Q: Can you use the earthbag technique to build a house of any shape other than domes?

A: Earthbags can be used to build a house of almost any shape, but care must be taken in the engineering design to allow for sufficient reinforcement and buttressing of the walls where needed, such as with buildings that are more rectilinear, with more or less conventional roofs. There are, of course, advantages to domes that are worth considering: they are generally stronger under stresses such as wind or earthquake, they use less material in creating the same amount of living space, and they do not require other tensile materials, such as wood, to enclose a roof area. Even vertical walls if they are curved are inherently stronger, especially with earthbag construction.

Q: I am considering building an earthbag home on remote property near the Snowflake, Arizona area where winds are high and the average temperature is 65F in summer and some snow in winter. Would you recommend a dome structure or a substantial eaved roof for that climate (rains can be hard when they do come)?

A: It depends on what you want to use for an exterior plaster whether a dome or eaved roof structure is better. A dome must have a final plaster that can withstand a lot of weather, so most earthen plasters would not be appropriate; I used papercrete to plaster my earthbag dome home and that worked out pretty well, but this will soon need a harder stucco (or possibly lime) coat to be more permanent.

Q: Can you build double or triple story?

A: I would be cautious in building three stories with earthbags. I know of some two story buildings that seem to be fine, but going much higher than that would require some very careful engineering. Actually, any earthbag house needs to be carefully designed to consider the special requirements of this form of building.

Q: According to the size of the structure, how do you know how much to reduce the size of each row of bags as you proceed up in order to come together at the top to form a dome?

A: Well, there are various shapes that you can attempt to build, and the shape that you want determines how you place the bags. A hemispherical shape is difficult to create because the higher you go up, the more the bags must come in, and it will eventually become unstable, unless there is a framework built up to support it.

Q: In other words, say a structure that measures 20 feet across at the ground level. How do I know how much to decrease each course so that it comes together to close at the top as a dome?

A: The domes that I have made are generally measured with a piece of string or rope, or a rigid piece of pipe. I would first lay out the circular perimeter the way I wanted it, then use the rope or pipe to measure for the placement of the subsequent layers. I basically created an arc, with the fixed length describing it from the perimeter at the base, through the center of the circle to the opposite side of the wall, and rising upward to about the height of one story. At this point I set up a simple tripod of poles to use as a guide for placing the rest of the bags. In other words, the top of the dome is actually a cone, going up at an angle that would allow head space in the loft area, and not come in too abruptly for the bags to need support. I would suggest not coming in any more than a cone that would be described by an equilateral triangle, if that makes sense.

Q: Also, Kelly, in your experience, what would be the biggest diameter you would build without an elaborate support structure?

A: Our bedroom dome is 16 ft. interior diameter and is totally self-supporting. I might try one that is say, 20 ft. It helps having a loft at about the 8 ft. level to tie the structure together at that point and make it more rigid. This also provides more usable space and gives a platform for working at the higher levels.

Q: Has anyone come up with a height /diameter ratio that makes bag building unstable as far as the cone slope is concerned? I plan a circular structure 20 feet diameter (outside measurement) with a 13 feet height to the apex.

A: Not that I know of. Our pantry has a slope of about 45 degrees, which I think would not be stable without the pole framework to help support it. A safer angle would be about 60 degrees, which would make your height about 20 feet. This would be a 1:1 ratio of diameter to height. I would say it partly depends on what shape you want the dome to take. Also, if you want a roomy feeling at floor level, you don't want the walls to come in very sharply.

Q: You built a wooden skeletal tipi type framework above the first floor level of your large central section. Would that be necessary with my 20' diameter X 13' high cone?

A: I had to build this framework because I was working with an ellipse. With your circular project, you might get by without the framework. However, as explained above, your proposed 20X13 project would likely require the framework you describe.

