Miscellaneous Questions about Earthbag Building
answered by Kelly Hart
Advantages of Earthbag Building
My Earthbag/Papercrete House
Interior Walls
Electrical
Plumbing
Floors
Stairs and Ramps
Structural Concerns
Moisture Proofing
Hanging Pictures and Cabinets
Retaining Walls
Planter Beds
Garden Walls
Problems with Varmints
Security
Radon
Temporary/Emergency Shelter
Retrofitting Structures
Rainwater Catchment on a Dome
Miniature Bag Kit
Costs
Patents
Advantages of Earthbag Building
Q: I am a junior at Black Hills State University, South Dakota and I am doing a class project on non-traditional homes and I have been selected to do mine on sandbag homes. A few things I am curious about is an estimate of cost, advantages and disadvantages.
A: As for cost, it can vary a lot, depending on design, size, and many other factors...but in general it can be quite inexpensive. We built our 1,250 sq. ft. domed home for about $35,000, with me doing most of the work. Certainly economy is one of the advantages. Another is the fact that a structure can be built with very little embodied energy that might have a negative effect on the environment. Also the bags can be stacked into domed shapes, eliminating the need for a wooden or metal roof structure, and require very little by way of a foundation to build.
Q: I am a family physician, part of the US Air Force. I am deployed to Afghanistan in its southern region currently. The province that I am located in is among the very poorest rural provinces here, and I am tasked with developmental work. The previous team here had an individual who got things going in the right track. When he left here a month ago he mentioned to me the idea of earthbag construction and maybe starting that project here in Afghanistan. They build most of their homes from dirt mixed with water and some kind of weed for a binder. What do you think about earthbag building here?
A: I think that earthbag building in Afghanistan could work out quite well. As you say, the vernacular architecture there is already earthen, so there should be little resistance to the introduction of a method that resembles it. While building with earthbags might be a little more expensive than what they are used to, it likely has the advantage of being quicker and probably more earthquake resistant. Also, the range of soils that can be used is much greater than with most earthen methods (adobe, rammed earth, or cob).
Q: Can you tell me how much to budget for a one bedroom earth bag construction home? The labor is free.
A: Earthbag construction can certainly be done for less than most methods of building, but it still costs quite a bit to finish any house. If you make domes, you can eliminate most of the cost of a roof. Earthbag construction does not necessarily need a conventional concrete foundation, which can also save a lot of money. Several years ago I built an earthbag house for about $16 a sq. ft....with my doing most of the work.
Q: I would very much like to know what materials to use for wind, fire and bullet proof when building my home...I feel we are fixing to be over run with gangs and I want to protect my family...I need a strong structure to withstand just about anything.
A: One of the best approaches to building a bullet-proof building is with earthbags, which is what the military has done for over a century. There is a blog about this very thing at earthbagbuilding.wordpress.com
Q: What are the pros and cons of earthbag housing when compared with traditional housing, rammed earth housing, and strawbale housing?
A: Earthbag building is more sustainable than most conventional building in the US because it minimizes the use of energy-intensive industrial materials, and can create very energy-efficient building shells. It is also more economical to accomplish, and takes less skilled labor. And it is remarkably variable in the forms that can be created.
Earthbag housing is similar to rammed earth housing, in that they both may employ the same type of soil to build the walls. On the other hand, earthbags are easier to fill and stack than creating forms for ramming and then actually ramming the earth. Furthermore, the walls can be curved, which is difficult to do with rammed earth. Also earthbags can provide either insulation or thermal mass depending on what they are filled with, whereas rammed earth is always thermal mass.
Compared to strawbale building, earthbags typically do not have the issues with moisture and rot associated with straw, so the building may last longer and be easier to maintain. When filled with crushed volcanic stone, rice hulls, perlite or vermiculite, earthbag walls approach the insulative qualities of strawbale. It is easy to create domes with earthbags, but not a good idea with straw; domes can eliminate the need for much use of wood and steel roof structures, and are therefore more ecological.
Q: How long does the typical earthbag house last?
A: Nobody really knows, since the use of earthbags for building structures like this has been attempted only in the last couple of decades. The polypropylene material, if kept out of sunlight, will last a very long time; moisture and rot are not generally a concern, and mineral fill material will not decompose. I expect the earthbag house that I built to last at least a century. In the case of filling the bags with cement-stabilized soil or good adobe soil, the bag material can actually be burned off after the house is built, because it is no longer needed structurally.
Q: Can the walls (skeleton) of a super adobe dome resist a lava flow without melting and collapsing?
A: It is an interesting question about the durability of earthbag construction in the path of a lava flow. I think it would depend on what the bags were filled with. As with any masonry material (like stone, concrete, bricks) earthbags that were filled with well-compacted and consolidated soil (like adobe or cement stabilized soil) should fair pretty well in these circumstances. Many people actually burn off the polypropylene bag material before plastering them, so obviously the bags are no longer essential to the integrity of the structure. But if the bags were filled with a looser material like gravel or sandy soil, and the bags were burned by the lava, then the structure might fail.
Q: My main argument for earthbags is durability. Through all my driving in the Big Island of Hawaii I don't see many homes that are more than 100 years old. Yet, it is very common to see 20 year old wooden homes rotting away in Hilo. To me, this makes them disposable homes. I have a hard time of thinking of them as fixed assets like gold. 5 years ago in California, I backed away just in time from buying a $800K home in San Francisco through a 30 year home loan. I said, whats the point of going through the aggravation of paying monthly installments for 30 years if the home is only going to last 20 years in perfect condition? ( I guess they can last longer if you spend a couple thousands in termite maintenance and painting every couple of years). And if I am thinking about transferring property to a family member, I would think they have to tear down an old wooden home when I pass away. So everyday that goes by, it is becoming harder for me to think of a wooden home as an investment.
A: (Molly Hart) I agree with you whole-heartedly about the sustainability issues around earthbag and other alternative building practices. It does seem crazy to build with wood where the moisture levels are so extreme, and termites are prevalent. All the lava is used for rock walls, and I haven't seen one home made out it. I have seen first hand what a short time of negligence can do in this climate to traditional homes.
Q: I live in Oregon and, considering the rain, I was wondering if earthbag building is suitable to this climate? Also, how long do you think earthbag buildings last?
A: Earthbag homes can do fine in wet climates, especially if you use a design that has a roof with eaves to keep the rain off the walls. Earthbag homes should last a very long time, if they are maintained...probably for centuries.
Q: I was wondering, why you choose earthbags over the other choices you have obviously researched.
A: At the time that I was designing my house, I also was exposed to a variety of interesting alternative approaches to building, and decided to experiment with some of them. I was intrigued with earthbags for several reasons: they can be filled with natural, earthen materials; they can be flexibly arranged into a wide range of shapes; if protected from the sun, the bags and their contents will not rot over time; they can be fashioned into domes, so that other tensile roof materials are not needed; they are inexpensive; they are simple to use without much experience.
Q: Could you briefly outline the main construction challenges of building your earthbag house?
A: The earthbag/papercrete home that I built was definitely experimental in nature. I had heard of the use of sandbags for building structures, particularly through the work of Nader Khalili in California, but all of his work was focused on using adobe soil, which solidifies into a solid block, so that ultimately the bag itself is not needed structurally. I wanted to fill the bags with an insulating material, because at over 8,000 ft elevation in the mountains of Colorado, the house would be comfortable. I chose scoria, a local light-weight volcanic rock as a filler material...but this had never been done before. With this loose material, the bag itself would become part of the structural fabric.
Another challenge was that my design called for a rather large (30' X 20') elliptical dome as part of the structure. This is larger than anything attempted before with earthbags, as far as I know. Would this be possible? I didn't know. At first I tried making this as a free-standing stack of bags...and it started to deform by the time I nearly had it completed. So I had to dismantle much of it and start over with a pole-frame internal support structure.
Another challenge was creating the arched span over the 6' doorways with earthbags...again something that had never been done before. Also I spanned the six-foot vaulted entry to the house with earthbags...not easily done.
Then there was the challenge of designing the two-story earthbag connecting space between the two primary domes with the entire earthbag portion both resting on the existing domes and on wood-framed supports on one side.
A whole other unknown was how papercrete would function as an external and internal plaster over the bags. This material is virtually untested in this application. Just making the mixer for the papercrete was a big job.
Of course another major challenge was that I accomplished virtually all of this by myself, without the benefit of a crew for assistance. It took me about three years to build this house.
Q: Are you happy with how your earthbag/papercrete house is working out?
A: I am quite satisfied with how our house is working. We have had no water problems at all. The papercrete has been holding up pretty well, but after about five years is showing signs of erosion in areas that are hard hit by storms. I would basically build the house the same way if I were to start over again today, although I might put a finish coat of harder stucco over the papercrete. Another change I would make is to make the larger dome circular instead of oblong, because the circular shape is much more stable and I wouldn't have to deal with the unequal forces that the oblong shape creates. I am especially pleased with the thermal efficiency of the house. It is comfortable both winter and summer. I'm sure this is because I filled the bags with the crushed volcanic rock that is available in our area.
Q: How do you heat your house?
A: The house is designed for passive solar heating, and that works pretty well when we have sun, but on extremely cold days, or during overcast weather, we have both a wood stove and a couple of small propane direct-vented heaters in the bedroom and in one of the offices. We also have solar hot water in the hot tub and preheating the domestic hot water, and this heat can also be used for supplementary heat.
Q: Is it practical for a man nudging 60 to attempt this project on his own? One advantage - unlimited time (I hope!)
A: Hey, I'm nudging 60 and I did it!
Q: I am interested in building an earthbag home. Are you aware of any builders who can construct a home in Florida? My husband and I saw your home on HGTV, but realize that it took you 3 years of working full time on your home. We would not be able to make that kind of time investment. If you have know of any builders to refer us to I would appreciate it.
A: It did take me that long to build my home, but I did 95% of it by myself, which most people wouldn't do. Earthbag building could proceed nearly as fast as other methods of building, if a crew is organized and experienced. Unfortunately finding such a crew would likely be difficult, because building this way is not very well known. The best you could expect is to find a local builder who is willing to help you and willing to learn how to build this way himself...or to train the crew yourself. It is not difficult to learn how to do, but does require some special knowledge.
Q: I have been considering taking a class at CalEarth on superadobe, but the price is quite hefty for someone my age (24). I have been checking out your site and thought I'd ask if you think it necessary to take this class or if it is also quite possible to build a sturdy earthbag home through book and internet research and experimentation?
A: I built my earthbag home without the benefit of one of the CalEarth workshops (partly for the same reason that you mention), but I am pretty comfortable with experimenting with various construction technologies and have a lot of experience in doing this.
Q: I am interested in combining homes of super adobe, bags, earth and papercrete. What kind of costs for about 800 sq ft?
A: Earthbag building can be one of the least expensive ways to go, since the materials themselves are fairly inexpensive. It is all of the other things that most structures need that add up to more money, so the walls are just part of the cost. I built my earthbag/papercrete house for $16/sf, about ten years ago...but I did almost all of the work myself, and I am very good at scrounging for supplies...and it took me three years to do so.
Q: Is it possible/recommended to use earthbag construction for interior walls?
A: You can certainly use earthbags for interior walls, but bear in mind that they do take up that extra space, and that if there is going to be much plumbing in the wall it is often easier to use conventional wood framing.
Electrical
Comment (Owen): Here's an easy way for mounting outlets. You can add just one piece of plywood to the side and place it at a butt joint. Nail or pin it into the end of a bag.
Response from Kelly: When I was ready to install electrical boxes in my house in Crestone, I simply drove some long pointed wooden stakes into the bags where I wanted them and left enough sticking out to screw the boxes to. With the scoria this was easy to do and they were plenty firm. This may be harder to do with some soils, especially if stabilized. Once the stakes were driven in they were amazingly firm and did not wobble, and of course the plaster holds them even firmer. Your method and Kaki and Doni's are likely more certainly secure, but the stakes have the advantage that they can be done later, when you might be more sure of where you want them.
Q: Should the plumbing be stubbed up in the floors or should it come from outside through the walls?
A: In my earthbag house I brought the primary water line in below frost level and then up to connect with plumbing in a framed interior wall. This avoids any issues with freezing pipes.
Q: I am interested in building an earthbag home. My question is about plumbing for the toilet and shower. How is the toilet plan setup and where does it drain to?
A: Typically the plumbing that you describe would go under the floor, in the ground, and be set in place before the wall building begins. The black water from the toilet needs to drain to an appropriate septic tank or sewer line. The shower drain could be plumbed into a gray-water tank for possible re-use if you want.
Q: I am considering a strawbale with an earthbag foundation. I live in Illinois...cold winters wet spring. My question is, can I use a radiant heat system between the earthbags?
A: Radiant heat works best when imbedded in a solid thermal mass floor, such as adobe or concrete. If you want to embed radiant heat tubes between the earthbags, this might be possible, but I am not sure how well it would work. The bags would have to be filled with good adobe soil and well insulated on the outside.
Q: What is used for the slab inside the the outer walls? I have no idea of what would work other than concrete. If there is something else will carpet or tile be able to cover it?
A: A concrete pad is certainly one option, but is not the only one. The floor could also be made with flagstone, brick, pavers, poured adobe or rammed earth. Carpet could be laid over any of these, but tile would need a solid concrete base most likely.
Stairs and Ramps
Q: Have you seen any plans that would work for a wheelchair ramp made of earth bags? The house level is about 4 foot high. My wheelchair bound grandson is now with me. I am also disabled. This is the only construction I think I could manage, physically & financially.
A: I have made steps with earthbags, but have never tried to make a ramp. Stacking bags naturally creates a stepped shape because of the discrete bags. If you want to make a smooth ramp out of this, you would have to fill in the steps with concrete or something like that. Or I suppose you could make a stepped form with earthbags, and then cover this with wooden boards or metal to make it smooth....but that sounds like a lot of work that might be easier done with entirely wood or metal. Or, here is another idea: suppose you created two stepped earthbag walls with a space in between them that was then filled with earth, tamped as a ramp and covered with a few inches of concrete? Something like this might work.
Q: My son is concerned that the 'pumicebag' walls won't be strong enough to support a flat concrete roof which, in turn, won't be able to support the weight of floor tiles and people sitting up there. Kelly, I am now incredibly worried and implore you PLEASE, to give us a second opinion on this important point before we start building.
A: If you carefully tamp the bags into place as you lay them and make the reinforced concrete ring beam at the top of the walls, you should have no problem from subsequent settling. Bags of pumice, especially once they are plastered are plenty strong enough to support your roof structure.
Q: Starting next summer, my family and I will be building a below-grade earthbag structure, made of several connected domes in the north, where it is very cold in the winters. I was curious if we needed to plaster it, given that it will just be backfilled anyway, or if we could just superbly waterproof it (6 mil poly sheeting). Did you plaster the side you bermed? Any idea how many feet of earth we can safely put on it?
A: I see no need to plaster earthbags before backfilling, but the poly sheeting is definitely a good idea; I actually used two layers of plastic over my backfilled earthbags.
As for how much weight can be placed on an earthbag dome, you would be exploring somewhat uncharted waters here, so I caution you to be very careful. I did cover my underground dome pantry with about six inches of earth and heavy gravel, and it held up fine. It is kind of tricky, because the steeper the dome is, the stronger it will be to withstand downward pressures, but also the steeper it is the harder it is to get soil to stay on top of it. I ended up with about a 45 degree earthbag roof on my pantry which was reinforced underneath with the pole rafters bolted into a ring at the top. You might consider some sort of an arrangement like this ..and also talk to an understanding engineer...or at least do some experiments before committing to an entire house like this.
Q: On a rectangular earthbag wall I would like to have a tiled roof. How to do that (with long eaves)?
A: The roof structure on a house with vertical walls is likely to be the same as a conventional house, with trusses, rafters, or SIP's...and yes, long eaves is a good idea.
Q: We would very much like to have our house design incorporate a basement, to take advantage of the temperature differential and also to gain the greatest possible space for the least use of materials. Are earthbag walls suitable for basements, perhaps if wrapped on the outside with a 6mil polyethylene or something similar?
A: I think that earthbags are especially well-suited for below-grade walls. The earthbag house I built in Colorado was substantially bermed into a hillside, and I just used two layers of 6 mil polyethylene as a moisture barrier before backfilling. Obviously the walls need to be sufficiently curved or buttressed against the lateral pressure from the earth.
Q: I really liked the little dome house in Mother Earth News Magazine. I want to build these little houses for my mini goats...they would just love them especially the grass roofs to graze on. Would these little houses be able to support goats walking on the roof without collapsing?
A: (Owen)
Domes are the strongest shape in nature. There's already many tons of soil on top and many more tons could be added with no damage. So there's little worry about a dome like this collapsing from animals walking on it. There's a much greater risk of damage from their hooves puncturing the plastic. This is what you need to be concerned about. The soil on top is very thin -- just a few inches. The steep slope makes it difficult to keep soil on top. Rain keeps washing it downhill. For this reason I do not recommend building these domes for goats as you describe. Unless you can figure out a way to add lots of soil on top and keep it up there, the plastic will be close to the surface and vulnerable to punctures.
Q:
In my opinion, there is a contradiction between this : "Super Adobe homes are strong, and can be wind and waterproof. Designed to be resistant against extreme environments, they have been earthquake tested to 6.5 on the Richter scale, complying with the most rigorous earthquake building codes."
