewall out of each tire to make packing in the gravel easier.
I might drive some rebar through the remaining sidewall for increased stability.
If its available, you might want to use basalt rebar.

I would want to replace the concrete pad with a flat stone if possible.
No matter what is used, youll want a moisture barrier in-between the post and pier to prevent wicking.
Consider leaving the rebar stick up through the concrete pad or stone as a "pin".
This allows you to drill a hole in the bottom of the post and set it over the pin.
The combination will prevent the post from moving sideways off the pier.
 
pollinator
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What is your thinking behind the details you have drafted?
How big, is the small house?
 
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Location: Cocolalla ID
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i like the train you’re on too. I have been making similar plans. i’ve considered pole barn style structure with straw bale infill and tire foundation. I will warn of experience with condensation on floors when they are directly linked to the ground. that has just been my experience.

i’ve been thinking about a good way to anchor the posts if they were on the foundation rather than in the ground. Do you think a fiberglass rod driven into foundation and then up through the concrete and into the bottom of post would work well? figure you could the. pin through it for hold down if you wanted. Seems less likely to sweat inside the post than steel.
 
Dustin Egan
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Thanks for the replies! I'm leaning towards cement vs stone just because of availability in the area. Theres no natural stone to be found so I would have to buy them. I was considering having the rebar come up through the cement as a pin(s) for the post. But was leaning more towards setting in bolts to use some sort of bracket. I'm going to be doing most of this work by myself and raising the post on to pins seems much more difficult than tieing in to a L style bracket with bolts. I was hoping that moisture wicking might be minimal as the tires and gravel shouldn't draw up much moisture. What kinda moisture barrier would you recommend between the concrete and the wood?

The structure is going to be about 10×20. I'm leaning towards an internal timber frame with a metal roof. A raised deck flooring.  And bousillage infill for walls.  Is it possible/ wise to build the bousillage up from the deck?  Or should it have a Foundation of its own?
 
pollinator
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Make sure you're not spending a dollar to save a dime. Yes, tires are free but will hold 2-3x more concrete as a properly sized sonotube.

DEFINITELY use a bought post base. They include a spacer to let the post dry through the end grain and hold the post DOWN so a hurricane doesn't pick up your house.  

That uplift protection is what is missing in your original design.

Your rubble piers should work to a point, but I wouldn't go too high. Not sure how to easily add hold down pins and bracing to them. They would be great for a shipping container where you aren't worried about lift.
 
John C Daley
pollinator
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A big advantage of inserting the treated posts into the ground is stability.
Cross bracing may not be needed.
I use many oif them, I drill a hole 2-2.5 times the diameter of the log/ pole and down about 4 feet.
I then backfill with concrete, not cement.
I often use steel poles because they are lighter and easier to use.
If the correct treatment for the poles is used, they will last many years.

In terms of flying shipping containers, I have read here that it can be an issue.
 
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      Howdy Dustin,

      This is a great topic, one I wish someone would have given me their thoughts on. I've built a post and beam Hogan style cabin. It's lovely except for one part, in retrospect, that I would do over to be completely sure of its longevity. I did the PSP technique on all the vertical posts which as it stands, is I think, worthy of consideration, however, in 20 more years I'm not sure what the state of my logs will be. I'm speaking to my particular situation mind you. Therefore, in retrospect and in my opinion the most straightforward way to ensure longevity of your building's vertical posts would be as earlier posters suggested, sonotubes with the strap to tie everything down, plus one or two more things.
      I have studied and taken classes on things like cob, and most alternative architecture vernaculars, including a building an earth ship for a few days and while those ideas are brilliant and create lovely homes, there are some things that perhaps on the face of it which should be considered and that's difficult to do in your sitting room. Here's what I have gleaned as a straightforward methodology to create a strong wall/foundation connection that will not rot. First, and beginning in Mother Earth, we need to prevent frost heaves, so we must put our foundation down as far as the frost line. Second, there must be a barrier to water which can be solved very easily by a sacrificial block and/or a piece of garbage bag. Third, the structure should be tied to the foundation so, it cannot shift or "blow off". Fourth, other than a problem with the earth being too soft and your structure sinking, at first glance I think that covers it.
      My suggestion, for your consideration then is the following: Sonotube to the depth of frost, with a piece or two of vertical rebar and proud of grade with a strap to secure your post to. On top of the concrete, a sacrificial block say one or two inches thick with a piece of plastic between the block and the concrete. The post goes on top of the sacrificial block. To review, you now have no way for water to enter your vertical post because of the plastic and sacrificial block which you can replace if it seems to be rotting. Frost heaves will not be possible and you can fill the sonotubes easily mixing concrete in your wheel barrow. Nice and low tech, except perhaps for the augering.
       One last point, depending the level of ground water in your area and the season, if its high enough say in Spring when the snow melts, the voids in the gravel will or can fill up with water, (the path of least resistance and all that) and possibly freeze in cold weather. Of course, after a few years it will all silt together if your don't use fabric etc. To sum up, for the kind of structure you describe, you might want to consider the above. Good luck on a worthy project.  

       Thomas

       Mitama farm
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