Q: Do you use any kind of bond beam if you are only building walls with the earthbags? How would a roof be attached so that it is not lifted in high winds? (We do get tornados and hurricanes here fairly often)

A: I didn't use any bond beams in my house, but then I built domes. There are several different methods of attaching a standard framed roof to an earthbag wall. This can be accomplished with a reinforced concrete bond beam and tie bolts, or simply using a wooden top plate that is strapped to the earthbags several courses down.

Q: I like the idea of vertical perpendicular interior walls. Actually the floor plan I have in mind is roughly a 48' long by 24' deep, with a largely open interior layout but with two interior walls spaced about 16' apart to break up the space and add a little extra internal thermal mass. I assume these would lend some additional stability to that rear wall if they were tied into the foundation, etc.

A: I'm sure such walls would help with stability. Periodic rebar rods (maybe 3/4") pounded all the way through the bags and into soil and tied to the top plate for your roof, would probably assure that the wall remains intact.

Q: I am wondering if anyone has used the earth bags to build a swimming pool? A friend of ours has a pool built with concrete blocks with a liner covering them. I was thinking that the earthbags would be a great alternative with a much better price. Now their pool is completely in-ground. I would be only able to dig down two feet (really big boulders after that) and then the other two and a half feet would have to be above ground. Do you think this is possible?

A: I didn't build a swimming pool, but I did make a pond by damming a small arroyo with earthbags filled with the local soil and then draping heavy polyethylene over the whole thing. This has lasted some 4 years now. I don't see why this approach wouldn't work for building a pool as well, especially if the pool were circular and several strands of barbed wire were placed between each course of bags.

Q: I know it is possible to build one dome, then add another at a later date. Is this done through vaults and arches?

A: Yes, you have to prepare the place where you might want to join another dome or other structure in advance of actually doing it, i.e. as you are building the first wall. You basically create an arched doorway, and then just fill it back in with more earthbags, so that when you go in later to create the doorway, the opening just needs to be cleared of the infilled bags. Then a small connecting vault or passageway can be constructed.

Q: I'm thinking of using earthbags to make a set of vaults, much like Nader Khalili has done at Cal-Earth. More particularly, I was attracted to the idea of using earthbags for the end walls and load-bearing walls, but instead of using pure earthbag construction to form the roof of the vaults, I'd use curved rebar to form the roof of the vault and overlay that with insulation and a clay-earth mixture. The reason I would like to do it this way instead of constructing the each vault wholly from earthbags has to do with the width of the vaults, which (as I'm planning them) is too wide to permit this (15' x 25' is my working number for each vault).

A: I don't think that even Nader Khalili used earthbags exclusively for his larger vaults. There is just too much danger of collapse. I think he built up walls with earthbags to the spring line, and then did the vaults with stabilized adobe blocks.

Q: How about underground construction? As in a storm or fallout shelter. I am looking for a construction method that can be done individually over time without having to hire any big earth moving equipment or hired help.

A: Earthbags certainly fit this bill, since they can be used below grade and they are easy for one person to handle. You will need to carefully engineer whatever you design so that it will withstand any weight that is placed upon it.

Q: How about waterproofing considerations?

A: Yes, it would have to be waterproofed, and could be done with a few layers of heavy polyethylene plastic.

Q: Has anyone done this already?

A: I buried my earthbag pantry dome, which was covered with plastic and backfilled with maybe 6 inches of soil and gravel.

Q: Have earthbags been used for shoring an underground tunnel or shelter?

A: Earthbag vaults are a bit tricky, but possible if they don't span any more than about 6 feet max.

Q: Or to ask the question another way, if you wanted 2 or 3 feet of earth surrounding you on all sides and overhead, how would you go about building it?

A: I actually would consider burying a prefabricated steel quonset structure, which could be insulated on the outside with bags of crushed volcanic rock, then covered with plastic before backfilled. This sort of thing has been done successfully, as long as the backfilling is done carefully, and evenly from side to side, so that there is not too much stress from any one direction.

