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Hybrid Questions and Answers Involving Earthbags

Kelly Hart is your host at greenhomebuilding.com, and has built his own home using a hybrid earthbag/papercrete technique, which can be seen on the Earthbag page. He has adapted the concepts popularized by Nader Khalili and his "superadobe" building, by filling the bags primarily with crushed volcanic rock. This creates insulated walls that are similar to strawbale, except that they are completely impervious to damage from moisture, insects or rodents. The earthbags are plastered both inside and outside with papercrete. Kelly has produced a video, titled Building with Bags: How We Made Our Experimental Earthbag/Papercrete House, which chronicles the adventure of building this house, and shows other earthbag houses as well. Another video program that he produced is A Sampler of Alternative Homes: Approaching Sustainable Architecture, which explores a whole range of building concepts that are earth friendly. One of the homes shown in this video is a hybrid strawbale/wood framed home. Kelly spent many years as a professional remodeler, and is available to answer questions about what he has done, or consult about other hybrid projects.

Questions and Answers

Strawbale/Tires/Earthbag

Stud Wall/Earthbag

Earthbag Sauna and Kiva

Papercrete/Steel Quonset Vault/Earthbag

Tire/Strawbale/Earthbag

Strawbale/Cordwood/Earthbag

Earthbag/Driftwood

Concrete Block/Strawbale or Earthbag

Plywood/Strawbale/Earthbag

Timber/Strawbale/Earthbag

Stone/Adobe/Earthbag

Papercrete/Earthbag

Container/Earthbag

Geodesic/Earthbag

Strawbale/Earthbag

Q : We are working on a hybrid of ideas for a building ... a house with one back room 16' in diameter circle two stories tall, the first level back wall built mostly into the hillside, so we figure to ram earth tires till grade or just above, then earthbag, superadobe to reach proper levels to put strawbale on top. My question arises with the bond beam between the first and second floor and the roof; it is a load-bearing bale house ... ideas we have: 1. poured concrete bond beam (lots of money and not that ecological by our terms, 2. superadobe earthbag (strong enough?) 3. a re-salvaged welded metal I beam (too much?) any thoughts also in the back wall we wish to build a root cellar into the wall tries, ok ?

A : It sounds like you have an interesting project. I have several thoughts about what you describe. First, I wonder why bother with pounding all of those tires when earthbags would do the same job much easier? You can bury an earthbag wall just as well as a tire wall, especially when the wall is curved, as yours will be. You just need to bring the wall up high enough to be above grade to begin your strawbales. In this instance, I don't think there is a need for a bond beam...unless you are dealing with code officials who might have other ideas. The barbed wire between courses of bags acts much the same as a bond beam. I did something similar in my house, where the first floor is completely bermed on the north side; I simply made a skirt of 2 layers of 6 mil polypropylene draped over the back of the bags before backfilling. You might want to insulate with blue board or something back there, if you don't fill the bags with crushed volcanic rock as I did.

To make an entrance into the pantry, using bags would be easier than tires because you can easily make an arch with the bags over the entrance, and making half bags is probably easier than making wooden fill blocks for half tires. For the second floor, you could start stacking the bales right on the earthbags once you have an even bag surface above the joists. If it were me, I'd just continue the wall with bags, since it might be easier than making a circle with bales, but I'm partial to that technology. You will want some sort of bond beam at the top of the bale wall, which is usually done with wood planks, but isn't so easy with a circular building. Probably a poured beam with rebar and cement would be the easiest. I wouldn't rely on superadobe for a bond beam in this application. Salvaged metal might work, but it would be hard to get enough surface to not sink into the bales. Again, if you went the whole way with bags, you wouldn't need the bond beam.

Q : I have yet another question, and I know you suggest the earth bags all the way up but if I did stack bales on top of the bags would the bags act to wick up water into the bales? Also a man out in New Mexico was using recycled latex paint mixed with organic blown insulation to a paste consistency and was using this painted on a bale roof and till this point no problem... I want to say at least one year if not three. He actually mudded it like it was mortar. What are your thoughts on this as waterproofing if any? And also there is an earthbag house in Colorado they call the beehive that is having problems with the earthbags in the foundation leaking water. You have no such problem because of the liner eh?

A : Earthbags used as a foundation for strawbales are usually filled with gravel, which does not wick water. Other earthen materials might wick some water, but you can stop this by simply putting a moisture barrier between the bags and the bales. The problem with waterproofing strawbales is that it stops them from breathing, which is generally essential to assure that the bales stay dry. Any moisture barrier runs the risk of creating a surface where moisture can condense from the inside. Using bales as a roof is very difficult for this reason.

I don't believe I am familiar with this beehive house. I haven't had problems with leaks in mine. The only place I used the plastic liner was where I bermed soil up against the bags, otherwise my house is completely breathable. With the papercrete plaster, the water never has a chance to find its way through the bags, at least in my climate. Without knowing the specifics of the problem you spoke of, I wouldn't know what to say about it.

Q : I was also pleased to hear about your passive solar performance. I would like to have enough windows for light and passive solar, but blending in to my environment is important to me (one reason for my berming low into a hill), and huge banks of windows are hard to do that with. I have seen various"formulas" for determining the proper amount of window square footage for passive solar, ranging from 10% (of floor square footage) to 20% (and the 40% as you mention). Do you have any idea what you ended up with?

A : A quick guess is about 30%. The colder the climate, the more you need.

Q : Also, I was intrigued by your scoria there again. The naturalhouse.com guy isn't too hot about strawbale homes, claiming they lack the thermal mass for effective passive solar. You talk about your scoria having insulation qualities comparable to strawbale, but you obviously have sufficient thermal mass as well. Maybe it is that air space in scoria again--good for the insulation, but still plenty of igneous rock mass for thermal mass.

A : I wouldn't expect much thermal mass from the scoria. My mass is in the flagstone and adobe floor, and in portions of the house where the earthbags were filled with the sand. Whenever I could isolate these bags of sand in the walls, I did so. For instance, the first two or three feet of the bermed wall is made with bags of sand, and then this is insulated with more scoria on the outside, before it was backfilled. Also the entire landing from the main entrance to the house is created with bags of sand. Most of the internal papercrete plaster has a lot of sand in it also.

Q: I'm looking at buying a half-built earthship and have a couple questions. The site has 3 U's with about 5 ft. of tires, pounded with earth. Could you finish the rest with strawbale, 3-4 bales of straw?

A: You could certainly do this as long as the strawbales are completely above grade (not bermed). Tires have been used many times as a foundation for strawbale structures.

We're thinking about pounding rebar in and putting strawbales over the rebar. Would that be enough to support the roof or would you also want to add corner posts.

Pinning the bales with rebar is a good idea. Strawbales can be used as load-bearing walls, but this takes some care to allow them to compress some before plastering (or pre-compressing them with tensioned straps.)

Also the U's are not very curved so I'm a little concerned about the support of the berm on the north wall. Could this be solved by not building up the north berm as much?

Yes, although it doesn't take much of a curve of the tires to be very stable. If you decide to complete the walls with strawbales, then you wouldn't be berming up above them anyway.

If we increased the curve on the next couple of tire courses would that help?

I suggest that you keep the curve of the wall consistent and keep the walls vertical.

Q: I'm struggling to know whether to pursue bale or earthbag construction, because our site is a VERY windy area and has lots of moisture, so bale construction isn't very conducive, as the shear strength against the wind can be lacking. However, the insulative value is the primary concern that the development has in the construction of this shelter, which puts the earthbags lower on the scale. I read about your home in Colorado, but we don't have access to Pumice where we are located. Have you ever heard of projects that combined the two technologies to gain better structural support, while maintaining the high insulation value?

A: I don't know of any hybrid earthbag/strawbale buildings, but this is certainly possible, although the walls would be mighty thick. If you try this, the straw should be on the outside with the thermal mass on the inside for comfort and efficiency. Other natural insulating materials that can be used for filling earthbags are rice hulls and perlite.

Stud Wall/Earthbag

Q: I already purchased a foundation/framed/roofed house and am planning to use the bags between the studs. I have a question about the breathability of the walls and the papercrete application. You said you added Portland cement to the mix. I heard that the cement hinders the breathability of the wall.

