Geodesic/Earthbag Dugout

C: I was thinking about building a meditation hut using the sandbag method. I'd be interested to know if anybody has tried the following: My idea was to put a small geodesic dome at ground level -maybe 3-4 high and then dig out some of the interior to finally make it 7-8 high in the center. Take the dirt from inside (we have heavy sand here in Bakersfield, CA) and then put those around and on the dome. I imagine, I would have to line the "pit" with concrete blocks reinforced with rebar. I have metal plates that form the centers of the dome sections called "starplates". The reason I wanted to go with sandbags was for silence and also insulation.

R: Well, I think your idea is basically sound...I don't see why it wouldn't work. I helped design a small (14 feet interior diameter) sandbag dome home for a women once, where the top was spherical and used a geodesic framework made of 2X4 lumber connected with metal plates. Bags of crushed volcanic rock were stacked over the framework, and then the whole thing was stuccoed. This worked well. For your project, the whole structure, except for the entrance could be underground. We made our underground pantry by just stacking bags over a conical pole framework, and then covering that with several layers of polyethylene plastic, and backfilling with dirt. If you have available crushed volcanic rock to fill the bags with for the roof section, it would be lighter and much better insulation, but dirt would also work if the geodesic framework is strong enough. As for using cinder blocks and rebar to shore up the underground walls, I would suggest just using the bags again here. That is basically what we did with our pantry, and it has worked marvelously. You could actually start by digging a pit to the level that you want, and somewhat larger than you need. Then stack the bags in a circular pattern and come up either vertically, or leaning in slightly up to the ground level. At this point you can set the geodesic frame on the inside edge of the bags, and continue stacking up and over it. The final thing would be to drape the plastic over the whole structure, all the way to the bottom of the trench, and then toss dirt all over the whole thing. The entrance would need some special consideration, but I'm sure you could figure something out. To keep moisture from coming up through the floor you might put down more plastic there and covering it with carpet or whatever...there are lots of possibilities.

Q: I want to build a 30' geodesic dome made by www.pacificdomes.com, the outside must get an earthbag shell. The inside dome consists of a Fuller construction made of 1'' steel tubes. Does this inside construction withstand the burden of the outside earthbags or what should I do?

A: According to their website, Pacific domes "are engineered with steel frames that withstand heavy snow and hurricane winds". With this in mind, I would say that they could likely withstand the minimal stress of supporting an earthbag shell during the construction process. Once the earthbag shell is completed as a dome, and has been protected with some plaster (hopefully reinforced with stucco netting or such), the whole unit would become more or less monolithic.  I once designed a similar arrangement, using wooden struts for a partial geodesic top to an earthbag dome, and it has worked out quite nicely.

Q: We are researching various methods of building underground housing. I was wondering if one could build a hybrid earthbag/geodesic dome structure. My thoughts were to use the bags to a 9' level, place a geodesic dome on this at the loft level then continue with the bags to the top of the dome. Would a structure as this be strong enough to withstand the pressure of berming with earth?

Also, what about radon in an underground earthbag structure? Are the bags enough of a barrier between the earth and the inside - with of course some type of plaster - to alleviate the need for more than the normal ventilation that one has to put in an underground home?

A: I designed something similar to what you describe for a small earthbag dome, and it worked out well...but it was not earth-sheltered. Geodesics, and domes in general, are very strong structures and can withstand quite a bit of force from above. I would suggest that you use a light-weight insulating material in the bags (such as scoria) if possible, and that you consult an engineer regarding the exact details of the geodesic framework, how it is attached to the bags, and how much soil can be placed over this.

As for the radon issue, you are going to have to cover the bags with a moisture barrier (such as polyethylene sheeting) where ever the structure will be bermed, so this will also serve as a barrier to potential radon. You will want to do the same on the floor area.

Q: I am interested in building a geodesic dome made of bags that are filled with paper-cuts. Do you think this will work and could you give me some additional advise?

