11 / 02 / 2020
“How are you supposed to know when the earth inside the tires is compressed enough?”
“Well, if the tire is squishy it needs to be compressed more”
Its been a goal at Bonsai to one day have the opportunity to design a home modeled after an Earthship. An Earthship was pioneered by Architect Michael Reynolds as a residence that utilizes passive building techniques to create a comfortable, incredibly efficient building. Earthships have been a standard in developing on site energy creation, water recycling, and food creation. They are, in many ways, a self-contained ecosystem.
Last year Bonsai was approached by our clients to design a new Earthship inspired home outside of Pueblo CO, where they had a unique piece of property near the border of the National Forest. The house is designed to be a three bedroom, two bath program with a spacious kitchen and living nested in the middle of the spaces. The north side of the home is built into the hillside to help with thermal regulation. This tire wall acts as a retaining wall for the earth behind it. A interior south side walkway creates a greenhouse area that runs the length of the house. The southside greenhouse area utilizes the angle of the sun and a large thermal mass floor to assist in warming the home. Fresh air is brought in through the north side of the home where earth tubes are buried in the hillside and over the length of the tubes air is cooled by the earth via conduction. Warm air is pulled out of the house via natural convection from the greenhouse, while simultaneously pulling cool air through the cooling tubes. Large cisterns buried in the hillside are used to capture rainwater and feed greywater systems. The greywater is then used in the planter boxes or bathrooms. After Bonsai designed and assisted with the permitting process of the new home, we were invited to join for a build day.
We arrived on what we were told was a cooler day, high 80’s and cloud cover. The crew consisted of a few hired hands outnumbered 3 to 1 by volunteers. People had come from all over the country after the clients had sent out the request for help, taking the opportunity to work on a unique build. It was one of the last days for tire pounding, the last few rows of tires before the top of plate height is reached. We hauled tires to the top of the wall where they were dry fit, offset and setback from the row below, and anchored with screws to the tire underneath. Tops of tires were constantly checked by laser as the tires were filled and compacted. The compaction of the tires is not rocket science, but incredibly labor intensive. Each tire, roughly 30” in diameter easily took 10- five gallon buckets of earth when compacted. So it went, set tire, check location and height, fill with dirt, hammer, hammer more, fill with dirt, check location and height, hammer…
As part of the trade for volunteering, the clients provided lunch and dinner for all workers and volunteers throughout the build. During lunch that day we got a chance to talk with a few of the workers who had previous Earthship experience where they explained the science and technique behind building these unique homes. One of which was how we are supposed to know when the earth in the tires have reached the appropriate psi to conform to structural standards. The general rule of thumb is that when pressing the outer walls with your boot it no longer deforms to the interior. This along with compacting the earth to the point where it must be pick axed to break up typically serves as the standard for compression strength in the tire wall.
We stayed on wall duty until the end the work day. Dusty and feeling accomplished, we began the trip back to Denver.