Q: I've decided to build with earthbags on our nearly 3 acre lot in Chattanooga, TN. I want to do a serious of domes and kivas. Do you think that I could get away with a 25' kiva that is two story with a bond beam between levels and is bermed into a south facing slope up to ten feet? I know that the round earthbag walls give it better structural integrity, but do you think it is enough to push that much dirt up against it?

A: A circular, vertical-wall earthbag structure of 25' diameter should be very strong indeed; I would say it could easily withstand the pressure of a 10' berm. You would want the bags to be well compacted into place and the use of barbed wire to help maintain integrity...to make it as solid a wall as possible. Also, obviously you would want a moisture barrier between the earthbags and the berm, and possibly some further drainage provided, depending on soil, climate, water table, etc.

Q: I've decided to build a small earth bermed dome (14-16ft diameter) as an experiment prior to starting on our full size home here in Texas. Other than experimentation with the technique itself, the dome will provide shelter while we're working on the other house (we might even decide it's adequate as is and not build any bigger.) I've been looking at the pictures of the interior of your pantry, thinking of using a similar manner of construction. Did you use any form of bond beam or cable to secure the bottom ends of the beams before stacking the bags on the "roof"?

A: No, actually I did not; those beams were just "toenailed" into the bags with some long rebar spikes. For a larger building, or for more weight put on top than I did, a bond beam and/or cable might well be a good idea.

Q: I am wondering if earthbag construction can be an oval instead of a circle. Would this too ambitious for a first-time project? What design or structural challenges would you encounter?

A: The large living room kitchen of the earthbag home that I built was an ellipse, and this turned out to be one of the most difficult challenges of the entire project. Because of the uneven forces inherent in such a shape, I eventually had to create a rigid pole structure inside the dome to force it to stay in the shape I wanted...otherwise it would have been unstable. I generally advise people to stay with circular domes for this reason. However, if I did it, someone else could too...it just requires more careful engineering.

Q: I know that the size of domes are all a matter of personal taste and budget, but I wonder if domes for bedrooms will be sufficient at 11 ft. in diameter. I plotted the sizes of the various domes and they all seemed too small with the admittedly modest diameters. (5 for the pantry, 15 for the living room, 13 for the master bedroom, 11 for the other bedrooms.) Will increasing each of the diameters by half have a severe change on heating and cooling? (I am going to use on-site soil and each room minus the pantry will have lofting to provide some extra storage space.)

A: The bedroom that we happily occupied was 16' diameter, which allowed space for a curved earthbag staircase up to a small loft. A 14' diameter room would allow space for a smaller ladder to access a loft. Anything much smaller than this will not have much loft space. The difference in size should not affect the thermal attributes much. 

Q: My idea: Dig a trench as long as you want and build an earthbag vault.  About 2/3 would be below grade, depending on the water table. Add plastic and backfill on top and then add more plastic and more backfill, plus plants.  What do you think?

A: It turns out that earthbag vaults are not so easy to construct. The entryway to my house in Crestone is a vault, and it was one of the more difficult parts of the plan to accomplish. It only spans about 6 feet, and this is about the most that I would recommend anyone trying. Even Khalili doesn't use earthbags in his vaults...he switches to stabilized adobes. The problem is the same as trying to make very large arched doorways: it is too easy for the bags to deform and you lose the overall shape. Also, vaults put tremendous outward pressure on the walls they sit on, so they have to be quite thick (my entryway had 30" walls) or be buttressed. Of course this wouldn't be a problem in a dug-out pit arrangement like you describe. A carefully designed dome could be completely buried on the other hand. Domes are inherently much stronger in every way.

Q: You have written about the trouble you had with the oval shaped earthbag building due to uneven stresses. I like your Baggins Burrow design and see that this is also an oval shape. Was this the building that you initially had the problems with and was the center support pole the solution?