A: I am not sure what you mean by paper-cuts, but if they are loose bits of paper, or shredded paper, then they should provide fairly decent insulation, but would not likely be able to bear much weight. This might not be a problem if the bags of paper were used as infill in a geodesic structure that was made with stiff struts of wood or metal. All you would need to do is somehow get the bags to remain stuffed into the triangular spaces until a rigid plaster was placed on both sides...or the bags might be stacked over the geodesic frame, with it supporting the weight of the bags. In either case you will need a completely impervious plaster or membrane on the outside to keep all moisture from entering the walls/roof. Sometimes borax is added to cellulose insulation as a fire retardant, and you might consider this as well.

Earthbag/Stud Wall

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.

.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.

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: 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.

Earthen/Strawbale

Q: My fiance and I just bought land in northern Maine around the 45th parallel. We do not have a lot of money, and are trying to pay as we go. We intend to build a strawbale/cob structure next year but want to build something over the summer to live in for the winter. What is the most feasible, environmentally friendly, resourceful and inexpensive building style/material for this climate? We are considering cob and wondered what the easiest floor to put in a cob hut is?

A: I would suggest that you build your winter quarters with strawbale, which will give you a nice, comfortable place to spend the winter. If you plaster the walls with earthen plaster, and make a rammed earth or adobe floor, then this will also give you some valuable experience for any cobbing you may eventually do.

Q: The only trouble with getting straw bale here is that it has to come by the truckload from Canada. It costs substantially more per bale if you do not buy the whole load but we would not need the whole load for such a small project nor can we afford to buy the whole thing and store the excess. How many bales do you think we would need for a small but livable space? We were thinking cob because we have more of the resources readily available and I am a ceramic artist so have experience building vessels out of clay. How hard would it be to build a small, round, maybe 20 feet diameter cob structure? We are scavengers so will be able to collect windows and other materials salvage. I am just worried most about the floor situation because I am pretty sure we would need to dig below the frost line here, which is about 4 feet down.

A: The main reason that I suggested strawbale over cob for building in Maine is the comfort factor. Strawbales are insulating and cob isn't, so in a cob building, even a small one, you will have to use a lot more energy to keep warm during the winter. The folks who do a lot of cobbing and have written books about it agree that exterior cob shells work best in temperate climates. It is possible to make a double wall of cob, with two separate layers, and stuff the space in between with some insulation, but this is going to be way more work than stacking a few straw bales. Getting below frost level for a foundation can be done with a rubble trench foundation that goes down that deep. Otherwise, it is not generally necessary to recess a floor below frost level, although if you did you would gain the advantage of all that berming for the structure...but unfortunately neither strawbale nor cob are recommended below grade.

Q: I am staying in a hot climate near by the sea and I would like to know if the straw construction can be used in combination with mud blocks? Also, the structure as such, will it withstand the load or can you suggest me some other construction technique that will keep the interior cool. I don't want to dig into the ground as the excavation cost will be too much.

A: The combination of strawbales and adobe can indeed create a very comfortable house in your climate. You will want to use the strawbales for the exterior walls for their insulation value, and the adobe for interior walls as thermal mass. With a good foundation and ample roof overhang, your strawbale walls can be plastered with earthen material as well. Strawbale walls can be either load-bearing or not, depending of the design; I have even seen houses that are both.

Q: Can you suggest to me what shape of building will be good for excluding the sun's radiation? Since I am using straw construction, can it be curved.? Also I want to know if adobe can be used as a vaulted roof in place of a brick roof? Finally, what will be my wall thickness if  I am using straw construction with adobe walls? Will it be economical?