And this : "Just how resistant earthbag housing might be to earthquakes is not known for sure. Very little testing has been done to prove this one way or another. This initial seismic tests done at CalEarth and other places are encouraging, but not conclusive" http://earthbagbuilding.wordpress.com/2010/01/21/responding-to-catastrophe/
A:
As with everything , there a lot of opinions out there. The quote from the page about the Pegasus project are not my words; they stem from literature put forward by CalEarth, since Nader Khalili was the architect involved with that project. His assessment is based on the testing that was done in the 90's on a small dome, as part of the process of permitting a larger project for the City of Hesperia near CalEarth. While I agree that the results of this testing are impressive, and that domes of this configuration do seem to be extremely durable, I know at least one engineer who questions the validity of these tests. Furthermore this testing was only for a small dome, not any vertical-walled structure, so one can't necessarily extrapolate that all earthbag building would be equally durable...there are just too many variables. Therefore I do stand by my statement that you quote above. I would hate to advocate something that is eventually proven to be inadequate; the consequences are too risky.
Q: I am interested in building an earthbag home and would like to berm it more than you have because, well, this is Texas and we are very hot and humid in my location. How did you battle moisture from berming the home against the earthbags?
A: I used a double layer of 6 mil polyethylene plastic where ever I intended to berm the structure. As I was building up the courses of earthbags, I simply tucked the plastic between the courses a couple of bags higher than where I knew the soil would come to, and let it dangle downward until I could do the back filling.
Q: I'm wondering if the earthbag technique, or a form of it, has been tried in the Pacific Northwest, where wet winters are the norm.
A: I am not aware of any earthbag structures built in the Pacific Northwest, but there likely are some. While it is true that most earthbag buildings have been built in more arid locations, there are some in wetter climates, such as Thailand, Hawaii, Mongolia, Belize, Honduras, Haiti and the Philippines. I might suggest trying a more conventional vertical walled structure with a roof that has good eaves to shed water away from the walls, rather than a dome building that takes the full brunt of the storms on the earthbag wall. There have been some successful earthbag domes built in wet climates though.
Q: What is the best way to waterproof an earthbag home in a hot, humid climate (we get about 40" of rain here annually and relative humidity is rarely below 80%)?
A: The best way to finish an earthbag wall in a hot humid climate is, first of all, keep as much water off the wall as possible, with a good roof with an eave. Next, do NOT use a moisture barrier; leave the wall as breathable as you can. And use a natural earthen plaster, especially on the inside. It has been proven that earthen blocks (adobe or CEB) handle hot humid conditions better than any other type of wall system. The clay in the earth will actually help absorb and release humidity while keeping the interior temperature much more stable and moderate.
A: Upper kitchen cabinets - are they installed on the walls in a special manner? They could be fairly heavy with dishes, cups, etc. Don't know much about installing cabinetry, but I'm wondering about anything installed on the interior walls. Normally, you find a stud and pound in a nail or screw in a screw. Won't installations on earthbag walls make holes in the bags within? Does this cause problems, and will heavier items be stable?
A: That is an excellent question about how to attach cabinets to an earthbag wall. The answer, to some extent, depends upon what you fill the bags with. If you were to use an adobe-like soil that contains some clay, then you can actually use very long screw that will hold quite a bit of weight. With other, looser soil or material, you need to use another strategy. You can easily pound long sections of threaded rods all the way through these bags, and then bolt sections of wood (even 2" X 4" s) on both sides, that are very secure. If they are long enough, a whole row of cabinets can be hung on them. Piercing the earthbags, even with such loose material, is not a problem. I filled the bags of my earthbag house with scoria, a type of crushed volcanic rock, that provides excellent insulation.
Q: We have a large number of framed photographs of our forefathers / gods to which we pay our respects often . We have to have electrical fittings / plumbing fittings which require to be fixed on the wall. Since we don't get good quality PVC pipes / fittings in our area, we often have leaky taps / joints which are to be serviced every now and then which makes closed / consealed piping undesirable.
A: When I built my earthbag house I drove large wooden stakes into the walls wherever I wanted to attach electrical recepticles and then screwed the electrical boxes to these. You can also attach longer pieces of wood with wire or twine in any area where you think you might want to hang pictures. As for plumbing, I tended to place the bulk of it in hollow wood-framed interior walls which allowed access, or just drove the pipe through a wall when necessary to go from one side to the other.
Q: On a completed house, will the walls be safe to drill or put nails into for some interior decoration?