A: The building that I had trouble with was the home I built in Colorado (pictured here), not the Baggins' Burrow design. At first I tried to build the large elliptical dome without any interior support members, and this is when I ran into trouble. My solution to this was to build a permanent pole frame supporting arrangement to keep the shape rigid. With Baggins' Burrow I have done virtually the same thing, but also added the center support tree, so that there is really no outward thrust on those walls this way.

Q: Also was the double wall a part of the solution?

A: The double walls are mainly to have insulated mass on the inside, but this thick wall should be doubly strong as well.

Q: My husband and I live in Oregon and are building a conventional pole barn with a hefty 8' retaining wall/foundation on one end. We're wondering if an earthbag structure, with reinforcements, is possible, instead of going with a conventional concrete design?

A: It is quite possible that earthbags would work just fine for your retaining wall/foundation, but the design would need to be carefully considered to make sure. 8' is pretty high for a retaining wall, and there can be a great deal of pressure upon this, which is why reinforced concrete is a more sure approach. Two things that can help stabilize retaining walls is to curve them and also to slant them into the hill or berm. Unfortunately neither of these may work for your foundation. If the wall has to be both straight and vertical, then buttressing is an option, but this would take up space within the structure and might be problematic, unless you planned to have stalls or divisions within the barn that could double as buttresses for the earthbag wall.

Q: Pictures of earthbag arches give the impression the bags are nice and uniform from front to back.  But actually they are tapering to create a dome, correct?  If I bevel everything to fit the natural shape of the dome, I should be OK, right?

A: With most of the earthbag arches that I made at my house, I placed the sewn bags the long way over the arch form, so that they were quite a bit thicker than the wall in general. This way the arch was formed vertical and the dome wall traveled along the length of the arch depending on where it needed to go to keep the dome shape flowing. I do remember that on one occasion, with the 6' arch in the bedroom, that I did have to angle the arch bags inward somewhat to allow the dome shape to continue, and this worked out just fine.

Q: I'm still not sure how to increase the corbel size radically at the top of the dome.  As is, we increased the corbel each row, usually 2" and sometimes as much as 3".  It's a little tricky going beyond that, but others have done it so I know it's possible. 

A: You can corbel the bags quite a bit more than 2 or 3 inches, especially when you get that high and the radius is getting small. It is a little surprising, but the tight circles actually don't want to fall in as much as the larger ones.

Q: Another problem is the small circles which require sharp angles.  This causes every bag to be a bit of a struggle working high on a wall in a tight space.

A: I developed a technique of making an angle of the bag fill relative to the bag, so that when the top is folded over the bag actually has an angled top. Then the bags fit together more like a puzzle. With the bag standing upright I would tilt it to one side and shake the contents some to cause it to spill off to one side, then carefully wrap the top bag material down over this new shape to hold it this way until the bag is placed in the circle. You can't really do this with the bottom of the bag, so it is a bit tricky to make it work perfectly, but then the tamping can force a tight fit.

Q: What is the largest dome structure we can build and use just scoria in poly rice bags (as opposed to cob and scoria in poly tubes)? We would like to build it about 18-20 feet in diameter but we're worried about structural integrity. But we will be building a loft, too. Does that add greatly to the structural stability? Then we would have to build it as high as it is in diameter at the base, right? So 18' x 18'?

A: The largest earthbag dome that I know of is one that I build, which is an elliptical one, roughly 20'X30' on the inside. I don't recommend trying ellipses after this experience, since I had to rebuild it once with a rigid pole framework on the inside to help support the shape. With a perfectly circular dome, you should be able to go up to a 20' diameter without too much concern. I built my dome with rice bags filled with the scoria. Yes, a loft within the dome does help support and rigidify the structure considerably. Depending on your design, it will likely be at least as high as it is wide at the base.

Q: This is a sincere request for your input on using earthbag techniques to build an underground shelter.

A: I feel that earthbags are an excellent choice for building shelters that are earth-bermed or even earth-sheltered...but these must be carefully designed and engineered to withstand the incumbent pressures. One major advantage of earthbags is that they are generally not adversely affected by moisture, unlike many other building materials. And, of course, earthbags are a good choice because they are environmentally benign, representing very little embodied energy.