A: You might study some of the material presented at http://greenhomebuilding.com/heatwithsun.htm  that relates to passive solar architecture for your question about this sort of design. In a hot climate, substantial eaves or porches can protect direct solar gain from the windows. Yes, you can construct a curved wall  with strawbales, especially if the curve is fairly gentle, and this can create a strong wall. The wall thickness will be determined by the thickness of the bales themselves, which is usually over 1 foot thick. How economical this will be depends on the cost of these materials in your region. As for the possibility of using adobe bricks for a vaulted roof, this is certainly possible, as has been proven by centuries of Middle Eastern building, but in your circumstance, I would not particularly advise it, for several reasons: 1) Strawbale walls require a substantial eave or roof overhang to adequately protect them from the weather. 2) Adobe will not provide sufficient insulation for the roof area, which is where most of the heat loss or heat gain is experienced in a building. 3) Vaulted adobe roofs are difficult to construct and are vulnerable to water damage, which can cause them to collapse, which can be a safety issue.

Q: I want to know what kind of roofing material to use. Can you suggest to me a material that's cheap in construction and also keeps the interior cool? Also should I go for a flat roof or pitched or vaulted roof?

A: I would suggest that you go for a pitched roof. Often corrugated metal roofing is fairly inexpensive, and you can insulate this with bags of straw, rice hulls, wool, or fiberglass underneath the metal.

Q: I am doing a adobe and strawbale project. Ii was wondering if adobe walls with strawbale insulation on the outside accept glass windows? Also, is it advisable to use glass skylights at the wall and ceiling junctions....will it be structurally safe?

A: Strawbale/adobe walls are a good arrangement, with the straw on the outside for insulation and the adobe on the inside for thermal mass. Glass skylight can be difficult to make water-tight, but it can be done. You may need some design help from someone who lives nearby to suggest the best support for such a skylight.

Q: I want to know if we can use tyres for the foundation if I am going for a strawbale construction? Or can you suggest me some other cheap material that will hold good in a hot climate? And as I stay near the sea, the soil will be saline?

A: Tires have been used as a foundation for strawbale building successfully, and in your situation this might be a good idea.

Q: Will there be any need of providing any air conditioning in the rooms when the walls are made of a layer of adobe and strawbale each, with the strawbales on the outside and plastered?

A: In most climates, and in a well designed house, air conditioning under those circumstances should not be necessary.

Q: Can a house with adobe and strawbale stand on a tyre foundation especially when the front part of the house is elevated? I am sending you a picture of the conceptual sketch of my green house design in which the side and the rear of the house is surrounded by a gutter to take the rain water and empties into the pond in front. The picture has stilts in front. Can I use a tyre foundation and the same in place of the stilts?

A: Both adobe and straw require a solid foundation that completely supports the material, is well above the ground to avoid water, and does not wick moisture into the wall. Tyres can certainly do this, and it appears from the photos that you sent that you have a pretty good idea of how to use them. In a situation where water might collect and you want to avoid moisture rising up through the foundation, you might consider filling the tyres with gravel, so the water can drain right back out, and will not be wicked upward. The idea of the wooden sill plate (especially if it is treated to avoid rot) is often used with strawbale building, but I have usually seen it doubled, so that there are two parallel boards that are the width of the strawbales to sit on....and then space between the two boards can be filled with gravel.

Q: I have to use a sloped roof depending on the wall materials I am using. What kind of roof material would you suggest? The site I have chosen is in India and it's hot and humid there.

A: Often the easiest sort of roof to apply will be corrugated metal, since it is light and durable, and it is easy to extend the roofing to make a substantial eave, which is essential with adobe and straw. It will need to be well insulated from below. Other, more natural materials are also possible, such as thatch, if it is available and if you have the expertise to do it.

Q: The options I had in mind are to use terra cotta tiles or green roofs and the one you had suggested (corrugated sheets). But as you know my design involves adobe and strawbale which is natural. I hesitate a bit to now use modern material for roofing. I feel it would kind of reduce the natural feel of the house. And also since my site is in a hot climatic place I was wondering if I could use earthen pots as thermal insulators in the roofing? If yes how can the be installed?

