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Post in ground techniques

 
author and steward
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Josiah made a video about what we do these days

 
pollinator
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I know this is about post in ground, but I was in China a couple of weeks ago and looked at wood construction which used no nails.

The wood pillars just sit on stones that hold them off the ground.  Friction holds them in place and of course they have very heavy tiled roofs to increase the friction.  The wooden bracket system transfers the load from the roof to the pillars.
The wood was also painted with something to prevent insects eating the wood.



This is the Piyun tower on the Ancient City Wall of Zhaoqing built about 900 years ago.  It was renovated in 1989 but I don't know to what extent.
I'm guessing the pillars held by friction wouldn't withstand the lateral forces of an earth bermed structure but can anyone make an intelligent guess?  Maybe it would just need some cross bracing at the right points?

Anyway, the point is, do we really need the posts in the ground and can we not just place them on top of the ground?
 
Graham Chiu
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I was thinking about precedents again.  A wofati is like a cave opening so what do miners do?

It seems that they also don't bury the timber props that support the walls and roof.  They can dig a 25 mm area for the base of the timber prop so it doesn't slip as they raise the prop.

https://www.engineeringenotes.com/mining-technology/mine-supports/types-of-mine-supports-timber-iron-and-steel-rock-mechanics-mining-technology/51784

(b) Roof Height of 2.5 to 4.5 m:

There are two methods:

(i) The position of the bottom end of the prop on the floor corresponding to the place in the roof to be supported is marked by a plumb bob suspended by a bamboo. The prop is held upright by 2 or 3 timber helpers. The timber man standing on a high stool or a ladder places the lid and a wedge is hammered on a position.

(ii) The above method requires a stool or a ladder to be carried from place to place for prop erection. The more convenient method is- a lid is attached to the prop by nails and a hole is made nearly 25mm deep in the floor where the bottom end of the prop is to remain after erection. The prop, laid on the floor with the bottom end in the hole, is made upright, the hole preventing the prop from slipping.

The prop is held in position by timber helpers’ and one timber helper levers up its bottom end by a crowbar bringing the lid in contact with the roof. A wedge is then hammered between the prop and the floor to tighten the lid against the roof.

 
pollinator
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Following this thread as my goal is to one day have a wofati/Oehler style house for ‘retirement’... even seems like the wife is starting to buy in a bit more and talking about some rural land being a good idea that she supports. Planning to stay in Missouri, but move further South towards the Ozarks/Springfield area eventually and would love to get some permie neighbors. I was wondering though, if I can plant or find a lot of black locust, how much would that change thinking about rot-resistance of posts?
 
paul wheaton
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Black locust will be far more rot resistant.  At the same time, you are in an area with more rot.  

I suspect that I would probably skip the treatment with black locust.
 
Graham Chiu
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Here's a video of a Korean hanok construction.  They also place the posts on stone.

https://www.youtube.com/watch?v=IPhAPa8wlCQ

At 2:40 they drop the post onto the stone support which looks like it's covered in salt presumably to give more friction, and stop water creeping up the wood?
You'll note the absence of rebar to hold the post in place!

Unclear as to what is happening at the end of the video.  Looks like they deconstructing the brick walls.  Maybe the builder was a cowboy as the information with the video suggests?
 
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I just mix a nice cob with lots of straw or woodchips and poor in hole around post. Works great in my climate.(desert/mountain). Also experimenting with cob foundations .
 
steward
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For all those that still need an answer to the old question: "how to prevent wood posts from rotting without using bad substances?', here is an answer from Paul, in the form of a cute video. Enjoy!

         
 
master steward
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That's a great little video! Clear, concise and made total sense to me, living in a ecosystem that can rot just about anything in the wet winters we have! The little project I want to do will be difficult to build a 5 ft eve for, but using slope and rocks as a intercept might be enough to slow down the rot process acceptably, as it isn't a house.
 