A: There is a big difference between the breathability of concrete stucco and papercrete. They both use Portland cement, but papercrete is much more porous and breathable, whereas cement stucco doesn't breath very well.

Q: Also, what is the cost of the papercrete as compared to applying a cob mixture over the sandbags?

A: It is difficult to compare the costs because there are too many mitigating factors. Do have a mixer for the papercrete? Do you have good clay and sand nearby for the cob? Are you going to mix the cob by hand, or will you be renting equipment to mix it? I believe that the papercrete might need less maintenance over time, which might be a factor.

Q & A:My husband has built a small stick frame house. We built it before we knew much about alternative methods. We had always talked about building something different, but we were a bit wary of the learning curve and lack of experienced builders in our area (NW Louisiana). Since my husband's father built in a similar way we had his expertise on hand. We are now at the stage where we were about to put in fiberglass insulation in the walls and rough-cut cypress on the outside.

Having lots of good insulation in the walls and roof will be imperative for comfort. There are a variety of green insulation alternatives you might consider, besides the fiberglass: see this page.

Now, I may be crazy, but I am trying to convince my mentally and physically weary husband to switch gears and go for something that will help us utilize the energy of the sun for heating as well as keep us cooler in the many hot humid months without using as much energy. Did I mention that we are almost out of saved money and will soon need to return to work? We are looking for alternatives that are dirt-cheap.

Your motives are right on as far as wanting to heat and cool naturally, without paying for heat and air conditioning.

This is what I am proposing. 14 x 20 PP rice bags with local earth will wrap our 20' x 32', two-story house.

While doing this would probably help keep you more comfortable inside, I think there might be better ways. Putting all that thermal mass outside the insulated core won't buffer temperatures nearly as much as if the mass is located on the inside. I might suggest that while you are still at this framing stage, you might be able to redesign the windows some so that you have a somewhat passive solar house. In Louisiana you don't need very much solar gain...just a modest amount. You might study passive solar designs some.

And we would cover it with several inches of clay plaster mixed with rice hulls that we can hopefully get delivered cheaply (It doesn't seem we have much straw around here).

I don't think the rice hulls would help much with the plaster, since they aren't long enough to bind it. But you don't necessarily need the straw, either. If you want to proceed with the exterior earthbag idea, you might consider filling the bags with the rice hulls...then you would have some super insulation.

We currently have all of our windows and door installed, should we create arches or triangles over the opening or will wooden or metal supports work?

Any of those are options, especially if you use the relatively light rice hulls in the bags.

What would be the easiest and/or cheapest route?

Depends on several factors...certainly the triangles or arches might be the cheapest, but not necessarily the easiest.

How would we allow for other additions to connect to the structure (like a porch for example)? How would you start the foundation of the earthbags? We have a reflective metal roof and 8' rafters. The roof has a very gentle slop and we were considering no crawl space.

You have a lot of questions...perhaps you should find one of the earthbag books to help you with all of this listed on this page.

 Do you have any insulation recommendations for the roof between the rafters?

See the above comment about insulation.

Do you think there are any extra considerations when creating an earthbag wall of this type--because, for example, one cannot access the inner side of the stacked bags?

Access to one side shouldn't be a problem.

How much overhang to your recommend beyond the earthen plastered walls? We get about 50 inches of rain here year.

Maybe 18" would be good.

One of my husband's main concerns about the earthbag wrap is structural safety. He is concerned about hundreds of pounds of earth stacked two-stories high falling away from the house and crushing someone or some thing. How can we safely and not too expensively connect the earthbags to the house structure?

I would still use the barbed wire between the courses to keep the whole thing as one piece...and then also periodically tie the bag wall to the wooden one with some sort of metal strips or wire tied around some of the bags periodically.

Have you heard of anyone else wrapping a house in earthbags?

No, but I have considered doing it myself.

He is also worried about the time it will take with one or two people and occasionally a couple others working on it (but mostly just my husband).

His concern is perhaps justified, in that doing this would definitely add quite a bit of time to your project, in terms of figuring it all out, teaching yourselves how to do it, making some mistakes and having to do it all over again, and then finally plastering the whole thing with earthen plaster, which is quite tedious in its own right.

If I were in your position, I would be tempted to do things in a simpler way: make sure that you have some passive solar heat gain for the winter, insulate everything as well as possible, place a fair amount of masonry materials on the inside, such as interior brick or rock walls, tile floors, etc....and enjoy your new place the way you originally intended, without too much more fuss.

Q: We live in Central Washington State and own a nice manufactured home. I am wanting to go greener but I really do not want to start over completely since I am happy where I am at. I was wondering if it would be possible to wrap the existing home in earthbags to make it more efficient? I imagine that a vapor barrier may have to be placed between the existing siding and the earthbags.

A: This is certainly a possibility, especially if the earthbags were filled with an insulating material, such as crushed volcanic rock, perlite, or rice hulls. There are a number of technical details that would need to be worked out, like proper foundation, roof overhang, and how to deal with windows and doors. A vapor barrier between the earthbags and the siding may not be a good idea, because it could become a point of condensation that would adversely affect the siding and interior insulation. It is usually better to leave the wall system as breathable as possible.

Q: I have built a 32' x 40' pole barn structure. It consists of 10' C channel studs (1/8" thick metal 2" x 6" - they were cement forms). There are 5 studs on each 40' side with a top plate. Studs are 10' apart setting on 2' x 2' cement pads 1' deep. There is a truss atop each pair of opposite studs of the same C channel spanning the 32'. Above perpendicular 2" x 6" wood roof rafters support R panel roofing with a 1' eave. No walls yet. I think I may change the roof to a living roof of 2" Styrofoam panels, vinyl, some free plastic mesh belting, 1" to 2" light weight cement, 6" light soil? I would like to build the North and West walls up to the 10' top plate with earth bags filled with a fine Padina sand that covers the entire 10 acres here in central Texas. I plan to double bag the first course. I wonder if this 10' wall will need external and internal buttress and of what height?

A: The 10' spacing on your steel studs should provide enough strength without extra buttressing, as long as the bags that are in contact with it are firmly connected to it, perhaps with sheet metal brackets that are pinned to the bag wall and screwed or bolted to the studs. Fine sand is not the best for building because it shifts so easily, but as long as everything is vertical and connected to the studs and top plate sufficiently, and you use barbed wire between the courses of bags, it should be OK. If you want to be totally confident in the wall system, you might put buttresses in between the studs at 5' intervals and go up 6 - 8' feet with them.

Q: I will be attaching a four wall earthbag addition to our single wide mobile home, and I was wondering if the earthbag wall that will be up against the mobile home exterior should have some kind of vapor barrier, or should I remove the vinyl siding, or provide a small gap between walls, leave siding, etc.? I was hoping to leave the siding on, constructing the earthbag addition and then wrapping the entire home addition and all with white oak that I can get extremely cheap, plus it will have a cabin look/uniformity when complete. I do realize that if I do this there will still be an entire wall of vinyl siding behind the earthbags, but I was hoping there was a way to do this with out it being an issue. If it is possible to wrap the house in vertical white oak I was thinking to set wood strips every foot or so in the earthbags to attach the oak, but would I need to wrap the bags in Tyvek or something first?

A: I am generally a fan of leaving walls as breathable as possible, so that if moisture ever manages to enter, it has a chance to leave. Moisture barriers obviously stop this from happening, at least on the side where it is. The existing vinyl siding is waterproof, so there is need to protect it from adjacent bags. I think that your plan to attach stringers for mounting your oak siding is good, and this will also provide an air gap to allow transpiration in case condensation happens to form within the wall system. I see no need for a moisture or vapor barrier.

Earthbag Sauna and Kiva

Q: We are planning our retreat and your construction seemed less labor intensive and quicker than many of the others. We are considering bags of pumice for our massage rooms(2), sauna(1) and a cylindrical kiva. (The land we are looking at has an abundance) The buildings will be oriented to North, South, East and West with radiant heat, hopefully heated by the wood stove in the sauna. The massage rooms and sauna will be domes. The two massage room domes will be 12' in dia and the sauna will be 15' in dia.. We would like to earth berm the North side up about 4'. From our discussion this doesn't seem to be a problem. Is there anything we should be aware of? ( Excess moisture in the sauna?? )

A: As you know I bermed our earthbag buildings with over four feet of soil, and that is working out well. I used a couple layers of plastic sheeting outside the bags where I did the berming to keep moisture from seeping through. As for the interior of the sauna, I might suggest that you use a standard concrete stucco or cedar wood rather than the papercrete that I used, because the warm, moist environment would be perfect for harboring mold in papercrete.