A: How to attach interior fixtures depends partly on what the bags are filled with. If you are using a solid adobe-like soil, then you might be able to use long decking screws to make some attachments. Otherwise, you might need to imbed wooden anchor boards or stakes into the bag walls to give you something to screw or nail into. It is also possible to pound long threaded rods all the way through a wall to secure heavy items.
Q: I am looking for information on building a retaining wall out of stacked bags of concrete. Any how-to information you could provide would be great.
A: You can certainly make a retaining wall with bags of cement stacked up, but I might suggest a simpler, cheaper, and more sustainable approach to making such a wall: just use earthbags (polypropylene bags) filled with your local soil, stacked up like you would with bags of cement (laid in a staggered, brick-like pattern). If the wall is curved against the soil being retained it will be much stronger. Two strands of barbed wire placed between each course also makes it stronger, but this may not be necessary. The earthbags will need to be plastered with stabilized earthen plaster or stucco to keep the sunlight off of them and make it look nice, but so would the sacks of cement approach, and this would use way less Portland cement, which has an environmental toll.
Q: I have been looking for an alternative way to build a terraced/retaining wall system for a slope adjacent to my home that has "slumped" over the years. All the traditional methods, such as timbers, block, Keystone systems are much too expensive. I stumbled across your site this morning looking for alternative building techniques and noticed your article on earthbags. Have you used earthbags for this application or might you suggest other methods?
A: Earthbags are an excellent choice for retaining walls. I once built a dam with earthbags that held a large body of water. For such a wall you should be able fill the bags with your native soil. It is important to keep the polypropylene bags shaded from sunlight exposure, so they must be eventually plastered with stucco or something.
Q: Can one build a retaining wall with earthbags similar to a retaining wall constructed out of tires?
A: This is done much easier with earthbags than with tires.
Q: I'm planning on building an earthbag garden wall at my house in southern Oregon, maybe fifty feet long, enclosing a small hillside area on three sides. The bags I want to use are 12 inches wide when filled. Is that wide enough if I stack them carefully and bind them well with the barbed wire for a 5 foot wall? (I'd like to make it relatively narrow.) And I suppose I'll punch in some rebar through the top courses to stabilize it.
A: As for bag size, I would think that a 12" thick, 5' high wall would be plenty stable. You might want to either make it curved some or provide some buttresses to make to more stable. Also, in areas where it might be bermed on one side, you can lean it into the berm some. Normally rebar stakes are not necessary, but they will do no harm.
Q: We are planning to build four small and cheap houses using strawbales. The north wall of the houses will touch the wall of a ground. We are thinking to build a retaining wall against this land using superadobe technology. This wall would be covered with something not permeable as is usually done. We have seen in your website that you advise using earthbags for retaining walls. What we are trying to calculate now is the exact measure of the curvature to make the retaining wall resistant enough. In our original plans we already considered a curvature in the plan of the wall (overhead view), but we don't know how much curvature it may have. Another question is the bag size. Our wall is 16 m long and 2 m high and our local soil is basically clay.
A: From what I can see, your plan looks good. The curvature of your north wall is probably adequate, but if it were me, I would make the arc a little more (use a shorter radius), just to be sure. As for bag size, the standard size that we recommend for earthbag construction should be fine: 18" x 30" (46 cm X 76 cm) measured when empty.
On the subject of planters/raised garden beds - would you recommend plastering the inner vertical surfaces that will be in constant contact with moist soil?
A: With planter beds, it doesn't really matter if the bags or their fill material gets damp. But in terms of protecting the bags from wear and tear and abrasion over time, a good solid plaster is a good idea...and the bags need to be protected from the UV in the sun. I would recommend a cement-based stucco below grade.
Q: Just wondering if the rice bags are biodegradable enough to use as a base for garden beds? I use cardboard often, but have quite a few bags and thought that might be a good use for them.
A: The only thing that I know that degrades polypropylene is the UV in the sunlight, but underground they do not generally degrade.
Q: I'm looking into building a simple fence/wall using your technique, but can only find small garden beds or home plans. Is there a plan for simple fencing?
A: Making an earthbag fence or wall is a fairly simple project. You can usually use the soil that is on-site, and use the same technique for stacking the bags that you would with a larger home or a small garden bed. It is better if the path of the wall is curved to give it more stability from toppling over. If the wall is straight for over about 8 feet, you might need to buttress it for support, depending on the height of the wall. Standard 50 pound bags can probably be stacked up to 2 or 3 feet without the need for buttresses, but above that it would be a good idea.
Q: Can you please advise me how rodent proof is earthbag construction. In an area where there has been considerable drought, would the bags themselves be an attractive way of getting nesting material?
