AWCP PERMACULTURE PROJECTSuperadobe Root CellarLeandro “Nachie” Braga – 4/28/10

“Earth turns to gold in the hands of the wise” - Rumi

OVERVIEW AND PERSONAL PHILOSOPHY:

The subject of this report will be the construction of a root cellar on the Alderleafcampus, utilizing the north-facing earth cavity and drainage system already in place fromearlier plans and taking advantage of this niche as a exciting opportunity to bring NaderKhalili’s visionary “superadobe” earthbag construction techniques to the property. Due tothe relative simplicity of design required by a root cellar as well as its limited size, this infact offers Alderleaf the best possible opportunity to learn the methods of superadobedome construction in a manner that presents the fewest possible difficulties in technicaldesign while enabling us to build confidence and experience towards future endeavors.

For the purposes of this report it would seem useful to indulge in a shortdiscussion on the appropriateness of superadobe to permaculture design. Because thesuperadobe dome (and in particular those constructed of mixed cement-stabilized earth)functions essentially as a man-made cave, it lends itself perfectly to the idea ofunderground cold storage. However there are perhaps more important, ideological aspectsto consider when choosing to bring superadobe into a permaculture design.

At its heart, permaculture seeks to emulate natural systems and structure in anattempt to re-envision humanity’s relationship with “Gaia” - an amazingly complexsentient organism composed of all life on this planet, with an interconnected awarenessstretching beyond the dimensions of reality that even the most advanced modern quantumphysics are yet capable of shedding light on. This paradigm must always remain at theforefront of all our design efforts; an intense humility in the face of nature’s mastery

forefront of all our design efforts; an intense humility in the face of nature’s masteryshould inform our every action, and in particular should prevent us from ever trying toovercomplicate things. Though modern society is capable of building everything fromskyscrapers to steel roofing that will not need to be replaced for generations, none ofthese things are “permanent” in the sense of coexisting with nature’s effortless dance.None of them will survive the test of time, and more importantly none of them providefor us a sense of truly belonging to the land we are interacting with. The more we seek toseclude our living spaces from the earth which sustains us, the further we stray from whatit is to be truly human.

Superadobe is a living sacred geometry that we may lay claim to with our barehands. The spiraling dome and hexagonal principles of weight distribution recall the mostsuccessful fractal patterns of nature. The completely un-mechanized aspects of itsconstruction invite all layers of the community, without the artificial divisions of laborimposed by civilization and specialized work, to come and recreate the world in theirown image. It learns a design lesson from the sea creatures that only follow their owngenetic instincts to make their shells, the most beautiful homes, with the best forms, fromthe seawater itself. In the words of superadobe mastermind Nader Khalili, “If a little seacreature, who does not claim as we do to be created in the image of God, can make ahome which is the best shell structure, best patterns, colors and texture, a home which isin harmony with the ocean environment and which is all created from sea water andwaterproofed with water, then why shouldn’t we be able to pick up the earth and build ahome for ourselves that can resist the elements and works in harmony with nature?” SUPERADOBE: “I was searching for a way to create a building that was totally in harmony with nature,that could be available to everybody around the world.” – Nader Khalili, interview withAIA (American Institute of Architects)

Superadobe (also called Super Adobe) is a form of earthbag construction that wasdeveloped by Iranian architect Nader Khalili. The technique uses layered long fabrictubes or bags filled with adobe (“super” long tubes of adobe = superadobe) to form acompression structure. The resulting beehive shaped shelters employ arches, domes, andvaults to create single and double-curved shells that are strong and aesthetically pleasing.Khalili originally developed the superadobe system in 1984 in response to NASA’s callfor housing designs for future human settlements on the Moon and on Mars. His proposalwas to use moon dust to fill the plastic superadobe tubes and Velcro together the layers(instead of using barbed wire).

In response to refugees from the Persian Gulf War, in 1995 15 refugee shelterswere built in Iran by Nader Khalili with the United Nations Development Programme(UNDP) and the United Nations High Commissioner for Refugees (UNHCR). Accordingto Khalili, that particular cluster of 15 domes could have been repeated into thethousands, but the government dismantled the camp a few years later. Since then, thesuperadobe method has been put to use in Canada, Mexico, Brazil, Belize, Costa Rica,Chile, Iran, India, Siberia, Mali, and Thailand, as well as in the U.S.

Many different materials can be used to construct superadobe. Ideally one wouldhave barbed wire, earth or sand, cement or lime, and superadobe fabric tubing (availablefrom Cal-Earth), but the bags can be polypropylene, burlap, or some other material. Whatis important is that they are UV resistant, or else quickly covered in plaster. In this regardyou can even use grocery bags that are twisted shut and formed into balls. Virtually anyfill material will work including un-stabilized sand, earth, gravel, crushed volcanic rock,rice hulls, etc. If the fill material is weak the bags have to be extremely strong and UVresistant, or else plastered right away. The material can be either wet or dry, but thestructure is more stable when the tube's contents have been moistened. Other materialsneeded include water, shovels, tampers, scissors, large plugs or pipes (for windows), and

needed include water, shovels, tampers, scissors, large plugs or pipes (for windows), andsmall buckets or coffee cans for filling the sacks.

