Thank you all for your widely varied responses to this thread. Wow. Just when I thought that a technical thread would draw a rapt audience.....
Special Thanks to Tanvil for his inclusion of the e-book on Strawbale construction. I have read this in the past, and found it to be a very worthy guide to building with bales. We should all treat this as the detailed guide, and I will focus on the poor mans methods.
So, on to the thread subject:
Chapter 1: Strawbale construction.
I am going to skip most of the past experience, and concentrate on the fundamentals of building a very low cost strawbale domicile that will probably outlast three generations.
For simplicity sake, I am going to confine the building type to a simple loadbearing design, where the roof structure bears directly on the bales that comprise the wall structure. With that in mind....
There are many types of foundation that are suitable for strawbale structures. For our purposes, the foundation needs to provide the following:
1. It needs to carry the load of the structure like any other foundation.
2. It needs to be cheap, and easily constructed without a great deal of skill.
3. It needs to elevate the structure at least 6 inches above grade.
4. It needs to incorporate the ability to have "tie-downs" run through it that strap the completed strawbale wall to the foundation.
5. It needs to be suitable for the building site, and it needs to shed water, not retain it.
Given these needs, I have focused on a centuries old method that has been used even by noted architects like Frank Lloyd Wright. This method is called "Rubble-Trench".
A Rubble-Trench foundation is simply a trench, between 2-6 feet deep depending on soil and grade, and environmental factors such as annual precipitation and temperature. The Rubble-Trench should end up being 25-50% wider than the finished wall that will sit on top of it. The width of the Rubble-Trench is determined by factors such as soil composition, shear resistance, seismic activity, and wind load.
Practical example of a Rubble-Trench foundation
Location: Grass Valley, California.
Structure: Ranch House.
Grade: 6-12% incline.
Soil: Silt and sand
Average Temp: 68f
Low Temp: 21f
High Temp: 110f
Annual Precipitation: 8-10 inches
Average wind: 4-12 mph.
This project was both my first Strawbale, and my first Rubble-Trench foundation. According to the best information I had, the composition of the rubble trench is based on all of the above factors. So, my design started with the dimensions of the strawbales that we intended to use. These measured roughly 16-17 inches high x 23-24 inches wide by 42-47 inches long, weighing about 75 pounds each. Since the bales were being sourced from a family friend of the property owner, we were able to ask a number of important questions before the straw was ever baled. We learned that the bale machine operator (a contractor) had a great deal of control over the end size and density of the finished bales. We also learned that we had a lot of choices available for the tie material as well. An extra $100 for our choice of tie material, and an extra $300 to the bale machine operator and crew provided us with very tight, very uniform, and very heavy bales of rice straw.
For the purposes of design, and getting the local building inspector to relax, we made the trenches 38 inches wide, and a minimum of 48 inches deep. Since the building site had a significant grade, we decided to top the rubble-trench with standard reinforced concrete caps, poured in place, and anchored to the rubble with long rebar j-bolts, tied into the rebar reinforcing in the caps.
We began filling the trenches with 1-1.5 inch river rock, poured over drainage fabric which extended all the way up to the top of the trench, this layer was filled to a depth of one foot. The next two feet were comprised of a mixture of large (6-10" stones, broken concrete, "rubble", etc.) infilled with sand-gravel to lock the rubble in place. A 4 inch deep bed of the sand-gravel was poured over the river rock and tamped / vibrated to allow it to settle into the first layer. Once the trenches were filled to within 6 inches of grade, the forms for the concrete cap were built, and the cap poured. The finished product created a 36" wide footing for the strawbale walls to rest on.
Next, we will discuss an important set of concepts:
1. Pre vs. Post Apocalypse construction.
2. Permitted vs. Non-Permitted construction.
3. Good Enough vs. built to last construction.
We can condense these concepts into When to build the structure.
Pre Apocalypse, Permitted, Built to last construction is what you essentially have to do now, while there are laws in play.
Post Apocalypse, Non-Permitted, Good Enough construction is what you do when there is no law in play.
I will short hand these into the following:
Stay tuned for the rest: