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Hybrids In a sense, virtually all buildings are hybrids of one sort or another. Most modern buildings employ a wide range of materials, some "natural" some not. A strawbale house, for instance, is most likely a hybrid of strawbales and conventional wood framing. Unless the building is a dome or vault, the roof is likely framed with wood or steel. Our domed home is a hybrid of earthbag and papercrete materials. I know of a fine circular home that was minimally framed with 2X4 studs and then strawbales set on their ends provided the insulation. I am completely in favor of using hybrid building concepts, because it frees the mind to use whatever material or technique is appropriate for any given application or aesthetic. Cob is a wonderful material for creating curved, sensuous forms; adobe and rammed earth are great for thick, fairly straight walls that serve as thermal mass; earthbags can be used for either curved or straight walls that can be either insulation or thermal mass, depending on what they are filled with; strawbales are best used for straight, thick, insulating walls; cordwood construction provides both thermal mass and insulation, and is easiest when forming straight walls; old tires make great retaining walls, or even foundations for other materials; aluminum cans can be mortared into walls of any shape; papercrete is primarily an insulating material that can be used as a plaster, or a structural material and is extremely malleable; rocks provide wonderful thermal mass and can be stacked in a variety of shapes. I suggest that you take advantage of the materials that can be found nearby that do the job required and appeal to your fancy. If it weren't for building codes, the only rules for how you build would be the laws of physics and mother nature. So, go for it when you can!
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RESOURCES Earthbag/Papercrete/Steel Quonset Vault EXPERT ADVICE Cement
Cordwood Earthbags Foam Geodesics Papercrete Steel Stone Strawbale Tile Tires Mobile Homes Wood Miscellaneous
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Baca Hybrid Kelly Hart, Designer  This is a 2 bedroom, 2 story (3 levels), 1250 sf (to the outside) house that was designed as a hybrid, passive solar model to demonstrate the plan elements needed to submit for review in a covenanted community. It is a compact design that incorporates many aspects of sustainable architecture, including an attached solar greenhouse, a naturally cooled pantry, and the use of some natural, local materials (earthbags and strawbales). The appearance is fairly conventional, but it does have a curved north wall, for interest and strength of structure. It should be quite energy efficient, requiring little back-up heat (provided by a wood or gas stove). Even though the square footage is small, with the three levels there is much diversity and interest inherent in the design. The upper loft area would be accessible via a separate entrance on the north side. Clerestory windows facing south bring light to the upper level rooms, and provide excellent ventilation for the entire house. The house could be situated on a south-facing slope, or artificially bermed on the north, east and west sides.
For more information about this plan, and many others, visit our sister site www.dreamgreenhomes.com, where you will find a wide range of plans for sustainable homes, greenhouses, small buildings, garages, and food storage space for sale. Dream Green Homes is a consortium of outstanding architects and designers, who have pooled their talent and expertise for your benefit. |
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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.
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. 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.
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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Michael Shealy in conjunction with Leonard Jones, P.E., has been designing structures using tire bales. These are massive bales made by compressing about 100 tires into a 5' wide x 6' long x 2.5' high block and banding them with heavy duty (~3/16") stainless steel wire. Each bale weighs about 2000 lbs. They can be used as giant building blocks to put up walls or columns in a building. The footprint is very large and even though the weight is quite a bit more than a conventional house, a foundation is not needed... Just excavate the existing soil, level and compact it, and start stacking tire bales... The only restriction is that you ought not to start stacking these on organic or expansive soil. Once you have the bales stacked, you add a bond beam - more as a place to fasten your roof structure than as a means to hold the building together. Then you stucco/plaster the exterior or interior, either by hand or by gunniting. When the wall is stacked, there are some considerable voids between the bales which should be stuffed with insulating material before the building is stuccoed/platered... The bales are very strong. One bale was tested on a giant compression testing machine at the Colorado School of Mines (CSM). It resisted compression with very little deformation until one wire broke at a load of 600,000 + lbs and they concluded the test. The bales have not been tested for thermal conductivity or heat capacity, although a group of students at CSM attempted to model thermal conductivity based on the tire bale constituents. It will be interesting to see how a house built from tire bales works in "real life." The pictures were taken at the tire baling facility near Fountain, CO... just south of Colorado Springs. The folks on the bales are Mike Shealy and his grandson. The wall is 4 bales high (10 foot).