The foundation for the structure is formed by digging a circular trench 12” deepwith a diameter of 8’-14’. Two or three layers of the filled polypropylene sand tubes(superadobe fabric tubing) are set below the ground level in the foundation trench. A ropeis anchored to the ground in the center of the circle and used like a compass to trace theshape of the base. Another rope is fastened to the ground on the inside base of the walland used as a guide to shape the interior radius of the opposite wall of the dome. Ropescan be used from several points around the inside of the base to ensure accuracy of thefinished dome. Other “compass” systems exist utilizing a free-swiveling metal pipe, butfor the purposes of this plan we will assume ropes or chain.

On top of each layer of tamped, filled tubes, a loop of barbed wire is placed tohelp stabilize the location of each consecutive layer. Doors and windows can be cut out ofthe interior of the dome before the stabilized earth sets, or built around wooden forms.PVC pipes can be sandwiched between different layers to create vents and small windowswith very little difficulty. Once the corbelled dome is complete, it can be covered inseveral different kinds of exterior treatments, usually plaster. Khalili developed a systemthat used 85% earth and 15% cement plaster and which “reptile”, a veneer of grapefruitsized balls of concrete and earth, then covers. Reptile is easy to install and because theballs create easy paths for stress, it doesn't crack with time. There are many differentpossibilities, some more appropriate than others given climate and available buildingmaterials.

Superadobe has also proven to be competitively strong by modern Westernconstruction standards. Strength and resiliency tests done at Cal-Earth under thesupervision of the ICBO (International Conference of Building Officials) showed thatunder static load testing conditions simulating seismic, wind, and snow loads, thesuperadobe system exceeded by 200 percent the 1991 Uniform Building CodeRequirements, actually causing the high-tension machines used for the testing tothemselves fail.

Due to their impressive structural stability, relative ease of construction anddeeply insulated walls, superadobe presents itself as a perfect method by which to createa root cellar. ROOT CELLARS:

Root cellars are at once one of the simplest and most practical aspects oftraditional and modern “off the grid” living. Constructed from a variety of materials,

traditional and modern “off the grid” living. Constructed from a variety of materials,either integrated into basements or as outbuildings as in this case, they provide aninvaluable means of storing food year round when more conventional means ofrefrigeration may not be available. Particularly as suited to the needs of a farm wheremass quantities of food are likely to be harvested in periodic spurts and need to beimmediately stored – as opposed to in modern households where a small refrigerator will(at a high cost in energy) preserve a limited amount of food until it’s time to go to thegrocery again – a root cellar makes it possible to enjoy fresh fruits and vegetables wellinto the winter months and indeed opens up avenues of sustainability and self-dependence that would otherwise be unimaginable.

Cold cellars, as they are also known, are simply subterranean storage rooms -often quite small - that use no power and rely upon the natural temperature and humidityof the earth to preserve the harvest they contain. Ideally they have earthen floors to helpkeep the humidity high: an aspect we will be incorporating into this design. A 4-inch ventprotrudes from the earth and sod-covered roof, dropping to just above the cellar floor andallowing cold air in from outside. A “damper” can be constructed of wood or othermaterials to block the vent and help regulate airflow. The door is insulated (often withcommercially available fiberglass material) and can even be doubled up into an airlock, inwhich case a second vent can be added just under the ceiling to give warm air a place toescape. In most scenarios the door would be found at the bottom of a short flight of stairs,the top of which is also covered. These particular variations in design will be left up tothe property managers, and are covered below.

While superadobe structures are readily adaptable to the needs of modernplumbing and electrical wiring, for this design we will forego any such accoutrements -keeping in mind our goal of simplicity and the need to move away from reliance of anykind on the central power grid. Any number of solutions exist to the challenge ofproviding adequate light in the cellar: my suggestion would be to paint the interior wallswhite and keep a space inside for candles or a lantern. Given the small amount ofavailable space, sunlight from the doorway when entered in daytime may be sufficient toilluminate the shelves if a two-door airlock is not used.