In general I would suggest considering designs that have curved walls, as these tend to be stronger and can withstands the pressures of earth better. As for a roof on an earth-sheltered home or a totally underground structure, this would be a most important element. Domes are a possibility, but burying earthbag domes is largely untested, so there might be some risk here.

Q: I'm an architecture student, and the more I learn about conventional building methods, the less sense they make to me. I'm looking at building my house and I have a question. Can an earthbag dome 25' diameter and 20' high, supported by an internal framework of whole logs every 4' OC, be covered by 2' or more of dirt? What would be the load bearing capacity of such a structure?

A: I wish that I could give  you a definitive answer to your question, but unfortunately there are too many variables to do this. Also, I am not a qualified engineer, so it would not be a good idea for me to offer such critical advice.

If the structure were not to be earth-sheltered, I would think that what you describe would be fine, but with 2 or more feet of earth over it, this is a tremendous amount of weight. Some of the factors that need  to be considered are: exact design of the structure, size and quality of the logs, and how they are attached, weight of the soil to be placed on it, whether the upper part of the dome is reinforced with steel or wire mesh of any sort...

From my experience it is difficult to keep soil up on an earthbag dome because it naturally wants to slide off, so this is another factor.

Q: I'm looking at building a multi-dome home within the next few years. How much weight can a larger( 20-24 foot diameter) support? The reason being I live in the Upper Peninsula of Michigan and we get quite a bit of snow in the winter.

A: You don't say what the dome would be made of. This can make a big difference. Monolithic concrete domes can withstand enormous pressures; geodesics do pretty well, depending on what materials go into their construction; earthbags are perhaps less certain about their strength in this regard. My earthbag/papercrete dome  withstood quite a bit of snow in Colorado, but I built it with a rigid pole framework on the inside.

Q: The trouble I've gotten to is how best to build vaults and domes. I could use falsework to support the vault as it's being built, and then lower the falsework slowly, allowing the vault to shift to carry it's own weight. But that falsework must be pretty damn strong, and therefore not cheap. I don't want to have to add $10,000 for a reusable steel frame, if I don't have to.

A: Earthbag domes are way easier to build than vaults, as they are generally self-supporting while being constructed. I did build an earthbag vaulted entrance to my house in Colorado. This was only about 8 feet wide at the base, tapering up to 6 feet where the vault began, and was two bags wide so that it required no further buttressing. I used a movable wooden form, about four feet long, and released this to go on to the next section. From this experience, I would venture to say that attempting an earthbag vault any wider than this would be very difficult, even as a catenary shape. As far as I know Nader Khalili never built any vaults with earthbags; he switched to adobe blocks or bricks or ferrocement for the vaulted portions of his designs.

Q: The dome may be easier, but as I would be trying to avoid shear stresses to maximize span, the coil of soil has to be shaped uniquely with each lift. Something has to be in place to carry the horizontal loads until the dome is complete, and there almost has to be an 'eye', which would be a rigid frame that can carry all of the compressive loads. All of this becomes very complex. I like the simplicity of a corbeled dome, but it can not be nearly as strong (thus, wide) as a property designed and built catenary (or nearly) version. The math says I can get a 20' radius, 13' high in the center, and still carry the hoop stresses around the perimeter with a 1" steel cable. From your experience, how would it be best to construct a catenary dome?

A: The trick with building a stable earthbag dome is to keep it perfectly symmetrical (circular) and use the two strands of barbed wire between each course. It is the wire that constrains the horizontal forces. The bags of soil can handle all of the vertical compressive loads just fine. The other trick is to not corbel the bags at a rate beyond about a 30 degree angle, making the dome somewhat more conical than hemispherical. This can change for the last few courses at the very top if you want.

