Jul 6, 2012 0
Earthship Build. Day 5.
Updates thus far have been from a mobile device; thus the content has been curt. Now I write from a full-fledged machine.
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A recap of construction techniques from the build:
- Site was assessed for house location before crew arrived. Re-bar was set for corner posts and strings were laid down to demarcate the corners of the structure, the centers of the U-shaped rooms, etc.
- Rammed-earth (pounded) tires were laid down to start the first course (layer) of the rear part of the structure. Tires are placed by following a pre-determined distance from the architectural drawings, measured from the center post of the room to the outer wall of the tire. For example, the first room we worked on had an 8 foot radius, so we measured 8 feet from the center re-bar in the room to each tire on each course that we laid down. Each tire is checked before and after pounding such that the radius curves evenly around the room. Tires are selected carefully for their size. It is wise to select tires of the same height when laying on their side with each course, as consistent sizing will allow each course to lay flat, so that the stacks remain level. This is easily done by reading the tire dimensions printed on the side of the tires. For example we commonly used 235/65 R16 tires. [Size guide] This would mean we would keep the first number (235) constant with each course. The second dimension (65) would refer to the sidewall depth. Larger numbers would indicate large profile tires, which are preferable to their low-pro counterparts, as they allow more dirt to be pounded into the tire. The final dimension (here =16) designates the diameter of the wheel (here 16 inches). We also aim for consistency here, as it keeps the courses in a consistent form. Tires are pounded exhaustively and take an enormous amount of dirt to fill. We line the bottom course with plastic before filling, and each additional course with cardboard before filling. First fill with dirt by hand, then pound the sidewalls with a sledge, until the sidewalls bulge. Then fill the center and pound. It might take 15 buckets of material to fill a tire. They become extremely heavy. Level each one and recheck their distance from the center post before moving onto the next tire. Be sure to alternate tire placement in the courses to ensure structural rigidity.
A note about the tires – these are all waste tires. Typically these are a liability and tire shops have to pay to dispose them. They are either burned or take up space in a landfill after their useful life. This way a waste-stream is diverted into a useful structure. The tire walls provide structural support and thermal mass to help keep the temperature stable inside the home.
- As tire course are being laid out, large metal tubes are laid horizontally and space is provided to allow these tubes to enter the room at the base. These tubes will run in this case 40 feet outwards to the north away from the house, and will act to draw in air from the outside. The air will cool passively in the earth as it is drawn into the house, also taking out any moisture along the way. These will be buried soon into the construction process. Grills to keep out pests and doors lined with insulation and a seal are placed at each end of the piping.
- Rebar is cut and bent into a squared upside-down U shape and pounded into the finished courses of tires. These are leveled using a leveled sight or surveying tool. These re-bar pieces will support the roof arches.
- Arched roofs are constructed by a separate team. Each roof structure is made of a re-bar skeleton and covered with a 6×6 inch re-mesh wire mesh, or cloth. This also has an layer on the bottom of metal lath. The re-bar is bent by hand to size and cut with a manual cutter. No machines necessary and no welding needed, either. These are all held together with bailing wire. Once finished a large group of people pick up these domes and walk them over to the building, carefully lowering them into place, adjusting them as needed. They are then attached to re-bar with more bailing wire, double tied.
- Behind the tire courses on the north side of the structure a small gap is dug, and behind this are placed two sheets of R-13 insulation with a poly sheet acting as a vapor barrier on their outside. The space between them and the tire walls are filled with earth.
- Rainwater catchment tanks are placed behind the insulation boards.
- Screws are set into the top course of tires to ‘porcupine’ the surface in preparation for cement.
- Cement is layered atop the tire courses narrowly, to support and accept aluminum beer or soda cans which have been squeezed in the center. They are set horizontally in layers. Concrete > cans > concrete > cans, etc, until the wall of bond beam created is 3 inches above the base of the arched roof’s base layer of horizontal re-bar.
- Temporary wooden frames are placed inside the roof domes to keep its shape for the oncoming processes that have great loads.
- Cement is laid atop the domes in thin layers.
- Trenches are dug at the front of the house and poured with concrete with vertical re-bar inserts. (Horizontal rebar laying across the trenches, too?). These will support the frames of the window panes and doors for each room.
- Simultaneously a solar (PV) system is being assembled. At this project, 12 x 230 watt panels are linked up with 4 sets of 3 panels in series. These feed two charge controllers, a bank of (HOW MANY WHAT TYPE OF) batteries, and a DC > AC inverter. The house’s lighting and refrigeration will be run off DC and any appliances that can’t accept this will be run of the inverter with AC. This allows for the inverter to be shut off for a lot of the time, which is quieter and more efficient.
- Another set of tire courses is laid a few feet in front of the house.
- A massive trench is dug between the frames at the front of the house and the tire courses.
- The site is covered each day with a massive tarp to keep off rain and other weather-related damage.