Again, though superadobe can easily have shelves, stairs, and other complexelements implemented into its structural design, the specific needs of a root cellarpreclude this. All shelving systems should be spaced at least one inch from the wall so asto provide continual airflow. And while the rounded shape of the superadobe dome wouldseem to provide quite an obstacle to convenient storage space, it is only a simple matterof constructing rounded shelves from OSB board, with cinderblocks or other spacers inbetween, building them up. The lower shelves could be made deeper to accommodate thesloping wall face, and thus will serve as storage for large items such as bins of rootvegetables. Where possible I will try to highlight these various eccentricities in design inthe following pages on practical construction. I have avoided attempting to determine theexact proportions and organization of interior storage units, as these will need to beadapted to the final dimensions of the structure as well as the specific needs of what is tobe stored. An advantage to not making the shelves integral to the structure itself is thatthey may be rearranged or completely overhauled as necessity dictates. PRACTICAL ASPECTS OF CONSTRUCTION:

In this section we will deal with the step-by-step construction of a superadobestructure that will fulfill the basic needs of a root cellar for the farm. I would like to stressthat although some effort has been made to provide an accessible overview of theconstruction and design process, as well as to highlight the specific areas of interest andchallenges inherent in this particular project, this text cannot stand alone as a guidewithout either a detailed design manual such as the one referenced in Appendix III, or theinvolvement of an experienced earthbag builder. For an accurate assessment of materials

involvement of an experienced earthbag builder. For an accurate assessment of materialsthat will be required as well as a generalized cost analysis for similar projects, seeAppendix II. It is important to note that while this project may be undertaken quitesimilarly using traditional “small” sandbags, I would highly recommend investing inseveral rolls of the Cal-Earth Institute’s (www.calearth.org) long bags for this and futureprojects. In fact I believe it would be folly to proceed without these important tools,seeing as how they are currently available and quite affordable, and would cut downsignificantly on the necessary labor. In addition natural fiber bags, such as burlap or jutefabric are normally sprayed with toxic chemical preservatives (formaldehyde) and areprone to mold and insects. Other than the bags, cement, pipes for venting, optionalwaterproofing material and the 4-point barbed wire, the only required tool that is notcurrently present on the farm is a plumber’s tamp, and even that can be easilymanufactured with cement and a suitable handle – though of course I would recommendpurchasing a higher quality commercial tamper.

By far the biggest obstacle to this project, as with most construction on thisproperty, will be the overabundance of water on site. This may make it relatively difficultto lay a sturdy foundation, and further research may be needed to find other possibilities(such as an added moisture barrier around the foundation bags) should the methodsoutlined below seem insufficient. As always however, one must proceed with a strongfaith in the technical superiority of the superadobe system and its ability to amaze eventhe most skeptical observer with its versatile nature and longevity. The amount ofresearch done on underground superadobe is not extensive, but seems to indicate that theburmed earth provides a formidable safeguard to water damage, particularly when addedto the traditional exterior coatings. In fact, it is only the weight of the earth itself over thedome that seems to pose any theoretical difficulties, though even that can be easilyovercome through use of the stabilized earth method, perhaps with cement at a greaterratio than 10-15%. If desired the structure could be further waterproofed by adding eavesof metal or wood at a downward slope off the dome once it has cleared the top of itsfoundation. These would then be covered with any effective sheeting or shingles todeflect water away from the dome itself. However given that the structure will be coveredin earth and there is already an effective French drain system built into the foundation, Ido not feel this to be necessary.

Once again I would like to underscore how fortunate it is for us to be able tointroduce this amazing architectural system to the property via a relatively “bare bones”structure such as the root cellar. The extreme simplicity called for by this design shouldenable the entire core structure to be built in a week or less by a crew of 3-4 people,allowing of course for unforeseen circumstances. Getting Started – Soil Tests

A couple simple field tests need to be undertaken with the soil on site to determinehow suitable it will be for this type of construction. We will presume to use as much ofthe earth that has already been exhumed from the site as possible. Much as wasdemonstrated in earlier permaculture classes with the “jar test”, samples of this soilshould be put in jars, which are then filled with water and shaken and then left to settleout for several days. This will determine the ratio of clay (top layer) to sand and silt(middle layer) and pebbles and coarse sand (bottom of the jar). For sandy soils, cement orlime will work as the best stabilizing agents. For adobe/clay soils, lime or asphaltemulsion is preferable. Mixing the Stabilized Earth

Next we will need to determine the optimal ratio of earth to stabilizer. This of

Next we will need to determine the optimal ratio of earth to stabilizer. This ofcourse can vary greatly, though traditionally a 10:1 ratio is used. As indicated above,additional stabilizer may be added if budget and necessity dictates. We begin this test bymixing the earth and stabilizing agent together and wetting it to a moist, muddyconsistency. This mixture is then packed firmly into three plastic cups and left to dry inthe shade. After several days, the cups are removed and the hardened samples aresubmerged in a bucket of water. If the samples have not eroded after three days, then themix is suitable for filling the bags and creating the stabilized superadobe structure.Obviously, the percentage of stabilizer should be reduced or increased to achieve the bestpossible mixture.