Q: The second question is regarding the kiva type structure. We plan to have it completely buried, except venting. It will also be 15' in dia. and have an underground hallway leading to it. Will the bags support the weight of being under 1'-3' of earth? We were considering using a flat roof system, much like a mine shaft. Any suggestions here?

A: I presume you are thinking of of using very heavy timbers and decking to support the earthen roof, and resting these timbers on the cylindrical earthbag structure. I would think that the earthbags could support all of that weight without any problems; the compressive strength of most earthen materials is enormous.

Papercrete/Steel Quonset Vault/Earthbag

Q: Isn't a steel quonset hut redundant? Why not form the earthbags like Nader Khalili intended as an arch or dome supporting itself?

A: Good question. Actually, a large vaulted structure is extremely difficult, if not impossible, to create using earthbags. Nadir Khalili has never attempted it. The largest earthbag vault that I know of is one that I built as part of my house, as a mudroom entry, that spans eight feet at the base. The walls of this are some 30 inches wide in order to provide sufficient buttressing for the vault.

What Nader has done with his vaulted structures is provide the vertical, buttressed side walls using his Superadobe technique, and then created the vaulted roof with a form covered by stabilized adobe, I believe. This vault ends up being only about 6 to 8 inches thick. Also, his vaults span about 12 feet at the most...my workshop spans about 16 feet. Using the steel quonset as a permanent form/interior finish seems like the simplest, and sturdiest way to achieve what I want.

Q: Can another material be used for the vault form such as plywood?

A: I imagine that plywood would work to create a form also. I have made smaller arch forms by cutting the shape out of plywood and then attaching 2X4 (or greater) to the plywood, following the shape. The thing is, though, that wood means trees being cut, whereas much of the steel used these days is recycled. The Steen's light straw/clay blocks may be the most ecological solution to making vaults.

Q: Would like the source of the supplier of the metal quonset hut that Kelly is earthbagging and papercreting. Also wondering what the size of his hut (length, width and height). What is the gauge of the metal hut?

A: I bought the quonset kit (minus the end walls) from U. S. Buildings (www.us-buildings.com ) out of Florida. The nominal size is 16 feet wide by 34 feet long, and the height of the metal part is 11.5 feet (although I raised it to about 15 feet with the bag stem walls). The steel they used is relatively thin, but plenty strong once the shaped sections are bolted together. They probably say at their website what gauge steel it is. I paid $1,900 for this, delivered to Colorado, with two buckets of stainless bolts to assemble it.

Q: I noticed your Quonset hut project. I've been looking to do something similar. I intend to buy a modern steel span (www.americandurospan.com) and earth berm it. It'll be larger than the one you have and mostly arch with only a few feet of vertical wall. I've been looking at different passive solar designs, and I think I'll be okay with a solid concrete and rock pad on the bottom. I'm trying to figure out the exterior though. The shell will have to be strong, insulated, and water resistant, as I'll be living in a temperate rain forest. I've been thinking of 2" or so of ferro-cement for the shell exterior, with papercrete or light weight concrete for outer insulation. Do you think papercrete would have moisture issues? I'm worried about the expansion of the outer material since the rest of the building will be high density steel and ferro-cement, it seems like they might separate or have some other stress issues. I've also found little information on the strength of papercrete other than the demonstration on your site I'll be berming on both sides and one end, so it has to be very strong.

A: In looking at the americandurospan site, their quonsets seem to be very similar to what I used ( us-buildings.com ) . I would think you want to use the S-series true vaulted shape, as it is much stronger for supporting any kind of weight on top. By berming the sides you can add quite a bit of weight over the arch without distorting the shape. Mine is supporting about 50 lbs per sq. ft. I expect. There are definitely issues with moisture and papercrete...it has to be able to dry out if it gets wet, so sandwiching it in between rather impermeable layers (steel and concrete) might not be a good idea. Papercrete does not expand when it gets wet, surprisingly; it is quite dimensionally stable. It would loose its ability to insulate and can harbor molds if it stays wet and warm for too long. If your climate is sufficiently temperate, you might be quite comfortable by covering the entire vault with a layer of earth and be done with it. Plant flowers up there!

Q: How are you constructing the foundation for buildings like your carriage house?

A: Both my dome house and the Carriage House have earthbag foundations, that is the earthbag walls provide their own foundation. This may sound strange, but there is no other foundation for these buildings, and this is the way that Nadir Khalili has built many of his earthbag structures. This has worked well for me in my location, but I should add that I am building directly on pure sand in the desert southwest. In areas with heavier soils or more precipitation, I would recommend starting the earthbag walls on rubble trench foundations to avoid any moisture penetrating the walls or frost upheaval. Earthbag structures do not need a solid monolithic foundation for proper support.

Q: Rubble trench with or without bond beam? could you give me more information about the wall assembly of the steel quonset carriage house (what is the composition and what is the construction process for the walls?) It looks BEAUTIFUL, especially the marriage and separation of the materials.

A: For an earthbag wall, the rubble trench does not need a bond beam...for something like strawbale, this would probably be a good idea. The earthbag stem wall of my carriage house is made with two parallel columns of earthbags that are tied to each other by periodic straps of barbed wire, so that they cannot separate. A wooden top plate (wide enough to set the steel quonset panels on solidly) is then pinned to the stemwall with long sections of rebar. Before this plate is set in place, steel angle brackets are mounted at intervals to match the pattern of the quonset ribs, with the bracket hooking under the plate when it is in place on the wall. This allows the quonset to be firmly bolted to the plate, making the whole assembly connected. Then I stacked the earthbags over the quonset vault, being careful to tie the inside firmly with either cable or wooden joists at the spring line (the point where the vault starts to curve inward) before placing much weight up on the vault. At this same place, on the outside, some kind of retainer (I used lengths of 2X6 lumber) needs to be attached outside the bags and bolted through to the steel to keep the vertical column of bags from being forced outward and collapsing. If you look carefully at some of the images above this should make more sense. Once the bags were all stacked, I stretched 2" chicken wire over the whole thing before plastering it with the papercrete (could use stucco). The result of all of this an extremely monolithic structure that should last a very long time and is well insulated (I filled the earthbags with crushed volcanic rock, but they could be filled with styrofoam, perlite, or some other stable, light, insulating material).

Q: I looked at your quonset hut building; it was quite interesting. Do you remember what the manufacturer's rating for snow load was? I ask because that structure was obviously strong enough to cover completely with earthbags, and I'd like to figure out the amount/weight of
the rebar I'd need to match that rating.

A: According to the specs from the manufacturer, the building was designed for at least 50 PSF live load on the roof, 62 PSF ground snow load, 90 MPH wind velocity, and seismic zone 4. I should add that I reinforced the loading capacity substantially by firmly attaching wooden joists every 2 feet on the inside at the spring line of the vault. This could also be accomplished with tension cables across the inside.

Q: In your steel-shelled shop, how did you attach the joists (for the loft) to the steel shell? I have one of the peaked-style buildings (16' wide, 11'6" high at the peak) and I'd like to build some overhead storage.

A: I fabricated steel brackets that are bolted to the joists and also to the steel shell, using the same bolts that are used to attach the sections to each other.

Q: I assume the bracket just goes under a second nut on the end of the section bolt, and the joists are cut to clear the bolt ends.

A: You are basically are correct, except that I didn't use a second nut, I removed the original one and bolted the bracket tightly against the steel rib of the shell, and left enough clearance when cutting the joists to fit with the bolts protruding.

Q: I am considering buying property that would accommodate an airplane, i.e. private strip, plus a large hanger. My best idea has been to buy a ranch with a large barn, but my preference is to build something myself out of natural materials. I think that there should be a relatively simple way to get a round structure with high walls (possibly rammed earth), and then use steel roof framing over the top, utilizing it's lightness and strength. Will also be looking into the possibilities of an earthen base, and then creating an inflatable roof which is then sprayed lightly and repeatedly with concrete (or some other material). I believe that this is already being done, and seems to eliminate many of the complexities of erecting a large dome.