Mike Shealy wrote: "In 1998, I was contacted by the folks at Midway Tire Recycling, having found that I was doing (generic) rammed-earth tire-house designs, and asked if I would be interested in the tire bale as a building block for residences? I took a drive down to Fountain to see them and immediately WAS interested. The Houtchens, Vernie & Ann, wanted to build their own home on their property by the tire recycling facility. After some discussion, I suggested they create an engineering document for the tire bale, ie, test results, statements of practical & comparable bearing loads, coefficient of friction and insulation values, from actual tests. This document, I told them, could/would be used in all future building using T-bales as a *bearing* building material. They told me that the T-bale wasn't *suitable* as a unit in a load bearing wall and presented me with a study done by CSMines students that concluded the same, based purely on the fact that they continue to compress as pressure is increased. This study gave no attention to the actual loads that would be developed from framing a roof on them, hence it was not practical. They asked me who would create this document and I suggested Tom Griepentrog, the engineer who created the rammed-earth-tire-wall document for the Dennis Weaver home. Tom quoted a very thorough procedure, acceptable to me and probably future engineers. This document would make it easy for all future engineers to verify the stability of the T-bale as a berm/bearing wall for use in residences ...BUT... The Houtchens apparently had different ideas, didn't like the price for the document ($8,000), and they dumped me (& Tom) and elected to go to a non-engineered use of the T-bales, as purely *infill*, as in straw bales, using a steel post & beam structure instead. This was unacceptable to me, as it gave nothing to future uses. So, until 2002 when I 'met' Leonard on an alternative building mailing list, I just held the idea between my ears, but since meeting him have had four commissions to design T-bale homes." To see what Mike Shealy has been up to with the tire bale projects, you can visit: www.touchtheearthranch.com www.hagartirebales.com chronicles the building of a tirebale house in Colorado. frtirerecycle.com sells these huge bales of recycled tires. buildwithearth.com is a PDF file that addresses some engineering concerns about building with tire bales. |
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This is about our Roundhouse at Brithdir Mawr, near Newport in Pembrokeshire, Wales, UK. A self-built and designed ecohome of wood, cordwood and cob construction, partially earth sheltered and with a turf roof. This website describes the use of lightweight straw-clay sandwiched by ferrocement to form structural panels. hybridadobe.com Site with lots of pictures and description of a variety of hybrid papercrete/adobe/strawbale structures. groundwork.org Groundworks Institute's Nicaraguan Project details how they constructed a $300 house using local materials. greeninventor.org/strawjet describes an innovative way of creating load-bearing beams using long straw and papercrete. simondale.net/house A wonderful example of a hybrid home made from local, natural materials in the United Kingdom. hybridconics.com describes a light-weight, super-insulated steel/sheet metal/ polymer cement structure based on conics. youtube.com features the building of a Bamboo/Strawbale building. iflux.com.br/bienal/laminas.pdf shows a hybrid bamboo/earthbag structure built in Brazil. redearthjourney.blogspot.com shows how abarn-style hybrid earthbag/strawbale/recycled wood home was built.
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This cross section shows the hybrid nature of this design. The primary exterior walls of the lower story are made with earthbags filled with insulating material. These walls on the second story, above grade, are strawbale. The rest of the structure is more common stick-frame construction. The foundation is a poured monolithic slab over insulation, providing much of the necessary thermal mass for good passive solar performance. 
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 (see 
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.
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.
This picture clearly illustrates that there is no shortage of this resource. The distant black-colored areas are thousands of tire bales. The area in the foreground contains a tire-baling press and tens of thousands of loose tires. 