C: I think catenary allows a much larger dome. The corbeled dome requires fairly thick walls, and relies on the shear strength transferred by the barbwire. You are missing a great deal of the available strength that is within the bag itself. On paper, a catenary dome 12m radius, 8m high has an maximum internal stress of 336 kPa, (assuming self weight=24 kN/m3, applied distributed vertical load of 6 kN/m2) Using the test results from Colin McDonald at Queens University, one can get 750 kPa from rejected feed bags partially filled with soil. With stronger bags, uniform filling techniques, and the best aspect ratio of each bag, much higher loads are achievable. Thus, the size of the dome can be huge.

The minimum thickness of the wall is estimated by comparing the difference between the catenary and the parabola of that size. The parabola is the right shape when self weight is much less than the vertically applied loads, and the catenary is the right shape when the self weight is much greater than the vertically applied loads. The line of force always acts between these two shapes, regardless of the loads applied. The line of force must always pass within the middle third of the wall. Thus, the difference between these two curves must be less than 1/3 of thickness of the wall. To be safe, we can assume the building is built 'self-loaded only', and the catenary governs, and the line of force acts through the middle of the wall. Only half of the middle third is then available. Thus, the wall should be at least 6x the difference between the two curves, without any further analysis. I get the dome thickness should be at least 8.2% of radius. A more detailed analysis may be able to reduce this substantially, as the applied loads may be significantly less than the self weight.

I was thinking I could use plywood forms during construction. As the height is 4m, I need poles 4m long. When the forms are placed near the bottom of the dome, the poles need to be anchored 2m from the center - use steel rings set at specific radii. Each 4'x8' wide sheet would be anchored against 2 rings, with some overlap in the top corners. 15 sheets would do the first meter of height, all the way around. 12 more would be needed for the next meter, and would sit on the lower tier. A total of 5 tiers would bring it up to less than 5' from the center. One the 2nd tier is complete, the first tier would be removed. It will shift slightly, as the bag's shape change with the change in loading, but I'm pretty sure it won't go far.

A: I hope that you document all of this well when you get around to building this. I would love to feature it at this site and www.earthbagbuilding.com ! I am not trained as an engineer, but what you say sounds reasonable to me.

C: Beware of any unreinforced construction method, especially in earthquake country. You will recall from news stories about earthquakes in many Asian countries that they have high death tolls. This is often because in many impoverished countries metal reinforcement ("re-bar") is omitted, to reduce construction costs. In an earthquake, such buildings just collapse. Sandbag construction and Earthships must be reinforced. This is best accomplished by placing re-bar vertically on two-foot (or narrower) centers through the wall stacks, making sure that the top of each piece of re-bar passes through a wood top sill, or that it is at least firmly wired in place.

A: (Owen Geiger) Vertical rebar through earthbag (sandbag) walls is not necessary, as shown by tests at Cal-Earth and the US Military Academy.  (Please refer to the Earthbag Testing webpage at www.earthbagbuilding.com/testing.htm for more information.)

Earthbag building is exceptionally strong and ideal for survival shelters.  Tests have shown all that is typically needed is two strands of 4-point barbed wire between courses.  Reinforced plaster (plaster with stucco mesh) on both sides and a reinforced concrete bond beam add further strength and is all most people need.  In earthquake regions, Gripple tensioners (a tie-down system) or the equivalent is recommended.

For more information, www.EarthbagBuilding.com has the most complete information on building with earthbags on the Web.  Every major earthbag building system and project, including the EcoBeam method, is profiled.

Also note, earthbag building is much faster and easier than building with tires and rammed earth (‘Earthships').  Not convinced?  Time yourself ramming earth into one tire and compare it to filling and tamping the equivalent length of earthbags.  Multiply this times the number of bags or tires needed in your design.

Q: If one were to use a removable form system, would it work to construct a semispherical dome by tamping each course of bags at the appropriate angle in the way one does when building an arch?