A: I recently constructed a building on my property that I call my Carriage House, that is a hybrid design that could be modified to be large enough for an aircraft hanger. It is basically using a steel quonset shell as a form to make an earthbag/papercrete vault. These prefabricated steel structures come in all sizes, and are actually used as hangers. They are relatively inexpensive and quite adaptable to accommodate various design modes. They can also be bermed substantially, or even buried completely if backfilled properly. You might think that steel is not all that "natural" but in my opinion this is a reasonable option because most steel is actually recycled, and the vaulted quonset shape spans large distances with minimal material.

Q: Has this been considered: build the typical quonset hut via US Steel or others with an insulated concrete slab that has the radiant heat tube for various methods of heating. Cover the quonset with straw bales. Cover the straw bales with a reinforcement material. Spray the reinforcement material with shot-crete. Paint shot-crete with an Elastomeric paint fitting to your environment. Build end walls with straw-bales and repeat the process of reinforcement and shot-crete. Your thoughts please!

A: The trouble with using straw this way to cover a quonset is keeping it dry so it won't rot. The steel shell will keep interior moisture-laden air from condensing in the straw, but while shotcrete and paint can do a good job of repelling moisture, it is not guaranteed. Any slight crack in the cement/paint layer can admit water, which would then not be able to evaporate and would fester in there forever; this sounds like a maintenance nightmare to me. A better solution, if you wanted to use straw this way, might be to attach wood stringers to the straw, and then use some other roofing material, such as metal, over this in such a way that the straw can still breath. I see no problem with using straw for end walls, as this is similar to any other strawbale building. Another approach might be to use an insulation material that is not vulnerable to moisture damage, such as the volcanic rock that I used, or even recycled styrofoam, packed into earthbags and then plastered over.

Q: I ran across your quonset hut experimental building and was very interested because it is similar to what we have planned. We have a 45x40 quonset hut 17' tall (unerected). We plan to use recycled styrofoam (from docks) cut into blocks and pinned together with rebar and stacked against the sides, then coat the whole thing with cement. If you have never seen the styrofoam they use to hold up docks it is sheets of styrofoam (the kind made of a lot of little beads)4 or 5 feet wide by 8 to 10 feet long (or cut to size). Each sheet is 10" to 12" thick. Two of these sheets are stacked and glued together to make a 20" to 24" thickness. When they eventually become water-logged they are pulled out and replaced with new. The old is then taken to landfills. Not an environmentally friendly solution. They eventually dry out and then are very light weight. It is very strong and super insulating. What do you think?

A: I think this sounds like an excellent idea...a great way to recycle waste styrofoam!

Q and A: We are from Hawaii and are currently working on developing an art center up on the North Shore of Oahu, where we recently purchased some land. We are interested in your use of steel arch buildings covered w/ papercrete, and would especially like to find out more about how you covered the structure. Did you spray it on like gunnite, w/ a wire mesh skin?

The papercrete plaster was applied by hand, with a 2" chicken wire mesh embedded. But the bulk of the insulation over the vault was created with earthbags filled with crushed volcanic rock.

What about other lightweight concretes, like those using foam and/or other lightweight aggregates?

There are other lightweight concrete formulae that could work.

I would like to incorporate about 4 of these structures w/ other freeform covered walkways, etc. to connect them together. These I envision also made out of some kind of lightweight concrete that we can make into interesting shapes. What would you suggest?

All of this sounds possible...it depends on the specific design what might be best.

Was permitting a problem for you?

No...we live in a county where this is not an issue.

We are in a rather rainy area of Oahu, and from the little I've read, it seems that papercrete absorbs a lot of water. If this is true, then it might not be the best material for us.

It is true that PC does absorb water, and for this reason might not be your best solution.

Also, as we are planning to build quite a bit, we need to find something that is relatively inexpensive but durable.

PC is inexpensive and quite durable from my experience, but probably not as durable as some of the mineral-based lightweight materials.

It is also important that we can mix the cement in large quantities and spraying seems to be the fastest and easiest way to cover 4 or 5 of these (20' high x 30'wide x 25' long)--have you ever sprayed any lightweight concrete?

PC has been successfully sprayed, as has some of the finer aggregate mixes I suspect, although I don't have personal experience with this.

Or is it rather quick and easy to trowel on?

Like I mentioned earlier, we applied the PC just as a plaster over the earthbags, so we simply bucketed the slurry to where it was needed and smoothed it out by hand.

Was weight a problem for you (i.e. the weight of the earthbags along w/ the papercrete--what was the load bearing capacity of your steel arch building?).

Yes, this is a major consideration, and one that the manufactures of the steel buildings will warn you about. The buildings are designed for a certain snow or wind load, and they don't want you to exceed this. What I did to counter the additional weight was reinforce the structure internally with either cable or joists installed at the spring line. I have some plans for sale that detail these attachments: http://www.dreamgreenhomes.com/plans/carriagehouse.htm

Q: I am a student of environmental architecture at the Centre for Alternative Technology in Wales. I am writing a paper on the prospects of earthbag architecture in the mainstream. I am really impressed by your Carriage house design. Could you please estimate the total cost, man hours and dimensions of the carriage house?

A: I appreciate your interest in the Carriage House design. I have actually drawn it out, so you can see for yourself what the dimensions are at http://www.dreamgreenhomes.com/plans/carriagehouse.htm

As far as cost and man hours, I will have to estimate, since I didn't keep accurate records of these. I believe that the cost was under $5,000 U.S., with the steel building being about $1900 (delivered with bolts, but no end walls). Much of the material I used to build it was recycled, including the bags of scoria (recycled from the building shown at http://www.greenhomebuilding.com/earthbag.htm#Matts ), the framing wood for the end walls (from a dumpster at a neighbor's building site), the cedar lap siding (remnants sold at discount), and the windows. Wood for the second floor joists and flooring were new. The cost of the papercrete was negligible. I did hire a couple of Mexican roofers to help put up most of the earthbags and papercrete on the vaulted portion, and some neighbors helped stack some of the bags and pour the concrete floor. I worked periodically on this building for about two years, whenever I had some extra time. A wild guess would be around 1,000 man hours.

Q: Can you provide approximate costs for building the carriage house?

A: I  can tell you that I spent about $5,000 to build mine, but I was lucky to get an exceptional deal on the metal vault, found recycled materials for most of the other components, and did most of the work myself. I am guessing, without actually costing the parts and labor, that it could be built for around $20,000.

Q: I was intrigued by your quonset type garage on a raised earthbag foundation. I have such a structure, 20 x 30 which is not yet set up because I've balked at the cost of the concrete foundation. How was the 2x10 board fastened to the earthbags. I want to set mine right on the ground and find some means of holding it together rather than grouting it into a concrete trench on a 20x30 slab. Any advise would be appreciated. Wind is a concern here in North Dakota.

A: There is a cross section diagram of how my Carriage House was assembled at http://dreamgreenhomes.com/plans/carriagehouse.htm  . It might be a little hard to see. Basically, the steel quonset is attached to the 2X10 with a heavy L bracket that goes under the wood and is screwed into the wood and bolted to the steel. The board is then pinned to the earthbag stemwall with 5/8" rebar pins going all the way to the ground at about 4 ft. intervals. Then, the whole thing becomes monolithic with the stucco netting and papercrete or stucco plaster on the outside over all of the earthbags. I would suggest that you raise the 2X10 up off the ground a foot or so on earthbags, so that it is away from the dirt and so that you have some hefty weight to counter those North Dakota winds.

Q: I'm considering using a quonset style steel roof (1/3 Arc 28' span) on a 8' high poured foundation. Using the roof as a braced form for a reinforced concrete shell 3"thick, leaving it in place as part of the ceiling. Any thoughts?

A: I have two comments about what you are proposing:

1) It will be essential that the base of the quonset, at the level of the concrete foundation, be substantially braced with either cables or joists that are adequately connected the the steel structure. This is to withstand the outward pressure created by all that weight from splaying your foundation. This is true even without the additional concrete.

2) A concrete shell poured over the steel will not provide any real insulation from heat and cold, so unless you live in a very temperate climate, the space will not be comfortable for occupancy much of the time, without further insulation. In fact I don't really see any advantage to pouring such a concrete cap, since the steel shell itself is plenty strong.