When mixing the stabilized earth in large quantities, you will want to remove anylarge rocks, but keep the gravel. All organic material must also be removed. The cementor lime must be consistently mixed with the earth and water. Cement is preferably mixedwith the earth before water is added, while lime must be mixed with water before beingadded to the earth. The mixing may be done by hand or machine. The final mix should beevenly moist, but not wet, to ensure maximum density of earth particles. When yousqueeze the mix in your hand it must form a ball that does not fall apart, yet does not dripwater. If too dry, the earth will fall apart when compacted, and will not harden inside thebags. If it is too wet it will become fluid when tamped, making it difficult to build withand weaker when hardened. Several balls of the stabilized earth should be tested in thismanner to ensure that it is suitable for building. Laying the Foundation

Traditionally, a foundation ring must be dug, leveled, and laid before the domeitself can begin to take shape. For this project however, it will be sufficient to make surethat the dome is sitting on level ground in the pre-dug root cellar pit. This can be done byfirst removing all organic material and excess earth from the foundation, tamping it tolevel, and then filling it up a foot or more with the available gravel. This gravel will serveas a floor for the interior of the root cellar, allowing humidity to come up from the earthbut also ensuring that all water runoff from outside the dome flows smoothly into thedrain. Much like with the chicken coop project, it will also provide us with an easy levelsurface over which to build the structure.

We then determine where the center of the dome will be in relation to itsmaximum diameter as allowed by the existing foundation, and mark out an even circlefor the exterior diameter of the dome. I would suggest that this be done with spray-paint,since it will be difficult to mark the gravel in any other manner. The measurement ismade by driving a stake into the center of the pit and extending a rope horizontally offfrom it that can be swiveled around the center stake to show an equal distance in alldirections. This will be our center compass. An inner circle is then marked, usually 12”(depending on bag width) from the outer one. These lines demarcate where the first fewfoundational rings of the superadobe dome will be laid. Though from this point afoundation is usually dug 10” down and leveled, for this project we should be able to laythe foundational rings at ground level to preserve water drainage.

Trenches must also be dug for the entry buttress walls, though technically sincethe entry is so much higher than the bottom of the root cellar itself, they could be made toextend from the doorway only at ground level, trusting the mounded earth itself to serveas enough for a buttress for the foundation. Since we’ll be building up several layersbefore even getting to the entry level, this dome will also have a much strongerfoundation than is technically required. Care should be taken to make sure that the initialfoundation rings do not cut off the French drain, though with enough of a gravel bed thisshould not be a problem. Foundational Rings

Foundational Rings

The foundation is made up of at least two complete rings of sandbag coils with alayer of barbed wire in between. This is why the foundation is usually dug to 10” belowground level, though that is not a concern here. These complete rings stabilize thefoundation of the dome, particularly against horizontal forces such as earthquake andflood. The method described below for filling the foundational bags is to be repeated forall subsequent layers.

A length of sandbag tubing is cut from the roll using scissors (a knife may shredthe bag) and one end pinned closed or even just folded under itself and held closed by theweight of stabilized earth as it is added. There are several methods for filling thesuperadobe bags, with one of the most popular involving a chain of people passing theearth down the bag or simply passing cans of earth from the point at which it is mixed tothe point at which it is put in the bag. The bag can also be turned inside out andscrunched up against itself in order to bring the opening closer to the point where theearth is being packed down. At first, the bag is filled vertically like a short column so thatgravity helps fill the start of the bag very full. This is important due to the tendency ofbags to get too thin at the end of a row. The builder then continues to fill the bag withgravity’s assistance, sloped up against her/his leg or other prop, while walking backwardsalong the circle.

While the bag is being filled and placed by the builder, it is constantly checkedwith the center compass to make sure that it is creating a perfect circle. At this stage, theinside edge of the bag will be about half an inch or one finger width beyond the compassline (this is because the bag will be flattened out during tamping). Tamping, orcompacting, is accomplished with a plumber’s tamper once the bag is completely full.This will cause the bag to widen out and flatten. Before tamping, make sure that the bagis still within the compass curve. Tamping should be done by dropping the tamper on thebag and loosening one’s grip as it hits, using the weight of the tool itself to do the workand minimizing arm and back strain. A brick may be used to compact smaller detailareas, for the sides of bags, or for the whole dome if necessary. To check if your bag issufficiently compacted, press your finger to the outer edge. If it dimples, tamp somemore. The outer edge should be a smooth curve and feel firm. When the earth mixture isnot tamped enough the sides and ends of the bags will crumble and are weak. Stabilizedearth in particular will not stick together properly if it is not well tamped, since it is dampbut not wet like concrete.