A: Most earthbag construction is inherently rodent proof, much more than strawbale, or stick frame construction is. The mineral material filling the bags is not attractive to such critters, and the bags themselves are usually not accessible because of the plastering material. We have had NO mice coming through the walls of our house.
Q: My husband and I are planning to build our home out of sand bags. We have virtually no budget and were planning to use either the dirt on our land or silica sand. It must be strong enough to withstand anything a tornado might throw at it and we feel it will. Our BIG problem is fire ants. I am allergic to the bites and we need to know if they can or will live or get into the walls using either of these materials.
A: Ants do live in soil, so this possibility couldn't be ruled out; I would expect that this situation would be very rare, and could be dealt with in a variety of ways to kill the ants if they started to establish a colony.
Q: I was wondering how to prevent the bags from becoming infested with all sorts of ants and pests?
A: Clay/sand soil will form a solid block like adobe. Either this or cement-stabilized soil is not so attractive to ants and other pests. Also, the bags are well plastered both inside and outside to form an additional barrier.
Q: The area my friend wishes to build on is prime scorpion habitat, not to mention the ever-present fire ants that love building nests in dirt. How do you keep earth-dwelling insects out of a house made of dirt?
A: The polypropylene bags have a pretty tight weave, so this alone will keep scorpions and some ants out. The first few courses of bags should be filled with gravel, which does not attract ants, and then with a good exterior plaster (perhaps lime), I don't think ants will be much of a problem. If they do appear, there are ways to exterminate them...so I wouldn't worry too much about this.
Q: I live in Florida and we have Fire Ants. I just worry that the ants would love these types of houses and infest the walls and make it into a giant ant hill. Have you ever had anyone have problems with that? I know you could probably spray bug killer but I can't do that ifIi am gonna have my goats in them.
A: (Owen) Fire ants: add lime or cement to the mix, plus maybe some borax. This would turn the soil in the bags rock hard. They may make nests on top, however.
Q: On your Web site you say earthbag is bulletproof. Where is the proof? This is not an idle question. There have been a number of murders here recently that could have been prevented had the people been living or studying in bulletproof structures. There is interest here in building with earthbag for this reason, but first I am checking with you to see if you are aware of any ballistic tests that have been conducted on earthbag walls, and if the results are published, where I could get them. Thanks very much, from the war zone in Israel.
A: This is a very good question. I only inferred that sandbags are bulletproof from the fact that they have been used to barricade military encampments at least since WWI. I'm sure it makes some difference what the bags are filled with, how impervious to bullets they would be. I suggest seeking some military training manuals for more information about this.
C: I would like to congratulate you for your contribution to the world's various societies on this construction technology. I am living in East Africa. Let me tell you something. The villagers of one remote area had difficulty in constructing concrete buildings because the sand in the area was too salty for Portland cement applications. Their houses made of mud and wood were unstable and they were frequently becoming prey to wild animals, i.e. leopards and lions. Using information from your web site, I managed to construct a circular earthbag house roofed by corrugated iron sheets. This technology was appreciated and many villagers applied it for their houses and the problem of man eaters was solved. I then thought that it will be good to return our thanks to you for saving the lives of many villagers. Although we do not have money to pay you back...but God will reward you.
Q: I am moving ahead with using scoria in the north walls of my earth bag home. Just wanted to check in with you about Radon. Have you ever done a radon test in your home or know whether or not this is a potential issue?
A: Yes I did run radon test in my bedroom, since it is the smallest dome and is completely surrounded by bags of scoria, and a local person was telling people that scoria out-gassed radon. The result of this test was a very slight degree of radon, but not enough to be concerned about. I was relieved that this is obviously not a problem. But I would recommend putting a radon barrier under your floor, or mitigating for this potential, since this is a much more likely source of this.
Q: You talk about going into the back country with some empty bags, some plastic, and a shovel and being able to build a quick shelter. What is the plastic for? Is that just for waterproofing?
A: The plastic would be for waterproofing, and also to make windows or doors that let in the sunlight.
Q: After viewing the simplicity and ethical way of construction this seems to be a viable way of adding and enhancing an older mobile home with the final product being the mobile walls and ceilings eliminated.
A: As for using earthbags to retrofit an older mobile home, this does seem viable, although I would likely consider covering the walls from the outside, and retaining the interior finishes. Otherwise you might not end up with much space inside.