Q: I am interested in using papercrete to insulate the inside of a arched metal quonset style building. It sounds like spraying the material on is possible. Has anyone tried using a drywall texture gun to spray it? The building will be used as a shop and storage area for equipment and vehicles, and I don't want everything covered in rust. Would something like gypcrete work better in this type of application, or is it a sponge too?

A: People have successfully sprayed papercrete, but it can be difficult; the pulp tends to clog nozzles very easily. I don't know about using a drywall texture gun. One type of sprayer that would likely work was designed for ferrocement applications. It has an open hopper that air is forced through to spray the material. This has been used for various earthen materials as well. You can see these at http://ferrocement.net/cgi-bin/shop/i-shop.cgi  under "sprayer".

A larger issue might be getting the papercrete to stick to the smooth metal. It might work to spray a light coating of something that has better adherence on first to give the papercrete some "tooth" to hold onto. Or you could somehow fasten stucco netting to the metal shell using the existing bolts.

Gypcrete might also work in this application, but it won't give you much insulation. I doubt that either would have problems with moisture once they are cured. The papercrete will take much longer to cure, and the building will have to be left as open as possible for this to happen; during this time it will be very humid in there.

A whole other approach to insulating your quonset would be like I did for my Carriage House. See this page  or   http://dreamgreenhomes.com/plans/carriagehouse.htm for a description of this.

Q: I am strongly considering an interior insulated quonset hut for living space. Would there be any condensation concern from spraying icynene on the inside? (northern Alabama climate) I'm also especially curious if there is a spray on fireproofing for this insulation that could also serve as the finished surface .... something light enough to be sprayed directly to the foam without any additional support besides the steel-icynene bond?

A: I wouldn't expect there to be any problem with condensation with what you describe. It is fairly common to spray metal buildings with interior foam insulation. As for the fire proofing, I don't have any information about this. You might ask some of the specialists who do this sort of work if they know.

Q: My husband Mike and I are planning to erect a steel quonset style building on our land near Westcliffe, and insulating it as you did the carriage house. Have you seen any indications of degradation of the scoria bags or papercrete in the years since completion? I want to go in to this with my eyes open, and attempt to mitigate any future issues right off the bat.

A: I have been very pleased with how this hybrid steel quonset/earthbag/papercrete building has worked out over the last few years. The only degradation that I have noticed is a slight flaking of the very exterior surface of the papercrete. At some point it may be necessary to put a more durable coat of stucco over it...or this could have been done when I originally constructed it.

C: I've been working on a vault design that uses an internal frame for support - this frame consists of left-over grain bin parts and some reclaimed lumber. I had this idea of covering the external walls/roof with canvas or yurt vinyl material. 1" reclaimed pvc conduit pipes would be fastened to the underside of the canvas or vinyl horizontally to keep the covering off the plastered walls so the walls can breathe. In good weather the covering can be lifted off the sides of the vault to offer patio shade and shelter on either side of the vault. I ran into this site that constructs an A-frame style vault home that is used in South Africa. www.myabod.com I liked the shape of these buildings but it is uninsulated. What if  an A-bod could be use as a frame to place earth bags filled with scoria or perlite up the sides (like your Quonset hut in the carriage house)? For places that receive much annual rain and snow fall the Gothic arch shape would shed much better - a canvas or vinyl covering would give added protection and the A-bod frames would be very affordable ( starting at $1500). I think that an A-bod/earth bag home would make great little Carriage Houses. They make a 16'x20' model - with the sleeping loft this would make a spacious "Tiny home".

Q: I live in central Arkansas...cool winters...hot and humid summers. I am thinking of building a home using a quonset covered with garbage bags filled with shredded paper and then a layer of soil. Do you think it would work?

A: I am afraid that the soil would compact the paper to the point that it wouldn't make very good insulation...and also if the bags leaked some and the paper got wet, it would eventually decompose and really be no good for insulation. I would suggest that you use something a little more durable to insulate the quonset in this circumstance.

Q: I got my idea from looking at the carriage house on the web site. From the picture it looked like smaller earthbags were used on the top.  Do you think a small shell will hold full sized bags over the arc? I also noted that ya'll had done some wind testing on the earthbag structures.  I'd like your opinion on using my proposed structure (steel shell, surrounded by earth bags) as an above ground  "storm cellar". From what I've seen of storm cellars here in tornado alley, they are damp, dark, and basically unused for anything except an emergency.  I'm hoping we can find a reasonable, inexpensive compromise that allows for everyday use, as well as storm protection.

A: Actually, on the Carriage House I used the same size bags throughout, but laid them horizontally, so as they were placed over the steel vault, the apparent thickness decreased. If I had placed them radially as I went up, the thickness would have remained more constant, except that gravity tends to squash the bags down in this case. I do think that a smaller vaulted structure would also hold the bags, but it is important to weight these symmetrically as they are placed, alternating sides as you go up, so that the whole process is in balance. Also, it is important to tie the vault periodically with cable or wood joists (as I did with the Carriage House) to assure that it doesn't splay out with the weight...although this may not be as important with a smaller vault.

I am not aware of any specific wind load tests done on earthbag structures; I think this has been just anecdotal. I believe that the commercial steel vaults have been tested with wind loads and have performed well. Adding earthbags as a surround on the structure should increase the resistance to wind loads I would think...but I am not an engineer. I think that either the bermed steel vaulted structures or earthbag dome structures have much to offer in above ground storm shelters. See http://dreamgreenhomes.com/styles/rounded/domes.htm  for some of our dome designs.

Tire/Strawbale/Earthbag

Q : We are working on a hybrid of ideas for a building ... a house with one back room 16' in diameter circle two stories tall, the first level back wall built mostly into the hillside, so we figure to ram earth tires till grade or just above, then earthbag, superadobe to reach proper levels to put strawbale on top. My question arises with the bond beam between the first and second floor and the roof; it is a load-bearing bale house ... ideas we have: 1. poured concrete bond beam (lots of money and not that ecological by our terms, 2. superadobe earthbag (strong enough?) 3. a re-salvaged welded metal I beam (too much?) any thoughts also in the back wall we wish to build a root cellar into the wall tries, ok ?

A : It sounds like you have an interesting project. I have several thoughts about what you describe. First, I wonder why bother with pounding all of those tires when earthbags would do the same job much easier? You can bury an earthbag wall just as well as a tire wall, especially when the wall is curved, as yours will be. You just need to bring the wall up high enough to be above grade to begin your strawbales. In this instance, I don't think there is a need for a bond beam...unless you are dealing with code officials who might have other ideas. The barbed wire between courses of bags acts much the same as a bond beam. I did something similar in my house, where the first floor is completely bermed on the north side; I simply made a skirt of 2 layers of 6 mil polypropylene draped over the back of the bags before backfilling. You might want to insulate with blue board or something back there, if you don't fill the bags with crushed volcanic rock as I did.

To make an entrance into the pantry, using bags would be easier than tires because you can easily make an arch with the bags over the entrance, and making half bags is probably easier than making wooden fill blocks for half tires. For the second floor, you could start stacking the bales right on the earthbags once you have an even bag surface above the joists. If it were me, I'd just continue the wall with bags, since it might be easier than making a circle with bales, but I'm partial to that technology. You will want some sort of bond beam at the top of the bale wall, which is usually done with wood planks, but isn't so easy with a circular building. Probably a poured beam with rebar and cement would be the easiest. I wouldn't rely on superadobe for a bond beam in this application. Salvaged metal might work, but it would be hard to get enough surface to not sink into the bales. Again, if you went the whole way with bags, you wouldn't need the bond beam.

Q : I have yet another question, and I know you suggest the earth bags all the way up but if I did stack bales on top of the bags would the bags act to wick up water into the bales? Also a man out in New Mexico was using recycled latex paint mixed with organic blown insulation to a paste consistency and was using this painted on a bale roof and till this point no problem... I want to say at least one year if not three. He actually mudded it like it was mortar. What are your thoughts on this as waterproofing if any? And also there is an earthbag house in Colorado they call the beehive that is having problems with the earthbags in the foundation leaking water. You have no such problem because of the liner eh?