After one row is completed, barbed wire must be laid across it to act as the“rebar”. Barbed wire is tensile reinforcement for the dome and resists the tension createdby the shape of the dome as well as live loads and seismic forces. There must not be anybreak in the continuity of the wire: where strands end they must overlap by 2 feet and betwisted together. The barbed wire must be four-point, two strand, and galvanized. If thereare only 2 points on each barb it will not grip well enough, and the double strand willtake up tension in the superadobe wall to resist diagonal cracks forming. The barbed wireis placed in the center of the bag, not less than 3 inches from the edge. To attach it yousimply push the barbs down into the bag, and use bricks or other weights to hold it inplace while waiting for the next row. In order to “overbuild” the structure and make itmore likely to withstand the pressure of piled earth, the barbed wire may be doubled upin a figure-8 pattern between each row, which will add extra tensile reinforcement.Remember to keep the wire as continuous as possible, particularly in any areas where theends of two bags are meeting.

The second foundation row of the dome is also one completed ring of superadobecoil, laid over the barbed wire. Thus a continuous tension ring will run under the doorwaysill. Always remember to check the compass circle as you are laying the bags, and thinkahead by taking into account how the bags flatten when tamped. There must be a row ofbarbed wire between every row of superadobe. The design must also prevent the barbed

barbed wire between every row of superadobe. The design must also prevent the barbedwire from getting wet. Additionally, when it is sandwiched between inert plastic bags thegalvanized steel is less prone to oxidation. Building the Base Walls

Once enough vertical foundational rings have been build up to ground level wherethe door entry will be, a couple more base rows will be added, together with thefoundation making a low cylinder that is kept circular by the compass. Since the baserows sit directly on top of the foundation, they can be kept vertical using a carpenter’slevel. It may also be preferable to not build the foundational rings all the way up to theground surface, so that a step down into the root cellar may be created. After the lastfoundation row a space must be left for the door opening in the base rings. For thefoundations or walls, not all layers need to be level horizontally and may undulate thickeror thinner depending on the skill of the builder. To keep an overall level for the wholebuilding, the thickness of each layer may be adjusted row by row.

As more walls are added, it is important to fill the bags on the wall itself or else

they will be too heavy to lift into place. The fuller the bag is made, the less work overallsince you will need fewer rows to complete the dome. Two separate builders can also fillone long bag from both open ends at the same time, potentially completing each row inhalf the time. Creating a Doorway and Beginning the Buttress Walls

Though a small doorway can be made in the dome without the use of buttresswalls, for the root cellar we will assume that we are hoping to use a traditional door thatan adult can walk through without having to hunch. When such a large opening is madein a dome, buttress walls are needed on either side. These walls are perpendicular to thedome and will also create a protected entryway with a door vault over the opening toprotect from rain. The buttress walls should be built at the same time as the dome so thatthe barbed wires and bags can connect together. Buttress walls are usually two to threefeet long, and tied into the dome with barbed wire at each layer. If not using the figure-8method, the barbed wire must be looped back at the end of each wall so as to create extrastrength. Obviously, it should also overlap from the bags creating the buttress walls ontothe bags forming the base walls.

We will want to set in a frame (probably of wood) as a guide for the door openingas the dome walls go up. The door should not be much more than 2ft wide by 6ft tall. Theframe can be tied into the dome walls using barbed wire loops, and should be leveled

frame can be tied into the dome walls using barbed wire loops, and should be leveledhorizontally and vertically. Building the walls on either side of this frame will continueexactly as with the foundational rings, though of course the coils will now stop on eitherside of the frame. As more bags are placed and tamped up against the frame it will befirmly held in place. However, it should be temporarily braced open if the material isflimsy. An insulated door of the correct dimensions should be acquired before the frameis built and put into place, so that it will be sure to accommodate installation upon thedome’s completion.

Once a couple base walls are built up around the door frame, you are ready tostart the dome itself, which will gradually curve inwards to close at the top. The levelwhere the base ends and the dome begins is called the spring line. At this level the domeneeds a second compass to create the correct curve. This is called the “height compass”. Establishing the Height Compass

The height compass is positioned in the doorway on the outside of the foundation,

and like the center compass is made from a rope or chain. Its main function is to tell ushow much longer we need to make the center compass in order to correctly measure thepositioning of higher rows. Thus the height compass controls the shape of the LancetArch. For practical reasons, we fix it on the outside of the door frame and draw the ropeout to the opposite inside face of the dome. Unlike the center compass, the heightcompass always stays at the same length. Because the height of the finished dome isapproximately equal to its diameter, we are able to draw the height compass at itsestablished length up from the fixed point outside the doorway and determine the exactinward slope of the dome walls as they get higher.

As we begin constructing any row of superadobe above the vertical base rows, webring the two chains/ropes (height compass and center compass) together and adjust thecenter compass length by matching it with the height compass. Therefore, at every rowthe center compass increases in length to match the height compass. Once the centercompass length is set, the height compass is no longer needed for that row.

