The Carriage House
An Earthbag/Papercrete/Steel Quonset Vault
I have designed a garage/workshop on my property. I wanted it to blend in with the architecture of our house, which is an earthbag/papercrete combination of domes, vault and planes. It also needs to be inexpensive to build, conservative of energy input for heating and cooling, and fairly quick to build. The idea I came up with was to erect a steel quonset building, which is essentially a vault, covering it with earthbags filled with crushed volcanic rock (like our house) and then use a final plaster of papercrete to protect the bags from the sunlight and abrasion.
I located a new 34' X 16' steel quonset building that was sold disassembled for $1900 delivered. I realized that if I raised it up 4 extra feet, I could build a loft in it, so that is what I am doing, using a double row of earthbags on either side to support it. The bags of volcanic rock are recycled form a house project that I helped demolish several months ago, so the whole thing should be quite inexpensive. I'll be making the end walls out of more bags, wood framing, openable windows and big garage doors.
At the point of connection between the bags and the steel is a buffer of 2X10 wood with steel angle brackets to which the steel ribs are bolted. Once this wood gets embedded with the bags going over the vault and eventually papercreted, the whole thing will become rather monolithic. The wood is also pinned to the bags with half inch rebar to further anchor the quonset. To make the whole thing more rigid and to be able to support the weight of the bags, there will be either cables or wooden floor joists for the loft tying both sides of the vault to each other at the point where the arc begins (the spring line).
So far I am pleased with how it is all coming together. I raised the first section of the quonset by myself on a day that was windier than I liked, by stretching a rope between the two trees and running a cable from the top of the roof section through a pulley on the rope, and then winching the section to a vertical position. Writing this is much easier than it actually was, because the steel was much less rigid than I expected and was sort of flopping around as I tried to raise it. I really should have had a couple of assistants guiding it up on either side, but I persevered I finally got the thing to stand on its own. Once I got it bolted and tied down, it was relatively stable. The second section was erected one piece at a time (each section is composed of five pieces). Now the vault is sturdy enough for me to climb around on it with confidence.
Each arched section is composed of five pieces, and there are 17 sections, so it entailed a lot of ladder work to bolt the thing together one piece at a time. Fortunately I figured out a way to tighten each bolt from one side, using a pair of vise-grips to pull some friction on the little neoprene washer to keep the bolt itself from just turning. You can see from the photo that I have started to stack earthbags (filled with crushed volcanic rock, or scoria) up the side of the metal vault. I put a liner of plastic between the bags and the steel, not for moisture protection, but to protect the steel from the possible corrosive action of the the rather acidic scoria. I will be keeping the bags covered with tarps until I have a chance to papercrete them. So far I am satisfied that the whole concept will be fine structurally; only time will tell, since this is definitely an experimental structure.
As you can see from the picture, I have begun to plaster the earthbags that cover the steel quonset vault with papercrete, and am rushing to beat the deep-freeze of winter at 8,000 feet in Colorado. I am attempting a single application of the plaster, with a papercrete mix that has a lot of sand in it to give a harder, more durable surface that will be more resistant to fire and will shrink very little. I lined the earthbags with 2 inch chicken wire before applying the plaster, to resist cracking and provide a more monolithic coating.
You might notice that there is a board mounted just outside the bags above my head. This is a retainer (2X6) that is bolted all the way through the bag wall and the steel shell, right at the point where the vault starts to curve inward. This retainer will keep all of the bags that are stacked above it in place, so they don't topple the vertical portion of the wall.
A considerable effort was made to bring this project to a point where it could be left for the winter. This meant installing all of the loft joist/tension supports (2X10 lumber) on the inside, stacking all of the earthbags filled with crushed volcanic rock over the steel vault, and covering the whole thing on the outside with papercrete. At a certain point I realized that doing this was beyond my personal ability, given the time constraints. Fortunately I encountered a couple of very hard working Mexican-American roofers who were willing to spend two weekends helping me do all of this. I learned several things from this experience, not the least of which is that doing this sort of work with a crew can go very fast and efficiently. The best news from doing this is that the basic concept is working! With all of the weight of the earthbags and wet papercrete covering the quonset building, there was no straining or deformation evident. As the papercrete cures, the structure will just get stronger and stronger.
The photo shows the front end, which was created with wood framing and siding materials. Most of this wood was either recycled from nearby building projects (taken from the dumpster), or bought as remnants. The cedar lap siding actually represents four different styles, so the fascade has a rather patchwork quality. The door and windows (except for the glass blocks) were all recycled as well.
I am quite pleased with how the steel quonset/earthbag/papercrete portion of the structure is working. I finished this part last fall, so it has wintered over with no apparent problems. Now that the heat of the summer is upon us, I can testify that the interior space is remaining deliciously cool, something that would not be expected with an un-insulated steel building. I believe that this method of construction has tremendous potential for residential use; it could even be earth-bermed successfully if desired.
The interior of the shell could be finished in a variety of ways, or even left with the steel showing, as I intend to do with this workshop. Cloth material could be draped over it, sheetrock could be scored on one side to allow it to curve to the shape of the vault, or wood tongue and grooved siding could be installed, to name a few possible surfaces.
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