A : Earthbags used as a foundation for strawbales are usually filled with gravel, which does not wick water. Other earthen materials might wick some water, but you can stop this by simply putting a moisture barrier between the bags and the bales. The problem with waterproofing strawbales is that it stops them from breathing, which is generally essential to assure that the bales stay dry. Any moisture barrier runs the risk of creating a surface where moisture can condense from the inside. Using bales as a roof is very difficult for this reason.

I don't believe I am familiar with this beehive house. I haven't had problems with leaks in mine. The only place I used the plastic liner was where I bermed soil up against the bags, otherwise my house is completely breathable. With the papercrete plaster, the water never has a chance to find its way through the bags, at least in my climate. Without knowing the specifics of the problem you spoke of, I wouldn't know what to say about it.

Q : I was also pleased to hear about your passive solar performance. I would like to have enough windows for light and passive solar, but blending in to my environment is important to me (one reason for my berming low into a hill), and huge banks of windows are hard to do that with. I have seen various"formulas" for determining the proper amount of window square footage for passive solar, ranging from 10% (of floor square footage) to 20% (and the 40% as you mention). Do you have any idea what you ended up with?

A : A quick guess is about 30%. The colder the climate, the more you need.

Q : Also, I was intrigued by your scoria there again. The naturalhouse.com guy isn't too hot about strawbale homes, claiming they lack the thermal mass for effective passive solar. You talk about your scoria having insulation qualities comparable to strawbale, but you obviously have sufficient thermal mass as well. Maybe it is that air space in scoria again--good for the insulation, but still plenty of igneous rock mass for thermal mass.

A : I wouldn't expect much thermal mass from the scoria. My mass is in the flagstone and adobe floor, and in portions of the house where the earthbags were filled with the sand. Whenever I could isolate these bags of sand in the walls, I did so. For instance, the first two or three feet of the bermed wall is made with bags of sand, and then this is insulated with more scoria on the outside, before it was backfilled. Also the entire landing from the main entrance to the house is created with bags of sand. Most of the internal papercrete plaster has a lot of sand in it also.

Q: I'm looking at buying a half-built earthship and have a couple questions. The site has 3 U's with about 5 ft. of tires, pounded with earth. Could you finish the rest with strawbale, 3-4 bales of straw?

A: You could certainly do this as long as the strawbales are completely above grade (not bermed). Tires have been used many times as a foundation for strawbale structures.

We're thinking about pounding rebar in and putting strawbales over the rebar. Would that be enough to support the roof or would you also want to add corner posts.

Pinning the bales with rebar is a good idea. Strawbales can be used as load-bearing walls, but this takes some care to allow them to compress some before plastering (or pre-compressing them with tensioned straps.)

Also the U's are not very curved so I'm a little concerned about the support of the berm on the north wall. Could this be solved by not building up the north berm as much?

Yes, although it doesn't take much of a curve of the tires to be very stable. If you decide to complete the walls with strawbales, then you wouldn't be berming up above them anyway.

If we increased the curve on the next couple of tire courses would that help?

I suggest that you keep the curve of the wall consistent and keep the walls vertical.

Strawbale/Cordwood/Earthbag

Q: I plan on building a hybrid building (straw, earthbag and cordwood). This building will consist of an inner circular tower that will be 2 stories and capped by an earthen roof. This tower will be built using cordwood construction. The outer circle will serve as the first floor and be a post and beam framework with straw bale infill; this will also be capped with an earthen roof. My question is, is it safe to lay down a bed of sand (6-12 inches deep) and lay down earthbags as starter walls for the inner and outer circles? And what is the best way to fasten the posts to the earthbags?

A: You didn't say where you are building, what the climate is like, and what the natural soil is at the site. I built my earthbag house on a huge sand dune, with no foundation other than the earthbags themselves. Sand drains nicely and compacts instantly, both of which are good traits for building upon. It also can shift and blow and move around with currents of water, so it needs to be contained somehow. The big question is frost upheaval with foundations, since you don't want the structure moving up and down if the ground under it freezes. My house is built upon several yards of sand which drains well enough that frost upheaval has not been a problem. If, on the other hand, the soil you put the sand over holds water and the frost depth in the winter goes below your layer of sand, then upheaval could be a problem. One way to avoid this is to make a rubble trench foundation down to the frost depth, and then begin building with earthbags on this, filling the first course or so with gravel, so there is no way for water to wick up into the strawbales. The inner tower could be built right on the sand, since there would be no danger of freezing inside the outer perimeter.

Q: I am planning on building a cordwood and strawbale home using an earth bag foundation. I helped my neighbors down the road build their strawbale home on a earthbag foundation set on a pad of sand. My two big questions are how would I anchor the post to my building to the bags so that the house isn't lifted up by our strong winds?

A: I suggest that you not try to anchor the posts to the earthbags, but anchor them to conventional concrete piers instead, and then create the rest of the foundation as an infill to this. That way there is no question about settling or uplifting.

Q: How important is it to cover the bags with mortar? I realize the importance of covering the bags (polypro) to prevent ultraviolet deterioration, however in my plans the outside will be insulated with foam boards. Keep in mind that the foundation I'm attempting is simply a 16 by 18 foot rectangle three courses high. I will cover the insulation with a lime plaster. My big question is if by not covering the bags with plaster am I sacrificing strength?

A: The strength of the earthbags as a foundation under compression does not rely on the plaster, so as long as the bags are ultimately covered to protect them from the sunlight, this should be fine. It may be necessary to temporarily cover them with a tarp until they get covered, though.

Q: Could you use Kelly's double earthbag wall ideas to build a cordwood home for the foundation and for the earthsheltered parts of the structure - have the front (south facing) side of the home bermed two feet. My thinking is that the cordwood makes a great bond beam for the above ground sections of wall. You could even put a buried earthbag dome pantry behind the north end of the house ( like the one in Kelly's home). This would save on cement ( which contributes to greenhouse gases)- Insulation on the north side of the bermed wall would add greatly to the thermal mass.

A: There is no reason why this concept shouldn't work. Many strawbale homes have been built recently using earthbag foundations. They are a natural for situations with earth contact, whether as a foundation or as a bermed wall. There would probably be no advantage to the double wall concept, though, since an insulated single wall should work just fine. I would not rely on cordwood masonry to create a "bond beam"; a better approach would be to actually pour a concrete bond beam on top of the earthbags, and then start laying the courses of cordwood above this. If you fill the bags with crushed volcanic rock, as I did, you would not be adding much mass, but this is where the double-bag wall idea can excel, if the inside is soil and the outside is insulating.

Q: I am wanting to build a home on our family farm. I am still going back and forth on earthbag vs. cordwood. We have all the wood we need, but it seems like earth bag might go faster or be less expensive. I like the look of cordwood better, I am just unsure.

A: (Owen Geiger) I would say earthbag and cordwood would take about the same amount of time. Earthbag may be a little faster, but not much. It would partly depend on how accessible the wood is. The cost would be nearly identical. Other factors would be more important: fire and insect resistance, insulation value, and so on. Cordwood is prone to air leaks, so is not the best choice in very cold climates. One option that would be real attractive is combine the two -- some parts could be earthbag, some cordwood. Imagine cordwood around doors, etc. as an accent.

Concrete Block/Strawbale or Earthbag

Q: I want to insulate the exterior of an old cinder block garage that's now a living space (too narrow for interior insulation): straw? earthbag? other? Also needs to be something a 62 y.o. woman can handle!

A: Both strawbales and earthbags filled with insulating material (crushed volcanic rock, rice hulls, perlite) would conceivably do the job for you. Strawbales would need to be set on  their own foundation; earthbags could perhaps be put on the ground if the fill is not vulnerable to rot. Then either of these would also need to be protected by an overhanging roof, and the details around doors and windows can be tricky. A simpler approach might be use conventional rigid insulation (like blueboard) attached to the wall and then protected with a stucco or something.

Plywood/Strawbale/Earthbag

Q: I'm thinking of building a 30' earthbag yurt style home in northern Maine, with a plywood roof and then covering the whole thing with 6 mil plastic and straw bale on top for insulation. You talk of the walls being able to breath, what do you think?