A much more detailed step-by-step guide to the different uses of the compass andhow to accurately calculate the various angles necessary for different superadobeapplications can be found in Appendix IV of Nader Khalili’s book Emergency SandbagShelter. Building the Dome and Buttress Walls

Once you have gotten the basics of the compass down, building up the domebecomes a repetitive process of adding progressively smaller superadobe and barbed wire

becomes a repetitive process of adding progressively smaller superadobe and barbed wirerings over the last row, gradually “corbelling” inwards to create the dome shape. At thisstage in the process, the compass will do most of the work in helping you keep the tubesat the appropriate position. Because the root cellar will only have one or two small ventsand no windows, for this process we will dispense with many of the more complextechniques in superadobe such as putting windows or larger arched openings in the sidesof the dome. This is one of the major reasons why this root cellar provides us with such afantastic beginner’s project. We will, however, have to put in buttress walls for the largedoor opening.

As mentioned above, the buttress walls are generally 2-3 feet long, but cancertainly be longer if one wishes to extend them into a type of airlock, which will bediscussed below (personally I do not feel that this is necessary given the extremeinsulation of the superadobe and the extra work required). The walls begin at the level ofthe foundation, or in this case at ground level. I might suggest digging a separatefoundation for the buttress walls so that they can be tied into the dome wall at an earlierstage, but only if this can be done without disrupting the existing drain system.

The buttress walls should be about one row higher than the door frame itself, andabout 3 feet apart for a doorway 2 feet wide. The door buttress bags connect to the domewith barbed wire and by overlapping into the dome wall with every other row (think ofinterlocking “teeth” like a zipper) During construction the buttress walls can be steppedback and used as a staircase to climb up and down.

If the door frame needs to be mechanically attached to the walls, barbed wire canbe nailed to the frame and sandwiched between the bags. The frame must fit snugly intothe dome walls, but if needed extra bags can be laid in vertically and filled from above toclose any gaps. Because the frame needs to be mechanically attached to the dome walls,barbed wire must be nailed to it and sandwiched between the bags. This will allow for aconventional door to be attached, later. For a flat lintel over the doorway as proposedhere, extra barbed wires should be tied into the outside of the dome/buttress walls fromseveral rows lower than the lintel, to support it. These wires must be at least six feet long,and will support the lintel from below. The last two rows of the buttress walls should tiedirectly into the dome wall. Covering the Door Frame

As mentioned, several strands of barbed wire must be laid across the door openingand connected into the dome several rows below the layer at which a superadobe bag is tocross over the door frame. Superadobe can be made into an un-reinforced lintel over arectangular door of no more than 2 feet when filled with stabilized earth (as is the case)and supported from below by several barbed wire strands or materials such as a plank ofwood, steel pipes or rebar. These materials can be later removed or left in place as part ofthe structure.

The main challenge is to lay the first row over the door lintel, as it needs the mostsupport (particularly during tamping). Once that first row is laid, the rows above itactually act as reinforcement by helping to carry the lintel row via the barbed wireelement - thus, it becomes an integral part of the overall dome. In effect, each succeedingrow makes a thicker and thicker beam element. The rows above the door are tied togetherwith two strands of barbed wire (if only one was being used from the beginning) toprovide extra resistance to tension. As always, the wire should be well sandwichedbetween the rows of bags before tamping. Finishing the Dome

The upper rows of the dome are the trickiest to put into place, because thecompass will call for ever-increasing inward steps. When walking on the dome during

compass will call for ever-increasing inward steps. When walking on the dome duringthis stage, always make sure to step on the outside edge of the bags and try to stand acouple of rows down from the top. It may help to leave the very upper rows to be built ona separate day, so that the lower ones will have had time to cure and harden by the timeyou need to be putting your weight on them. At first, the bag should be placed directlyover the lower row. As the coil is filled and twisted, it will work its way inward towardsthe compass line. The bag should begin to be shaped with a brick right away, three orfour feet after it is filled, to stop it from slipping too far while the rest of it is coiled. Youshould keep measuring with the compass, and if needed fill the bags with less earth tomake them flatter and wider. It is easy to tamp the bag inwards, but harder to push itoutwards.

The finished bags should match exactly the compass line. If this is not the case, itis better to remove an entire row and start over than to leave an unsafe base for the nextrows above. The outer part of the coil should be tamped first, as this is the only part withsupporting rows underneath. Tamping should be done to give the bags a gentle slopetowards the outside, which will help shed water and allow the next row to step in more. Abrick can be used to tamp the bags from below if a smoother look is desired on the insideof the dome. Barbed wire should be placed on the inside edge of the bag and made sure tobe gripping both above and below. At this stage in the dome, windows are generallyunsafe to add, but small vents may still be put in (see next section).