A: If you have terra cotta tiles available for a reasonable price, by all means use these. All they take is fairly simple framework to support them...but they are heavy so beware. I am not sure what you mean by earthen pots. Good insulation is usually very light-weight material that traps a lot of air, which is why I suggest straw in bags, or something like this. It seems to me that at this point you have a better idea of what is appropriate for your situation than I, since I cannot know with certainty what to do. Maybe you should find some local person who is experienced in this sort of construction to advise you.

Q and A: My question concerns the trade-offs between various natural building methods and how to choose what's best for my particular situation. I'm a 50 year old single woman with some physical disabilities, modest to so-so building skills, and little money -- but a lot of determination! I live in coastal hills of Sonoma County, Northern California, in a forest/grasslands microclimate with 100" of rain from November to May and occasional high winds (e.g., just had a storm with 80 mile winds and 6" rain in one night). Hot and dry summers, with extremely high fire risk. Oh, and just a mile from the San Andreas Fault. I love it here!

I lived for many years in Sonoma county, in Jenner, Occidental, and Forestville, so I know the area pretty well...and it is a beautiful place!

I plan to build a very simple, one-story, 900'-ish home this spring/summer (and need to move into at least a shell by early fall). I plan to do as much labor myself as possible, draft the occasional friends, consult local building experts for advice, hire a helper as needed, and contract the cement work as must. My friend and strawbale advocate Marty Hammer convinced me that load-bearing strawbale is the only way to go. I've been reading new book "Design of Straw Bale Buildings" (Bruce King, et al), and am now full of doubts about MOISTURE -- in particular, my ability to construct something sound enough to hold up to six months of total wetness. The book is full of great details about dealing with serious rain, but I honestly don't have the skill, nor the money to hire the craftsman/woman to painstakingly ensure every connection and frame.

One way to insure a fairly safe building process and ultimately dry walls is to first build a timber frame structure with a good solid roof with substantial eaves or overhangs to protect the walls...then you can infill with the strawbales and do the finish work later without worrying so much about the weather.

I'm also conflicted about plastering -- several coats, inside and out, buckets and buckets, mixing and lugging up ladders, the time involved ... I honestly don't think I'm up to it. If nothing else, it definitely is outside of my time limitations.

You are right that earthen plasters are a lot of work to apply...something that is best done with a crew, whether pros and not.

I've also read "Earthbag Building" (Hunter & Kiffmeyer), and now I've carefully read through Kelly Hart's info here on earthbag building with scoria. Hmmmmm. This may be complete heresy, but here's what I'm thinking: Could I build a post/beam or stick-frame structure as if it were strawbale, but use scoria-filled bags as the in-fill instead?

Yes, you could do this, and the building officials might require it anyway (if you intend to have your house permitted...probably a good idea, given the history that I am familiar with in that region). Earthbags don't require post and beam for support, but they are also not common enough for the building officials to be comfortable with their use either... but as infill, it shouldn't concern them much.

 If moisture gets in, the wall wouldn't rot from inside out. (But would it mold?)

Earthbags filled with scoria will not rot, nor will they likely have problems with mold. I used papercrete as a plaster for my earthbags, and this is where the concern for mold came in.

Could I then use something like fiber-cement panels or planks (Hardie or similar), attached to wood frame, as outside skin? Fire proof (mostly). Do-able for one or two people in short amount of time.

This is possible, but you would need to add a bunch more wood framing to attach this siding to.

Do I want a vapor barrier, or let it alone to breathe?

It is always better to let the wall breath in situations like this.

I plan on plain gable metal roof -- 2' overhangs sufficient? or 4' overhangs on a hip roof (as "Design of Strawbale" suggests as best option for my conditions)?

2' overhangs are usually sufficient, but I suppose that these might be longer for a steeper roof design, like a hip roof might be. The amount of overhang should also be carefully designed to be ideal for any passive solar features you intend.

And here's my final sin: dry wall interior. It can't be that bad, can it? Again, weighing the time involved in beautiful plaster job, vs my need to get it done and move in, this seems most realistic.

