Hybrid Questions and Answers Involving Steel

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

Earthbag/Papercrete/Steel Quonset Vault

Earthbag/Steel Container


Stone and Steel

Cordwood/Steel Container


Earthbag/Papercrete/Steel Quonset Vault

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: What are your thoughts on climatic considerations for building the carriage house in Memphis, TN? It gets very hot and humid in the summers and can get down to the single digits on occasion in the winter, with occasional but usually light snow. I'm worried about moisture problems with the dome structure and condensation from the humidity in the summer. What area is the carriage house you built in and how is it holding up?

A: The original Carriage House was built in the mountains of Colorado, at over 8,000 ft elevation, where it gets very cold in the winter and mildly warm in the summer. The climate is rather arid, with only about 12 inches of precipitation a year. The bags of scoria and papercrete covering provided quite good insulation in this climate, and there were never any condensation issues. We have since sold that property and the new owners have placed a secondary stucco covering over the old papercrete, which provides a more durable exterior surface. Papercrete generally doesn't do well in very humid climates because it can support mold if it stays damp too long. I would think that a stucco finish might be preferable for you.

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.

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.

Q: Our quonset is insulated on the interior with what appears to be R13 fiberglass batt insulation. There is also a vapor barrier on the inside but we have concerns with the quality of the insulation and vapor barrier installation. We are unable to access all of it because the interior is already finished and we would like to avoid having to demolish and rebuild the existing interior. There appears to be no ventilation for the cold side of the insulation (the space between the metal roof and insulation). There is no insulation currently on the exterior (the metal of the quonset exterior is painted and directly exposed to the elements (but does not have any leaking issues during hard rains). We have only noticed the condensation when it freezes at night and the sun comes out early in the morning and heats the roof quickly. What can we do?

A: I'm not surprised that you are having problems with this. R13 fiberglass batts don't provide sufficient insulation in that climate in the best of worlds. It is nearly impossible to keep moist interior air from infiltrating through to the cold metal, and thus the condensation. Foam insulation sprayed on the inside is the typical way the manufacturers of metal building recommend insulating them. But I don't blame you for not wanting to tear out what is there and start over again. If it were me, I would leave the interior well enough alone and concentrate on insulating it better on the outside, either with bags of scoria and stucco over this like I did, or have some commercial spray foam put on the outside, protected by durable paint or stucco. This is basically what the Monolithic dome people do with their ferrocement domes, so it can work.

Q: Could a Quonset hut support the weight of two 12” layers of corbelled scoria bags on the exterior? Or laid radially? If not, what would be an inexpensive yet effective means of reinforcing the metal in order to do this? And do you see any problems with this idea?

A: I did something very similar to what you describe when I built my Carriage House, which you can see at http://dreamgreenhomes.com/plans/carriagehouse.htm  This concept worked out quite well and insulated the structure to be comfortable in a very cold climate. You can see from the diagrams that I raised the entire Quonset structure up on an earthbag stem wall. I also did provide substantial bracing at the point where the walls start to curve inward.

Q: I’d love to leave the exterior of the Quonset hut exposed in order to catch rainwater (I live in southern Arizona) and just do the end cap walls in scoria bag. In that case, is there anything I could do to keep it cool in the summers, other than interior insulation? I don’t see why it couldn’t be partially buried (using the P model which has vertical walls before doming over the top), and I could orient it to be south facing, but I wonder if that would all be enough to keep the home cool enough to forego AC. I guess I’m just trying to figure if a Quonset hut home makes sense in the low desert using only passive solar design for cooling.

A: I'm sure that you could partially bury a Quonset to gain thermal advantage. If the metal roof were exposed it would still require some form of insulation to be comfortable. I suppose that it might be possible to fill the voids formed by the corrugations of the roof with some lightweight insulating material. The easiest approach would be spray-on foam, and there are some ecological choices for this, such as soy-based foam. You could get quite a bit of solar gain from the end wall if it were mostly glass.

Q: Is the Quonset shell used in the design a 16 X 13 S type or 16 X 11? To meet the local code requirements I would need to either stretch this design out to 50 feet long, which is fine, but I was wondering if there would be any problem adapting this design with a wider quonset perhaps a 30 x 16 model? If scoria is hard to source at the build site, can you recommend some alternate gravel type that could substitute? for example I don't see many bulk sellers of scoria but lots for "Red lava aggregate"?

A: The Carriage House that I built was based on a 16' X 34'quonset that only had about 4 feet of vertical sidewall before it curved inward; many S models have much higher sidewalls. If you started with a higher S model you might be able to dispense with the earthbag stem wall. You might be able to adapt the design to a wider model, but I would not go more than about 20' wide, as that is about as long as you would be able to find for the joists. "Red lava aggregate" is probably either the same or very similar to scoria.

Earthbag/Steel Container

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.



Q: Hello, what a great site... I am currently working with an architect and have just gotten out of Peace Corps. I want to start building a house in Austin Texas and am wondering if building it with steel construction and straw bale is a good way... I haven't really seen or heard of this yet and am wondering what you thought about it. This will be my first house to build and am going to become a general contractor and an architect in the future.

A: I would encourage you to try this out, since most strawbale homes still use a lot of lumber (only about 20% less than the typical wood-framed house) and using steel for framing could save some trees. The trick to successfully combining these materials would be in making sure that such details as eliminating any thermal bridges of steel from the inside to the outside, or any possibility of condensation forming on the steel that could accumulate in the straw. Another possible problem could be differences of expansion and contraction where plasters might crack. Placing all of the steel toward the interior of the building might solve some of these concerns.