When the curve gets really tight towards the final rows, the bag should be filledand shaped simultaneously, using a brick. This will help to keep the bag from movingaround and keeps it firmly on the curve until the whole row is tamped - one or twopersons can accomplish this. Experienced builders are able to put the last rows togetherusing a single spiral bag rather than individual circles. Just make sure to keep overlappingand twisting the barbed wire together when more needs to be added. At the top of thedome, the coils step in as much as 3 to 5 inches, and the curve is so tight that each coiledring is partly self-supporting. A small bag may be placed at the very top to close off anyremaining sunlight. Considering the Vents

Pipes are extremely easy to add into superadobe walls: one need only lay a sectionthat will protrude from either side of the wall over a given row, and then lay the next rowover it as usual. It is preferable to fill the upper tube on either side of the pipe and leave itflat over the vent. Barbed wire must continue both above and below the pipe. Since theseare vents, they should actually slope inward rather than outward, as would usually bedone so as to keep out water. The rows of superadobe will be level again a few rows aftereach pipe.

Where exactly the vents are to be added will depend on the final design. Therequirements for root cellar vents were covered earlier in this text. I would suggestmaking them entirely of 4” PVC pipe, held together with conventional plumber’schemical glue. Only the cold air sink is technically necessary, and this can be made byattaching an angled elbow to the inside of the pipe to run it towards the floor. Anotherelbow joint can be attached to the outside to extend the pipe out above the dome so that itprotrudes from the eventual earth mound covering. At the end of this pipe a T-joint couldbe fitted with elbow pieces facing downward on either side, which would then be sealedup with wire mesh and ¼” hardware cloth to prevent any little critters from getting in. Asecond ventilation shaft is only really necessary if the door is made airtight. The Door Entry Vault

A small vault added over the buttress walls will protect the door opening fromwind and rain. A leaning arch technique can be used to cover over the buttress walls

wind and rain. A leaning arch technique can be used to cover over the buttress wallswithout having to use a form. To build a leaning arch, first two short bags are set on thebuttress walls and pitched against the dome. Then two longer bags are shaped over thesmall ones. Progressively longer bags are added until the two sides meet and form anarch. Repeating the leaning arch makes the vault longer or shorter as needed. While thebags for the arch are being filled with earth, they must be continuously shaped andtamped with a brick, so that they maintain the ach shape for both side to meet in thecenter. The barbed wires connect the upper layers of the buttress walls and the leaningarch bag, and are placed between each leaning row.

Each element of the entryway is somewhat flexible in relation to the otherelements. For example, depending on the dome size, the door and frame can be set intothe dome wall or set in the buttress wall and vault. The opening in the dome can have asmall flat lintel or be arched. However, the overall relationship of elements must beconsistent with the dome size and material strength.

Since we’ll be using stabilized earth, a series of short lintels could be quicklyadded to make a “mineshaft” style entrance, spanning across the buttress walls. Thiswould be necessary in the event that one wanted to make an airlock entrance into the rootcellar with an outer and inner door. The leaning arches, however, are more weatherresistant and aesthetically pleasing. Waterproofing and Finish

As a general rule, waterproofing layers must follow available local waterproofingmethods that have proven themselves over time. To be effective, the waterproofing mustbe easy to repair or patch, adhere well to what is below it, be long lasting, and be flexiblefor expansion and contraction with the building.

Asphalt seems to be the best all-around waterproofing material for a project such

as this, especially given the extremely wet climate in which we find ourselves. First ascratch coat of exterior plaster is applied to the dome, filling in the coiled shape of thedome to give a good “plaster key” and actually taking advantage of its geometry to makeits own structure. Two coats of liquid asphalt are then trowelled or brushed (coldapplication) or hot-mopped over this scratch coat, generally focusing on the uppersurfaces and gutter areas. The first coat is usually more fluid and soaks into the plaster,bonding well with it, while the second coat is thicker. Next, fabric strips are pressed intothe asphalt to make a reinforced layer. The strips will overlap to cover the entire roofarea, and can be made from cutting open the bag material itself. This layer will resist thedownward creep of the asphalt over time, and prevent cracking from settlement. Thefabric layer is then covered with a third, thick coat of asphalt, which is sprinkled with

fabric layer is then covered with a third, thick coat of asphalt, which is sprinkled withsand to create texture for the finish plaster. The finish plaster may be done with the“reptile” technique described earlier, or simply as a smooth coat of stabilized earth. Inclimates such as ours water must not be allowed to collect on the surface of the dome toavoid freeze/thaw damage. Reptile may be more effective at combating this. Porous,breathable surfaces such as lime-sand plaster are traditionally used to resist frost betterthan denser ones, since the denser materials will hold water for longer periods of time.