You could do a dry wall interior, but again, you would need to add a bunch of interior wood framing to support this, and then go through all of the finish work involved. I don't think you would end up saving any time, and it would cost more to do this. Hanging sheetrock is no fun either. And what you would end up with would not have that natural feeling that I suspect has attracted you to strawbale or earthbags in the first place.

Or cover interior walls/ceiling with reed fencing? Cloth? Or?

This approach might be the fastest of all, and could be done very artistically. It would be easy to experiment with.

BTW, I'm planning on rubble trench foundation (draining to swales) with floating concrete beam.

Sounds like an excellent approach.

And to even up on the green tally sheet, I am now, and will be in future, totally off grid, solar/wind power, gray water system, with lots and lots of recycled items in construction, from wood to sinks.

Good for you!

Q: I am considering a strawbale/cob hybrid house on filled tire foundation in a seismically active zone, and would like to understand better how the walls of such a building could be firmly attached to the foundation, to prevent the entire structure from sliding off during powerful shaking or heaving.

A: I would suggest that you simply embed 1/2 inch steel rebar stakes into the tire foundation and into the ground below at intervals that correspond to the length of the bales, leaving maybe 2 feet exposed above the foundation upon which you can impale the first course of bales or cob. You may need to actually drill through some of the tires to accomplish this. The weight of the building will keep it from lifting off the pins.

Woodframe/Strawbale

Q: We have spent the last year working on our strawbale/conventional hybrid home. Our engineer who has worked with straw before suggested convention framing with OSB on the outside and notching bales with a chainsaw and sliding them up tight against the OSB then finishing the interior of the bale with natural plasters. This is what we have done.

We are about to apply one of our final coats and I have found a problem: we have had a sheetrocking crew mudding our sheetrock (interiors, ceilings etc) and consequently had a huge amount of humidity. We have as possible opened windows but with sub 0 temperatures the last week we can't leave them open long and have the house around 70 deg.

I have noticed that in a number of locations that have not yet received mud on the straw if I push my hand through the intersection of 2 bales I can feel the OSB on the inside and it is frosted with about 1/4 inch of ice is my guess. The straw seems to also be a little wet at that outside edge where it meets the OSB. Am I being over concerned that this is a problem or is it going to be just fine? Please help ASAP as I don't want to move forward until I have some definitive answers.

A: I know of a house that was built several years ago by an experienced carpenter who did something similar to what you describe, using conventional 2X4 framing and T-111 plywood as exterior sheathing, and then insulated the structure with bales laid on end (the studs were spaced to accommodate the bales). Rather than use an earthen plaster on the inside, he wanted sheetrock, so he had to attach nailers to do this. He was concerned about condensation forming on the exterior sheathing also, just as you have discovered, so he opted to place a plastic moisture barrier on the inside before he attached the sheetrock, rendering the house basically unbreathable, but least he felt this would save the bales.

This is a difficult situation, because the conventional wisdom says to keep it all as breathable as possible, but with such a hybrid structure where the exterior is not inherently very breathable, then these sorts of condensation problems can occur and you need to mitigate against this outcome. In your case, where you want the natural plaster inside, placing a moisture barrier there is not so easy, nor am I sure it is the best solution either, since you definitely don't want to trap moisture in the wall. It may be that the best thing in your situation is to go ahead as you plan and pray that it will work out in the end. Normal living in a house produces quite a bit of vapor (from breathing, cooking, bathing, etc.) so there will always be a source of moisture wanting to get through those walls which could condense where it meets the cold outdoor sheathing.

A (Owen Geiger): Well, as you've found out you've broken one of the most important principles of strawbale building -- one of the big things harped on over and over in all the literature -- that moisture must be able to pass through the strawbale walls. There is some leeway in the system if you live in a dry climate, use high quality vents and vent moisture at the source (especially a range hood in the kitchen and bath vents).  A dehumidifier during construction would have been a good investment.  Building during  the summer to speed drying would have been best. I don't know all your climate details, but sorry to say it's likely you are at high risk of moisture damage with few good choices.