A: This approach might work to form an earthbag hemisphere, but I would never feel totally secure living in it without some sort of rigid interior framework. I did once design and build such a framework for a small earthbag dome that was created with a wooden geodesic framework that was actually quite handsome when finished. I think if you didn't want a framework, then an catenary arch would be inherently stronger and more durable.

Q: What brings me to contact you is curiosity if anybody that you are aware of has constructed, or has considered, a three-story silo-shaped (round) building. Perhaps 25' diameter with poured concrete floors/ceilings at 10' intervals, and a poured concrete rooftop as well.

A: I am not aware of anyone having constructed such an earthbag structure, but it does seem feasible to me. Ordinarily I would caution someone building over two stories with earthbags, but a cylinder-shaped building might be an exception to this, since it is inherently such a stable shape.

Poured concrete floors and ceilings can be very strong when properly reinforced, and these would provide excellent stabilizing diaphragms in your design. With this method, each story would basically be independent from the one under it in terms of calculating wall thickness/height ratios (see below).

I have been pondering and drawing up different wall configurations and am curious as to the effects that changing some variables would make. For example, using oversized bags (24” x 24” etc); double-thickness walls for lower levels;

Thicker walls at the base would lend greater stability. A rule of thumb for earthen walls is that the ratio of thickness/height needs to be at least 1/10; so in your case with a height of 30', the base should be at least 3'.

vertical concrete pillars (or recycled telephone poles) at 10' intervals - especially with straight walls;

As long as these pillars don't interfere with the running bond of the earthbag walls (i.e., either inside or outside the wall), then they could lend additional support. I actually don't think they would be necessary. In a true cylinder shape there would be no straight sections.

including rebar along with the barbed wire to prevent wall distortion;

This could certainly help prevent distortions, but again, with this shape it would probably not be necessary.

installing vertical rebar at 2' intervals on both sides of the sandbag wall and attaching them together to form a cage instead of pounding rebar through the bags themselves (this may also serve as structural reinforcement for stucco).

I have actually considered this idea as a way to provide a rigid guide and form for building domes. I doubt that it would be needed for your cylinder.

Q: I am planning to build an earthbag structure and I was wondering if you could tell me how high is "safe" without narrowing to a dome? Supposing I was to put some other sort of roof on it...

A: I can't give you a definite number for a safe height, because there are too many variables in design that affect this. It depends on the thickness of the wall, the placement of any buttresses or interior walls, whether the walls are curved or not, the way that lofts, second stories and roofs are attached, etc. So you really need to carefully assess all of these things, and you may need the assistance of a knowledgeable engineer. In general, with earthen architecture, you need to maintain ratio of 1:10 in wall thickness to height.

Q: I am going to build a lighthouse cottage on the ocean! The main structure will be round but preferably a little higher than a normal earth bag dome and I am looking at using a different type of roof rather than the dome. I am not really sure... I am also planning to attach a smaller "pod" or two to it. I want to see if you have any recommendations with respect to the best type of roof to use for my design.

A: A circular cylinder of this sort should be quite strong and an excellent shape for using earthbags. This is a fun design. There are many possible roof concepts that would work with this. One would be a dome, which could be either somewhat conical and be made entirely with earthbags, or it could be hemispherical if a rigid framework is provided for it. Another possibility would be a simple shed type roof that truncates the cylinder at an angle. One consideration is whether you want to have a look-out on the roof, in which case the shed roof could be raised enough to provide this. This type of roof would need to be made of other materials than earthbags, obviously.

Q: I'm building my dome shelter by following your instructions in "Building Riceland." Its up to a little over 3 feet in height. I deviated from design by installing another dummy door for later expansion to another dome. Hhow do I interface another dome at the dummy door opening? Pictures at www.autobestbuysweekly.com/Dome

A: As for interfacing the domes later, there are several ways, depending on how you want the space to be arranged. One is with a small vault between the two domes, and another would be to actually overlap the domes slightly, so that the second one rests partially on the first.