A variety of industrial liquid sealants can be used instead of asphalt, depending onbudget and willingness to use more energy-inefficient chemicals. These could be applieddirectly over the first plaster layer. It is of course also possible to make waterproofingfrom clay and straw, but this would not be ideal for this application. The interior of thedome can be plastered smooth in much the same manner, or even just left as exposedbags. The bag material will start to decompose after 300 hours of sunlight, but this ofcourse won’t be a problem on the inside of the root cellar.

A final thought should be given to whether or not to try and cover the dome withearth. It should be able to resist moisture either way, though with an earth covering it maynot need as extensive a waterproofing layer. Old carpet can be laid over the dome to helpthe earth stick while fast-growing and beneficial plants such as mint can be planted aboveit, or sod can simply be laid down. It is of course a given that at least some part of theentryway will remain exposed to the elements. ADDITIONAL CONSIDERATIONS:

One of the trickiest aspects of successfully using a root cellar is the specific cropstorage requirements of different fruits and vegetables. A thorough investigation of theseobstacles should be made before implementing any particular storage design. One majorfactor affecting storage longevity is Ethylene gas, a naturally occurring compound inplants. It acts to increase respiration and hasten aging and decomposition of food. Whileproviding adequate ventilation to the root cellar should be sufficient to keep the buildupof Ethylene to a minimum, there is a concern in the case of attempting to store fruits andvegetables together. Although temperature and moisture requirements may be similaracross various species, fruits such as apples and pears emit Ethylene gas as they ripen,which decreases the storage life of vegetables. This may be especially evident inpotatoes.

For those reasons I would suggest that given the limited available space in theroot cellar, its final design focus specifically on the storage of either fruits or vegetables,though both may be kept if sufficiently separated. As with all infrastructure projects,some degree of physical experience via a testing period will be necessary to achieve thecorrect balance. Although root vegetables as a rule are most easily stored, the massivequantities of fruit already available via the Food Forest, cherry trees, and wild berriesmake it imperative to find room for those, first. If sufficient efforts are made to can thefruit produced by the farm for long-term storage, then this may not become an issue, asthe Ethylene gas should not affect the sealed preserves. This design may of course beadapted in the future to the changing nature of the farm’s overall production. Below Ihave provided a brief overview of the storage requirements for a typical sampling ofperishable foods: Apples and pears – These fruits require a cool, moist environment with the temperature atabout 35-40 degrees and about 80-90% humidity. Remember not to store directly next tovegetables. Beets, parsnips, rutabagas, turnips – These root crops need a cool, moist environment.Keep the temperature above freezing to about 40 degrees. The humidity needs to be atabout 90-95%.

about 90-95%. Cabbage – Cabbages store well at 32-40 degrees with a relative humidity of about 90%. Carrots – Another great cellar vegetable. High humidity (90-95%) and temperaturebetween freezing and 40 degrees. Onions – Need a very cool temperature (35 degrees) and a slightly lower humidity level(about 65%). Will do well hung from the ceiling, so incorporate hooks into the design ifplanning for them (these can be wedged between rows of sandbags at the appropriateheights). Potatoes – Another crop that sores well in a cellar, but must be kept away from fruits. 38-40 degrees is ideal, with a humidity of 80-90%. Storage in an outdoor potato moundshould be considered however, as it will not take up valuable space in the cellar. Sweet potatoes – Need warmer conditions for long storage, must be kept above 50degrees in high humidity, 80-90%

If, in the final analysis, superadobe seems an impractical method for Alderleaf’sroot cellar, I would suggest procuring a pre-poured concrete septic tank, which usuallycomes in two pieces and could be purchased and delivered to the site for a cost roughlycomparable to the construction of a dome. The septic tank form would make a veryeffective root cellar with few modifications, assuming a form can be found which fits thehole that has already been dug. The downside, of course, is that this option would beabout 3 billion times less awesome. APPENDIX I – SUPERADOBE GUIDE FOR ON SITE REFERENCE:

APPENDIX I - CONTINUED

APPENDIX I – CONTINUED

APPENDIX II – UNITED NATIONS COST ANALYSIS:

APPENDIX III – RESOURCES USED:

APPENDIX III – RESOURCES USED: Root Cellars by Charles Sanders; Issue #121 of Backwoods Home Magazine, pg. 62 Emergency Sandbag Shelter by Nader Khalili, Cal-Earth Press 2008 ***** Cermaic Houses and Earth Architecture by Nader Khalili, Cal-Earth Press 2008 Earthbag Building by Kaki Hunter and Donald Kiffmeyer, New Society Publishers 2004 Additional Resources: Root Cellaring: Natural Cold Storage of Fruits and Vegetables by Mike and Nancy Bubel