Q: Is there anyway I could contact Joe Michalak from Colorado who did the strawbale in-fill. All the information I read says to encapsulate straw with cob so it can breath and resist fire; however Joe used woodchip board exterior and sheetrock interior. I wanted to ask him if these manufactured products can breath also or if he even considered this?

A: Joe used a vapor barrier on the INSIDE to keep condensation from being in a problem in his walls, because they do Not breath.

Q: My wife and I are building an all wood home in Vermont. The walls will be constructed of three sandwiched 1x6 boards running vertically three feet apart. These 'beams' will be exposed on the inside. Outside of them will be 1x8 tongue and groove running horizontally up the wall. There will be rigid foam on the outside of the 1x8 for insulation purposes and then vertical ship lap boards outside this. My interest is closing in the space and creating a flat wall on the inside instead of a series of hollows between the 'beams'. Would this be possible using straw in the hollow and then plastering over the inside wall?

A: I know somebody in Colorado who used strawbales inside a wood-framed and clad building, and it worked out fairly well. He carefully framed the structure so that strawbales fit perfectly between the studs. He also had to put a moisture/vapor barrier on the inside before plastering (he actually used sheetrock), so that condensation would not form within the straw.

Q: This regards straw bale with a wooden frame construction. I know usually you use 2x4 16" o/c for frame construction (platform construction). When using straw bale would you use the same (2x4 16'' o/c)? Or would you spread out the 2x4's wider to accommodate the large bales?

A: Strawbale buildings can be either load bearing (in which case there is no other wood frame component, other than box beams for the doors, windows and the bond beam) or non-load bearing (in which case the most common structure is post and beam with the strawbales as infill.) Another approach involved spacing 2" X material at intervals to accommodate the bales as insulation, but this has some tricky aspects to it that require very careful interior moisture barriers to avoid condensation problems.

Wrapping an Old Trailer

Q: I have been searching the web for any information on Exterior Remodeling an Older Mobile home. We have just been given a 1988 single wide mobile, which we are going to remodel the inside into a recreational room. Its the Exterior siding that I'd like to re-face into something that doesn't look like a trailer. We are thinking about strawbale, but not sure if its ever been done to the exterior of a trailer. Help. Do you have any suggestions. I feel like this is a subject breaking new ground. Since the housing market is off the $$$ charts, why not refurbish old trailers & mobiles and turn them into a useful living space that is befitting to a high-unique living style? Please if you can point me in the right direction I would sure appreciate it.

A: I have been asked this question many times, and the answer is yes, it can be done. It would be a rather major retrofit to achieve, since your trailer would basically need to be surrounded by an entirely new building. This means that an adequate foundation would have to be created, the bale walls (or whatever natural material you chose) would have to be built up in such a way that window and door details would function with the original ones (and detailed to avoid potential moisture problems), and then likely an entire new roof structure placed over the whole building/trailer to assure that the new walls are adequately protected. Given all of this, the trailer should be rather special and worthy of salvage in this way to warrant the work and expense; as you can see, you have nearly created a new natural shell. But I agree with you that salvaging these old trailers is a worthy goal.

C: (Bill Sitkin)I have been accumulating ideas from here and there and want to pass this compilation by you. There are plenty of repo modulars to be had. The perfect one for this project would be one with a high quality interior and a funky exterior.

R: I have put some thought into this proposition, and have had numerous questions from readers of GreenHomeBuilding.com about the idea of retrofitting manufactured housing in various ways. The most common exterior siding used on these things seems to be some sort of painted press-board that holds up fairly well if kept dry most of time. Unfortunately, many of these homes, especially the single-wides, have NO EAVES, and therefore leave the siding completely vulnerable to exteriorization from moisture. I have seen many instances of this problem. Obviously, any retrofitting of these sorts of homes must include a new roof that encompasses the entire unit with ample eaves.

