Miscellaneous Questions about Earthbag Building
answered by Kelly Hart
Advantages of Earthbag Building
My Earthbag/Papercrete House
Interior Walls
Plumbing
Floors
Structural Concerns
Moisture Proofing
Hanging Pictures and Cabinets
Retaining Walls
Problems with Varmints
Security
Radon
Temporary/Emergency Shelter
Retrofitting Structures
Rainwater Catchment on a Dome
Miniature Bag Kit
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 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.
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: 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.
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: 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.
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: 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 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: 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: 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.