A: In general, what you describe sounds like a reasonable plan. The strawbale roof should give you plenty of insulation up there, but you will need to keep the straw dry for it to be effective and last over time. Also, in your climate you will want the walls to be insulated, so that may affect what you decide to fill the bags with. I filled mine with a crushed volcanic rock, but other alternatives might be perlite or rice hulls...or you can fill the bags with your local soil and then insulate the outside of the walls some other way.

Q: I know that the straw will break down over time and I'm willing to live with that. My idea was to cover the whole house with a 6 mil plastic roof and earth bags and then with straw bales for insulation. The idea came from the old Indian earth lodge's and from trying to keep costs down. Can you give me any more options other then plaster for covering the earth bags if I were to use conventional insulation?

A: My suggestion that you keep the straw dry is partly for your own comfort, in addition to the longevity of the roof...wet straw will not provide much insulation. You might consider layering the roof with plastic-straw-plastic-straw to maintain some real insulation. Another option for an insulated earthbag wall is to actually create a double wall, with a space between the two columns of bags, which can either be left as an air void, or filled with some other insulative material, such as straw, cellulose, vermiculite, wool, cotton, rice hulls, etc.

Timber/Strawbale/Earthbag

Q: I am considering building a timber frame house with straw bale wrap. I've been thinking of a earthbag vault roof. I like your idea of the light weight volcanic rock filling. My question is do you know any source(s) for this type of roof design and do you have any personal input in this design.

A: In general, your design concept sounds nice, but I would caution you against the use of earthbags for a vault...they do not perform well in this configuration. I made an 8 ft. span vault with earthbags filled with scoria, and I feel that this was pushing the limit of their capacity. A denser, more solid material will perform better in spanning larger distances with a vault.

Q: What would you recommend for the arch material? I prefer a self-supporting roof. Any ideas? Do you think cob would work or am I going to have to go to the (non-green) light weight concrete, maybe pumicecrete? I know the Auroville Earth Institue builds this type of roof using adobe type bricks.

A: Nader Khalili made houses using earthbags up to the roof level, and then switching to adobe blocks to complete vaulted roofs over them; I think the vaults spanned about 16' at the most. Cob could probably be used also, but it may require a form under it, because the cob is moist when applied and can slump with gravity. Then there is the whole question of insulating the roof and how to accomplish this. Poured lightweight concrete with some steel reinforcing does have some advantages.

Q: We live in a Pan Abode log house. I have been having a great deal of trouble finding out how to improve its acoustic and insulative aspects, and its rain resistance (which is lousy). The company itself will naturally swear that log houses are fine in all aspects, but they aren't, at least not in this climate of Nova Scotia. I know we will need much wider roof overhangs. My quandary is, how to effectively apply bales, or even earth bags (which may be the better choice because of wind-driven rain here) to the exterior, without eventually running into trouble with moisture infiltrating into the bales from the interior of the house, through the logs, which are only 3 inches thick (I understand what is needed for plastering the exterior). I have read some of your replies about coating the side of a bale that is in contact with siding of various homes, but my worry is about this coating, that would be against the exterior log wall surface, being able to dry out properly after installation. Would it work to give a coat of lime/clay plaster to the exterior of the log walls, let it dry, and then place the bales against that surface? Would moisture transference from interior to exterior still be able to occur? If I were to end up using earth bags, which I prefer to avoid because they are so heavy, there is still the fact that the polypropylene is against the log walls and would likely interfere with moisture transference.  I want to maintain the internal acoustic properties that the logs have (not using insulation on the interior) because live music played inside is amazing.

A: (Owen Geiger) I recommend using earthbags for rainy/humid regions such as yours.  Sooner or later water will find a way through and cause problems with straw.

Consider using a lightweight fill material such as scoria, pumice, vermiculite, etc.  There's no need to do lots of laborious tamping this way.  In other words you're adding insulation, not a load bearing structure.  It can go on the exterior so the interior living space is unaffected.  You'll need a foundation under the earthbags.  Consider a rubble trench.  Then simply tie the bags to nails on the logs.  Problem solved.

What about the fact that the polypropylene is against the log walls: won't it interfere with moisture
transference moving from the interior of the house through the logs?

I recommend good fans in the kitchen and baths that exhaust moist air to the exterior (not the attic).  Then you should be fine.

Stone/Adobe/Rammed Earth/Earthbag

Q: I am looking at some land in AZ with red clay-sand heavily embedded with rocks. Have you seen any examples of earthbag building where they use stone facing on the outer wall?

A: I love stonework and suggest that you utilize this wonderful resource to some extent. It tends to be very time consuming, so bear that in mind. You could certainly face an earthbag structure with stones, but my suggestion would be to do this more on the inside where you really need the thermal mass, and then fill the earthbags with scoria (crushed volcanic stone) for better insulation...especially in AZ.

Q: I propose to build my house in the following way: Foundation with stones; walls with earthbag construction (rectangular); roof by vaults of adobe blocks. One problem I may face in future is rains, the effect of which on the vaults is unknown to me. Since I need an inner open verandah (courtyard), a circular design is out of the question.

A: What you describe sounds quite possible to me. A stone foundation is good, and earthbag walls would work well. The walls have to be thick enough to buttress the vault  (to keep it from expanding outward), so be sure to get some engineering advice about this. Your concern about rain on the vault is real. An adobe vault must remain dry, or there is the possibility of collapse. Sometimes people use stabilized adobes for the roofs, which will tolerate some rain. Here are some photos of the building of an adobe vault:http://www.adobealliance.org/misc-photos/

Q: I have seen some rammed earth buildings and earthbag structures near me. Is their technique a combination of the two forms? Does using the rammed earth as a foundation and starting wall and then using earthbags for the dome and such make any sense?

A: Rammed earth and earthbags are really quite similar in many respects. The most common fill material for bags is a mix of moistened clay and sand, which is virtually the same as for rammed earth. Then both techniques tamp or ram this material to compact it into a solid block once it dries. The main difference is that while rammed earth uses durable and removable forms into which the soil is compacted, earthbags use the bag itself as the form, which is left in place.

I don't see much advantage to combining the two techniques, but if you do I would recommend starting with earthbags filled with gravel as a base or foundation, and then proceeding with rammed earth above...if you are making straight, vertical walls. Curved walls are much easier done with earthbags.

Papercrete/Earthbag

Q: I am thinking about taking Nader Khalili's course on super adobe roll (earthbag). How does papercrete do in wet climates(OR)?? Can papercrete be blown on to interior wall for extra insulation?? I' ve heard it is hard to get building permits for earthbag constructed dome homes?? Also, is it hard to get bank loans for earthbag dome??

A: Nader is the expert on Super Adobe, since he basically invented it. His workshops are good, but expensive. How papercrete does in a wet climate is somewhat unknown, but I would think it might need to be sealed to avoid moisture problems.

Yes papercrete can be blown on the interior, if you have appropriate equipment for this. It does increase insulation, but you generally want insulation on the outside. As for building permits and financing, this is variable. Nader has been working on the permit issue for many years, and might be able to advise you. We got a mortgage on our earthbag house, but it was with a rather enlightened local credit union. Good luck with your project.

Q: I'm involved with real estate and rentals homes. I have found in my experience the most bang for your bucks is to stop the transfer of air between interior/exterior with modern doors/windows and vapor barriers however you risk having unhealthy houses and mold. New house construction isn't much better and the quality of work fluctuates greatly from contractor to contractor. Therefore I knew for some time nobody has a better motive to build a quality house for me than myself. I see you have built an earthbag shelter covered with papercrete. Since your earthbags are encapsulated now and the rammed earth can't breath I would think your earth could dry out and fail compression (like they did in New Mexico and that village church in Mexico), but then again the papercrete should hold the structure, right? I also wondered why you didn't attempt to waterproof the papercrete?

A: I didn't use rammed earth in the bags...they are filled with crushed volcanic rock, and then covered with the papercrete, which is NOT sealed from moisture...in our climate it does not seem to be necessary.

Q: We were planning on building a house out of papercrete but with the moisture issue on contact with the ground is it possible to build the first floor out of earthbags, then the second level out of papercrete? That would solve the problem of papercrete no being strong enough too support 2 stories. If this is possible how would you install the floor joists on top of the earth bag wall and then the papercrete?