C: (Bill Sitkin)Before setting the home a good sized thermal mass would be installed in the foundation ( at least 6 feet deep).

R: While a concrete foundation obviously provides a great deal of thermal mass, this is nearly useless as far as helping to moderate interior temperatures, since it is isolated from the upper portion of the home. Useful thermal mass must be located within the living portion of the building shell. This is true for basic passive solar designs.

Rather than creating a standard continuous concrete foundation around the manufactured home, I would suggest using insulating earthbags to do the job. They can start at ground level, or perhaps a foot below, if put on sand or on a rubble-trench foundation (depending on soil type). The perimeter stemwall on these things is really not the foundation for the building, since it actually rests on pillar supports located beneath the steel frames on which they are built. Again, this idea pertains more to conventional passive solar designs, than what you describe below.

C: (Bill Sitkin)The home is set and then strawbale walls are added. To protect the bales a second roof is installed with a 2 inch gap between the first roof and the second that extends several feet beyond the bales. The second roof is for a solar hot air system that connects to ducting in the peak that then heats the thermal bank from the bottom up all summer. By the time the bank begins to release heat the colder months have arrived. The key is in creating a control system for the heat source and directing it to the desired areas. A small detail is to use reflectex between roofs.

R: This is an interesting idea, that I am not sure I completely understand, but I believe I get the picture. In this instance you are using the thermal mass of the concrete "foundation" to store heat for release later. This might work in the Crestone area climate, which doesn't really get very hot in the summer. It would likely need an active component of a fan to force the collected hot air down into the area under the floor. I think to be effective, such a system might need considerably more mass than just the concrete...like what the earthships attempt to do with their vast insulated earth berm on the north side, or possibly bins of stones down there. Maybe the actual foundation support for the steel frame could double as thermal mass.

Another considerable challenge with this idea is exactly how to interface the bale wall with the existing door and window openings in such a way that it looks good and is durable over time with all of the potential water issues. The devil is in the details. Probably, the only way to find out if this works, is to try it out on some project.

R: (Owen Geiger) I think Kelly's right.  It's easier (less labor intensive) to add thermal mass inside the dwelling space.  If used as seating, floors, etc. it's very practical. Also, I recommend using trusses to build a new roof on the old structure.  Trusses provide lots of space for insulation. Matts Myhrman's book Build it With Bales briefly mentions wrapping modulars with bales.  I've also been privileged to see his proposal for a Native American community in Arizona.  (The project never took place as far as I'm aware.)  Using his ideas, families would be able to stay on their land and continue living in the modular throughout the renovation process.  The end result is a beautiful, super-insulated southwestern style home that's doubled in size by adding a sun space addition on the south side.

C: (Bill Sitkin) I remember seeing a video that showed a house being retrofitted with strawbales. The windows and doors were relocated into the bales. The depth of the window sills could be varied depending on where they were located. I have to disagree about the thermal mass located inside the building since there is already limited space in a modular. One could pop out the south facing side with a greenhouse that has the mass incorporated into the stem walls and foundation. The cost variable of building rafters would be a negative in my mind. One would still have to bear the cost of a new steel roof whichever way is decided upon. At any rate, I think that retrofitting modulars could be lucrative. I have been looking at the repossessed websites and they are very affordable.

R: (Owen Geiger) Put all doors and windows flush with the outside of the bales to prevent any moisture problems.

R: I actually think that adding a solar greenhouse/heater addition to a modular is about the best of all ideas. I also agree that the larger trusses are unnecessary. There are ways to get mass inside, such as with tile floors, rock-work surrounds for wood stoves, etc., that don't take up that much space. Clearly, money can be made with fixing up those cheap repos in sustainable ways.