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Would charring the postal before encasing them in crushed rock further extend  the life? Or is it entirely unnecessary?
I've become a char crazed wood worker of late and have no aversion to charring the wood prior to construction if it will help extend post life or strength through case hardening.
Overall. Lov9ng the simplicity of simply filling hole with crushed rock
 
Rocket Scientist
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Planting black locust is a long-term proposition. It will probably be at least 20 years before you have large enough heartwood for structural purposes. The sapwood (most recent several years of growth) does rot fairly quickly in moist conditions. That said, I would always advise starting some if you don't have any, as it will be useful for smaller projects within 10 years, and will sucker and coppice readily to make a perennial source of dense firewood for an RMH.
 
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Liv Smith wrote:For all those that still need an answer to the old question: "how to prevent wood posts from rotting without using bad substances?', here is an answer from Paul, in the form of a cute video. Enjoy!

         



Is this the most current method being used & how long has it been tested? What species can you reliably use with this method (pine? or does it need to be something more naturally rot-resistant?) Should the bark be peeled or left on? Thanks for any extra guidance.
 
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T Phillips wrote:We did what Ty and Don outlined when we built a 6' fence in Westcliffe, CO. Because this was to enclose a 1 acre site and because we are not spring chickens, we paid a crew with a small machine to auger the post holes 8" in diameter and 4'- 5' deep. We then put 3/4" angular rock (gravel) in the bottom of the holes and placed the 10' tall, 4x4 cedar posts in them. We then added gravel and tamped 4-6" lifts of gravel into the holes, keeping the posts centered. The fence has held up beautifully for 10+ years. It was one helluva lot of work, but it was worth it.




@T Phillips, how are the post now?
 
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I'm looking to build an earthsheltered PSP style building. Perhaps a dumb question, but if I'm already below the frost line why sink posts at all? Couldn't one use sill beams instead? I'm guessing that in an Oehler building, sinking the posts helps to resist the pressure from the earth but if the sill beams are sufficiently squared and shored and the posts are tied into the sills very securely why would sinking posts be preferable? With sill beams I could almost eliminate direct ground contact.
 
master steward
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Hi Nathaniel,

Welcome to Permies.

You don’t state your location.  In northern MInnesota, I have seen houses and barns successfully floated on the surface of the ground.  These were otherwise conventional stud wall construction.
 
Nathaniel Bouman
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Yeah, I guess my query is mostly about underground construction. Most of the structure would be below the frostline so I'm a bit confused why sinking posts into the soil is that necessary.
 
steward
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I like the way you're thinking Nathanial!  I suspect the post frame style is just easier.  Doing a sill would be more dependent upon some skill at joinery.  I don't think most conventional post and beam joinery is anticipating many tons of side load.  A series of big posts in the ground might resist the lateral load easier than sills?  Or you'd need a number of big floor joist beams to hold out the bases of the walls once you get away from the corners.

I can see how this would be very doable and I love the idea of eliminating ground contact
 
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There are thousands of years of history from our ancestors to learn from on this subject.  Look up japanese timberframing.
Putting posts in the ground is picking a fight with nature, and nature will win.  And its completely unnecessary.  

Q. What is a reason to put the post in the ground?
A. Shear strength to help resist the pressures of the earth wall.

Q. Why is the earth putting pressure on your wall in the first place.
A. Because you designed your earth wall vertically.

Q. Why did you design your earth wall vertically.
A.

Q. Might there be a better geometry to design your earth walls that wont put pressures on your posts.
A. Yes

I like a lot of oehlers building vibe, but there is lots of room for improvement that would fix the rot issues and still keep the same building vibe of using free materials from the land.  

Learn from the past, wood on stone, above the ground, big overhangs, get the water away.  
 
Devon Olsen
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I've been thinking along the same lines as far as not building vertical walls.
My thinking is thus:
When we build an earth sheltered wall, we are, in essence building a retaining wall into our structure.

Retaining walls have tamped crushed stone foundations built into the earth a certain depth based on wall height. The tamped stone is also extended up the wall some distance on the earth side to increase drainage in the event that water infiltrates near the wall.

The wall is not built vertically because if the ground causes even the slightest shift away from the retained earth, gravity immediately begins to work against the structure, thus the wall is built at an angle into the slope, approx 1-3 inch for every foot of rise. So a 12ft tall wall should slope 1 ft into the earth from the base of the post.

in a wofati, this both increases the shear strength of the walls, and if done right, i beleive it would work to increase the feeling of spaciousness in the structure.
 
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