Q: We would like to build in such a way that our structure is somewhat modular/expandable ... this seems more efficient to us. Aside from planning things like door and window locations with future expansion in mind, I'm wondering if there are any other things that need to be considered. In particular, I'm concerned about how one would tie a new wall into the existing structure to make it a monolithic whole.
A: Making additions to an existing earthbag structure this can be done, but it is generally best to plan for this in advance by creating a doorway for the eventual passage first, and just filling it in with temporary bags, so that it is easy to push through later without needing to tear into bags and wire. A new wall could be tied to an existing wall with rebar pins if necessary.
It is the rebar pins (or whatnot) that worry me, as it seemed to me that the seam between the old wall and the new (where there could not be a running bond) would be a critical weak point. One method I thought of would be to make a one bag buttress where I knew the new wall would go, with half bags in every other layer. Later on, I could strip off the plaster, knock out the half bags, and wedge new bags in (filling them in place I guess). That seems awkward, though. Using rebar, how would the pins be oriented? Just rammed diagonally through the bags of the new wall into the old?
Your buttress idea is a good one, if you can work this into your plan. Rebar pins diagonally is what I pictured; this would not be as strong as interlaced bags, but if it were done on every course it would be pretty secure. Another thing you could do is connect the two walls with wire mesh on both sides that wraps both walls before plastering.
Q: I have a small rock cabin in Spain that we want to enlarge using earthbags. Is it possible to raise the roof by adding earthbags on top of the existing rock walls? (The width is almost exactly the same as a 25k polypropylene bag.) If we want to build an addition to the rock cabin what do we need to do to make sure the earthbag wall doesn´t separate from the rock wall?
A: I see no reason why you couldn't extend your rock wall with earthbags. To connect an earthbag addition to the existing stone structure I would suggest that you create a strong physical bond with a series of anchors embedded in the stone wall that are also embedded in the earthbag wall. This could be done with pieces of steel bar that is pounded into holes drilled in the mortar line between the stones in several places.
Q: Do you have any thoughts on how you could integrate a roof rainwater catchment system with an earthbag dome structure? Have people done that before?
A: I did have some discussion with another person about the possibility of rainwater catchment on a dome, and had some specific suggestions. I was imagining a way of creating gutters that circled the dome at some level above the doors, possibly using large diameter black plastic pipe that was cut in half lengthwise and then attached to the dome and plastered into place with the exterior plaster, which would probably have to be a cement-based stucco to shed the water well enough. Some experimentation is certainly in order.
Q: How did you make the model kit of earth bags? (what materials for the bags - did you find anything in the right size easily available?)
A: We actually sewed the miniature bags from strips cut from an old sheet. Once the pouches were formed, we used a spoon to fill them with sand, and then folded and stapled the remaining seam. We created several half bags to use where appropriate.
Q: We would like to built in the future some of these buildings in Africa. What is the average cost of a school type building?
A: It is hard to say how much a school type building might cost where you live. Certainly building with earthbags can be less expensive than many other methods of building. Often the earth at the building site can be used to fill the bags, and even used as part of the plaster over them. Other things like doors and windows will cost about the same no matter what type of building your are making. Also, if your design is a dome, or a series of domes, then you can avoid some of the costly materials of common roofs.
Q: Any idea how long an earthbag house would take to build?
A: With an experienced crew, a small earthbag project could be finished in a few months...it all depends on how well the laborors work and the complexity of the project. It took me three years to build a fairly large house, but I did most of the work myself.
Q: For some time now, Legacy Constructions has been interested in the “earth bag” concept and are considering employing the concept in the construction of our upcoming projects in East Africa. The projects will be aimed at reducing the cost of construction for prospective home owners. Before we draw on the “earth bag” idea, we feel it is only prudent to ask for the particulars of the patent held on the concept, if any. We therefore, humbly request you send us a copy of the patent, or direct us to where we may obtain it, for our own scrutiny and records. We hope there will be no legal repercussions, should we decide to employ the method.
A: In 1999, Nader Khalili did obtain a US patent on his "Superadobe" concept which is basically what we now call earthbag building. His patent can be seen at patft.uspto.gov. Since this patent was issued he has stated that "Superadobe is a patented system freely put at the service of humanity and the environment. Licensing is required for commercial use." Actually this patent should never have been granted, since Mr. Khalili had extensively publicized exactly how it was done for over a year prior his applying for it. When his organization tried to get me to sign a contract for publicizing it through a DVD that I produced, I objected, stating that it would never stand up in court...and they stopped trying to enforce it. I wouldn't worry about this patent, especially now that Nader Khalili has died.