Foundation

I have finally made a decision on my bale foundation, I'm going to do a rubble trench. Lets hope I made the right choice.

My foundation needs to have many functions. First it needs to get the bale wall away from water. Water damage can be detrimental to a bale wall. If moisture is able to get inside the bales the wall will rot from the inside out. This is one of the reasons I cannot just put the straw bales directly onto the ground. The next function of my foundation is going to be to keep water from seeping into my house. I want to have my floor be in direct contact with the earth in order to take advantage of the thermal properties of the ground. If I do not have a proper foundation my floor will be cold and wet. I need my wall foundation to provide a water and thermal barrier between the outside ground and the inside ground. The last function of my foundation is to provide stable support to the bale wall. The reason I listed this function last is that the way that my foundation can do this is determined by it's other functions. I need some sort of wall around the perimeter of my house to keep water out and the support of that wall needs to go below the frost line.

The top most layer of the earth is very soft. it is made of lightly compacted decaying organic matter. I would not want to just put a foundation wall on this because it would sink. On a rainy day I can depress the soil with my body weight, I can only imagine what a whole house would do. I want my foundation to be below the fluffy top layer, sitting on more compacted soil. This is where the frost line comes in. If i dig a hole 1 foot deep I will probably find some well compacted soil, but I might not want to just stick my foundation on it. If in the wintertime it gets cold enough to freeze the ground below that one foot deep hole my foundation will raise up, and could cause my walls to fall. I believe this is called ground heave, but don't quote me on that. When the water in the soil freezes it expands, if there is something like a concrete pier sitting on top of the freezing ground it will move around with the expanding soil. For this reason I want my foundation to sit on compacted earth below the level that will freeze in the winter time. This is called the frost line. In richmond the frost line is some where around 18", so my foundation is going to be at least 24" deep.

Finally, the ruble trench. A ruble trench foundation uses a concrete beam on top of gravel filled trench that goes down below the frost line. The idea is that the gravel will not compact like soil and will not retain water and therefor will not heave. The reason that I choose a ruble trench over a poured concrete foundation, which is a more typical method of building, is that concrete has high Embodied Energy. This roughly means that a lot of energy and resources are required to make concrete, and as a result I would like to use as little of it as possible.