A: Yes, what you propose is entirely feasible. There are several ways of attaching floor joists to earthbag walls. One approach would be to create a reinforced concrete bond beam at the top of the earthbag wall and anchor the joists to embedded anchors. Or another approach would be to create an alternative bond beam with metal or wood plates in a manner similar to what is explained at http://earthbagbuilding.com/articles/bondbeam.htm. In either case I suggest that you continue up above the joists with a course or two of earthbags (possibly filled with gravel) so that the papercrete is not resting on wood.

Q: I am curious if you were to build the earthbag/papercrete home again, what might you do differently? Stabilize the scoria? Still use papercrete?

A: There is very little I would do differently really. I would not stabilize the scoria, as that would likely diminish its insulating value. I might not use the papercrete again, as it turned out to be not as durable as I hoped, especially in areas that were subject to direct weather. The folks who bought that house, at my suggestion, subsequently applied a standard stucco finish to the exterior. I wouldn't build an elliptical dome again; better to keep the shape circular.

You said you advised the new owners to use standard stucco. I was under the impression that was not a good idea due to breathability. True or false?

It's a compromise; ideally you want breathable walls, but these are difficult to attain in a dome without a solid roof to shed water. For awhile the papercrete provided breathable protection, and it absorbed most of the moisture and kept it from penetrating the rest of the wall, but it didn't hold up well enough. The interior remained breathable however, with its papercrete and lime plaster.

Container/Earthbag

Q: Do you know of any projects using a shipping container as a frame/skeleton and then use earthbags for insulation, etc.?

A: I don't know of any such projects but have often thought that the two would combine fairly easily. The best approach would probably be to insulate the outside of the containers with earthbags filled with insulating material, such as crushed volcanic stone, rice hulls, or perlite.

Q: I really like the idea of using heavy strong steel boxes as the structural framework of a home, and it seems to me that containers would have one massive advantage - once they are in place and welded together (with plates welded over any gaps/joints, etc.), we would have a completely dried in and structurally sound box in which to work.  Anyway, as much as we like the utility of containers, they lack a lot when it comes to aesthetics.  We certainly do not want our house or even our outbuilding to look like containers when were done, so I'm wondering about using earthbags as an exterior.  It seems to me that the earthbags would nicely compensate for the lack of thermal mass in the containers (insulating ceramic paint (assuming it actually does work) can only do so much, while the containers would remove some concerns about structural rigidity with an earthbag structure (particularly in the mind of a building inspector).  Does this seem like a reasonable approach to you?

To consider the practicalities of this - how would you tie the earthbag exterior wall to the steel wall of the container?  I was thinking that it could be done via the barbed wire - either by welding the wire at points to the container walls so that your wire in between bag layers was tacked to the wall every so often, or by attaching something like D-rings to the container walls and running the wire between the layers of bags through that every so often.  Does that seem reasonable?  Do you think that exterior buttressing of those 40' long vertical walls would still be required?  Without buttressing, I'd be a bit concerned about the potential "pull" of the earthbag walls on the steel side walls of the container.  Also, I know that in brick veneer construction, there is nearly always a narrow air space between the framing sheathing and the brick - would something similar be required in this case, or could the earthbags be brought flush to the container sides?  On another front, do you think it would be possible to use earthbags to create a roof surface on top of the containers?  I'm picturing something very much like a typical adobe structure, with a parapet and a flat roof (well, apparently flat - it would naturally need a crown for water runoff).  What sort of material would you recommend as a finish for such a roof - concrete stucco?  Or would it be better to just pour a (relatively thin) concrete surface on the roof?

A: Much of what you say about containers is true. They do have to be insulated in order to be used for comfortable habitation. I have my doubts about the insulative paint being sufficient for the job, especially since I have read rather disparaging reports about the efficacy of this paint over time. Another approach to insulation (besides commercial foams and rigid boards) might be to use earthbags with an insulating material as fill. Rice hulls, crushed volcanic stone, perlite and vermiculite are possibilities for this.

Attaching the bag wall to the container should be fairly easy to do, either with what you suggest or possibly running loops of wire (it wouldn't have to be barbed) around one entire bag and through  an eye welded to the container. If this were done on a grid of about every 4 ft. (both vertically and horizontally) I don't think that any buttressing would be required.

With brick veneer, the air gap is for breathability. Steel containers don't breath at all, which is another reason to put the insulation on the outside; otherwise the cold steel would likely condense moisture on the inside. With earthbags, I don't see the need to leave such an air gap.

Just how you treat the earthbag wall depends on various factors, especially how you design the roof over the building. Probably the best thing to do would be to design the roof with a large eaves, so that the earthbag walls are protected from the rain. If this is done, then the earthbags can be left breathable with an earthen or lime plaster.

I would advise earthbags on the roof only if they are covered by another roof and are there merely for insulation. I would not advise a flat roof and parapets, as this would increase the likelihood of problems and maintenance issues over time. You do need insulation on the roof (even more than the walls). If you really want to proceed with a flattish roof, then perhaps some combination of a moisture barrier (like EPDM) and concrete would do.

Geodesic/Earthbag

Q: I'm really excited about earthbag homes. I'm going to buy a piece of property in Fiji and I think this type of home would be perfect. I noticed in your FAQ section that you thought a hemispherical shape could be utilized "if a rigid framework is provided for it". I was wondering if a metal conduit geodesic frame could be built to handle the loads. By the way I was looking at the straw bale geodesic dome built in Israel.

A: Yes, I think that a metal geodesic framework could be used to support a hemispherical earthbag dome, especially if the size of the metal is adequate. Metal conduit is not particularly strong, so this might not be your best choice...something heavier would probably be better; there are many geodesic kits available. Using earthbags (which can be filled with light-weight insulating materials) is a better idea than using strawbales in a similar situation, because of the potential leaks/rotting issues.

Q: I am wondering about building with rice hulls/earth bags and hybridizing that with geodesic frames to create a reusable 'temporary' structure to side step building codes for off the grid estate building.

A: (Kelly) It seems to me that it is entirely feasible to build a "temporary" structure by erecting a geodesic framework, covering it with lightweight bags full of rice hulls, and then putting a waterproof cover over this. The whole thing could be dismantled and moved somewhere else with a minimum of effort. Whether this would sidestep the building or zoning authorities is a matter of local discretion.

Earthbag/Driftwood

Q: This spring I'm going to build a cabin on a beach on Cypress Island in Puget Sound, (Washington State). I'm trying to use as much local material as possible because it's good practice —and because the only access to the island is a two-hour ride in a very small boat.My plan was to hew planks and beams from the plentiful supply of large, very high quality cedar driftwood on site; my buddy suggested building a sandbag house. I read quite a bit about earthbag construction a few years ago and like the idea so I'm thinking about combining the two.

I'm thinking of making a log-cabin-style structure with runs of sandbags between the logs. The sand bags would eliminate the need to notch the logs and would act as a mortar. Using the bags would also give one the freedom to use oddly shaped logs that one couldn't use in traditional log-cabin construction (I'm thinking of smaller bags to fill in the gaps).

Do you know of anyone that's experimented with this idea or something similar? Also, what can you tell me about building on a beach? Most earthbag structures I've seen are in the desert. I'll be building a ways from the water and using large boulders as-they-stand as a foundation so I'm not worried about erosion, just about moisture and salt-air. What sort of plaster/goo would you recommend for the exterior? I know that papercrete and other commonly used coverings for earthbags won't hold up with constant moisture. —I'll build an overhanging roof of some other material, so I'm not talking about direct rain, just very-high humidity and salt-air.

A: That sounds like a very fun project that you have planned. I can picture it very well from your description, and it sounds quite doable to me. I actually have not heard of anyone doing exactly what you propose. I would think that alternating logs and bags could eliminate the need for barbed wire, since the logs will certainly keep the bags from pulling apart or moving much over time. You might pin the logs to the bags with rebar stakes in critical places, if that seems necessary. It would be nice if the logs would still be visible to some extent, for aesthetic reasons, so that might mean using fairly small bags so the logs are not embedded too far. I would expect that the soil that is on site would suffice to fill the bags. For a plaster, you might consider earth/sand and lime, with a higher percentage of lime on the final coat, as this should hold up pretty well on a protected wall...and it is breathable, which is good in a humid environment.

 


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