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Hi

I was asked to build a small house using an old method of slipforming with concrete and stones. This seems to be a method that is growing popular among DIYers. Especially those with "green" principles in mind. Basically building a standard footer and forming up a concrete wall every 2ft high, adding stones and rebar. Obviously this is creating both horizontal and vertical cold joints. Some seem to say this is not a problem since the rebar help to make the wall "strong enough" for its intended purpose. Meaning the only factor to consider is making sure it is sealed off from the water. I ponder this and hope that someone here can give an expert opinion.

But that isn't at the core of why I am posting here. I plan to use 4" rigid foam EPS with this wall. I am into solar principles Namely the use of thermal mass inside the house. The house will be a single story with a vaulted gambrel roof. The potential problems of using a vaulted ceiling with solar principles is well known. So that's not important right now. But what I want to know is how thick to set the form for the bearing walls? I recently saw where someone placed thick foam sheeting in the middle of the form and poured cement on both sides of it. As well as using the stones on one side of the form. It led me to wonder if the foam adds to the structural ability of the wall? Or would I need to make the wall on ONE SIDE of the foam thick enough to hold the roof? Meaning that the wall on the other side is nothing more than being there for looks.

Other than for safety reasons, I would like to know this because I would prefer to make the interior side of the concrete wall the bearing wall if necessary to get it thicker for thermal mass. And then make the exterior side thick enough to suit the purpose of stone/concrete on the outside. What would make this work?

I would certainly appreciate any insight you may have!
 

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The foam is an effort to assist with thermal bridging, it degrades the structural integrity of the wall. The foam needs to be on the outside of the wall.

If you are applying stucco or something similar to the exterior, you will need to use this in each pour throughout the wall at every cold joint.

https://www.kossan.com.my/RubberDivision/rubber_rw.htm

It is not cheap, but it is effective in preventing water penetration. Also, slip forming is very expensive from a form standpoint on anything but a straight wall. How do you propose to build the form?

Rubble concrete is un-reinforced concrete, don't waste the money on rebar because it will also decrease the structural integrity of the wall.
 
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