Q: I would like an opinion/thoughts on using strawbales as an insulation product for a standard Sheet Metal Covered Pole Building. After "stacking and packing" the straw, build perlin structure on the inside that could be covered with sheet metal/Sheet Rock, depending the application. I am sure there are "goods and bads" to doing this.

A: When you make a hybrid building combining straw with non-permeable materials like steel you risk lots of problems related to moisture through condensation or lack of breathability...and this depends to some extent on your climate. With straw it is better to keep the wall system breathable.

That makes complete sense. I was worried that all the air leaks of a metal structure would loose R Value. You bring another very good point that since the metal would provide rapid changes in temperature due to the weather, the metal would sweat, generating moisture, possibly mold, and other issues.

Q: I have this old metal warehouse, 24x30, that I want to use a bale wall inside, with earthen stucco. I am worried about bugs and critters getting in from the outside.

A: A steel building is generally impervious to critters, so as long as all of the joints are tight I don't think you need to worry. A greater concern might be condensation forming between the bales and the steel if you live in a cold climate. Ordinarily you want bale walls to remain breathable to avoid this problem. You might possibly place a vapor barrier between the stucco and the bales, but this can be tricky to fully accomplish.

Q: I’m interested in the idea of combining steel containers with straw bale insulation, mostly because steel containers as structural components seem to be less expensive and less complicated to implement than timber framing—but has anyone done this successfully and had it for enough years to  show that the moisture issue can be overcome?  And if so, how?  I live in the BC Interior where it is moderately cold and wet a good portion of the year.  I have also, btw, lived in a steel container surrounded by unadobed bales but it was in the Mojave desert and I tore the whole thing apart after a year, so permanence wasn’t an issue; in fact the impermanence was desired.

A: (Kelly) As I'm sure you know, strawbales should ideally be able to breathe from both sides. If they are up against a steel container this would be compromised, so that they could only breathe on the outside really. The only way that I could see this working in your climate would be to clad the bales with a "rainscreen" between the siding and the bales which allows air to circular between them. Also, some sort of roof that positively sheds all water well away from the structure would be necessary. I have never heard of anybody doing this, but it might have been done.

Stone and Steel

Q: We are planning to rock our metal (26 gauge) house with limestone. Do we need to put up any type of moisture barrier between the metal and mortar to prevent the metal from rusting over time. Will the mortar effect the metal in anyway?

A: I hope you will have some insulation in there somewhere, or this will not be very comfortable. I would suggest that you put a moisture barrier between the metal and the stone, just as a precaution. This will eliminate any corrosion of the metal that might occur from the alkalinity of the mortar and limestone. Also, it will keep any moisture from condensation against the metal from tending to corrode it. The stonework will breath some, so any moisture that does form there will have a chance to dissipate.

Cordwood/Steel Container

Q: I live in Eastern Tennessee. I have purchased several 40' steel shipping containers with the intent of converting them to a house. I am wondering about building cordwood walls around this strong exterior structure to provide thermal mass, insulation and improved aesthetics. My thought is to build a concrete block footer to get the logs away from the soil. The container would be on piers, providing an open crawl space underneath. Is there a method you could recommend to anchor the logs to the steel skin and frame that would not require a timber frame?

A: I think that what you propose is entirely feasible and practical. Such an external cordwood shell would definitely help insulate the metal container in very aesthetic manner. It would add some thermal mass, but not a whole lot. The cordwood walls would really just need to be self-supporting, since they are not necessarily part of the structural integrity of the building. It would not require much of an attachment to the container, only enough to connect the two together, and this could be accomplished with periodic metal bars (angle iron, etc.) that was welded perpendicular to the container wall and imbedded within the cordwood. You can actually stack cordwood at the corners in such a way that they interlace directions and are self-supporting. Whatever roof structure you devise would obviously need to extend over the cordwood walls.


Q: I have a 100 foot by 30 foot by 14 foot high steel building. I am interested in making it a "green" building. Can you offer suggestions, references,etc.

A: What you might do to retrofit this building would depend mainly on how you want to use it. As a warehouse it may not need anything done. As a shop, it may just need some form of insulation to make it comfortable. As a residence, it could become the basis for a complete redesign that would employ many principles of sustainable architecture, such as passive solar design.

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'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 have a metal building that I want to insulate. Can I use a straw clay insulation on the inside right up against the metal?

A: The problem that I can foresee with this is that if the metal gets cold (which it will if it is exposed to the outside air) then moisture will likely condense on the inside between the straw and the metal. This moisture then might tend to rot the straw over time. This might be avoided either by also insulating the outside of the building so the metal stays warmer, or somehow placing a continuous moisture barrier over the straw on the inside so that the inside air can't reach the metal...but this is hard to reliably achieve, and it might aggravate the problem of moisture and straw since then the interior wall is completely unbreathable.

Q: I have the opportunity to move into a metal shop.  Well, to use a part of it as a home, anyway.   Am wondering what natural  building methods I might use.  It has no insulation.  Had thought of cob, wattle with clay, or clay slip.  But would the metal on the outside keep it from "breathing" ? This would be done in Northwest Louisiana.  Too much humidity for straw bale building.   At 72 do not want to try earthbags.  And I guess it might be the same as with the others....metal keep it from breathing ?

A: Yes, metal buildings will inhibit a wall's breathability. What you need is insulation, probably on the inside, that will be protected by the metal. This could be in the form of bags of perlite, scoria, or rice hulls.  Other options might include soy-based foam insulation or other commercial products. Then adding some interior thermal mass, such as earthen plaster, lime, bricks, etc. will help with keeping the interior environment stable.

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