Q: I bought a old doublewide mobile home with a foundation and basement. It was the only thing I could afford in the Bar Harbor Maine area when I wanted to move to the coast I love. I saw a lot of potential in the home. I want to reconstruct the roof and bump it up so it has a pitch on it to give me more room. I want to open the front so it has windows and put in double doors and a porch as I have a great view of the bay from my front. I want to do bales of hay around the house and then put on a regular house over that and then redo the interior. I am I being a fool? This will be all that I can afford to live in as the prices of homes here are out of control.

A: What you describe can be done, but there are a number of details that will need to be worked out, especially dealing with an appropriate foundation (as described in another Q and A below) and the need for a roof that substantially covers the new walls, as well as all of the door and window details.

A: (Jeff Ruppert) One of the main pitfalls associated with retrofits is the foundation. If you are in an area with frost heave, you will need to put down support for the bales to frost depth. The other alternative is to sink piers along the wall length and span with a grade beam which incorporates a void form for soil expansion during frost events. If you do not have frost heave issues, it is a fine approach to rehab. The windows work best when on the exterior not only in a retrofit. Good luck!

Q: We had very little money or time to build so we gutted a single wide HUD mobile and are doing low/non-toxic renovations to it. Now we realize that we are going to need a larger place as we will be adopting four foster care children with-in about 6 mos. Do you know of any "green" manufactured/mobile home suppliers or have any ideas on green renovations to an older mobile home?

Tire/Earthbag/Strawbale

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.

Ferrocement/Papercrete/Tile

Q: My husband & I are looking into building a ferrocement dome (modular units). What do you feel is the feasibility of sandwiching a layer of papercrete blocks between 2 layers of ferrocement? Since we are potters, ultimately ceramic tile and grout will be used for the finish. The wall would probably end up over 12' thick. I am aware that papercrete wicks moisture. Will this effect the ferrocement? I envision the dry papercrete wicking moisture too quickly from the outer layer of cement as the cement is applied. Then again. if the papercrete is moist as the last layer of cement is applied, will the papercrete ever have a chance to dry out being stuck between two layers of ferrocement?

A: It is an interesting concept that you propose. There would certainly be advantages to the arrangement, if it could technically be accomplished. With the ferrocement on the inside you should get plenty of thermal mass, and the papercrete would provide the insulation. The trick would be to get the papercrete to dry out after you poured the final coat of cement, and this might be quite difficult; some formulas of ferrocement are virtually water proof. My suggestion might be to forgo that final coating of ferrocement, and allow the papercrete to be the outer layer. This papercrete could be done in a couple of pours, so that the first one is highly insulating, with mostly paper and little mineral material. The next pour could be more much more sand with the paper and cement, to give a more durable, fireproof layer. This is basically what I did with my house, and it has worked out well. If the initial ferrocement shell is mixed to be waterproof, then you could simply allow the papercrete layer to breath and evaporate moisture as needed. Sealing it to moisture would be another option, but any water that does manage to get through might be trapped there for some time. This might take some experimenting, perhaps trying it unsealed at first, and the sealing it later if this seems necessary.

Strawbale/Stone

Q: My question is whether or not strawbale would make an economical and practical inner wall (and insulation) with load bearing stone walls (either traditional or slipform)as outer walls...would the inherent condensation from the stone walls endanger the strawbales? Would a 1/2 inch space mitigate this danger, and have you ever seen this method used?

A: No, I haven't heard of this particular approach to building a wall. Your concern about condensation forming between the materials could be justified, since the cold rocks would tend to make this happen. An interior vapor barrier may be necessary. Trying to leave a small space between the rocks and straw might be difficult to achieve, given the unevenness of the materials. I always advocate putting the insulation material (straw) on the outside of the building envelope, with the thermal mass (rock) on the inside. If the straw had a somewhat breathable plaster on the outside, I don't think that condensation would be a problem with this arrangement, because the rocks would not get cold enough.

Q: Can anyone tell me if it is possible to build a strawbale home and slipform the front w/stone? I have searched through many book options, but I would really like to marry the two concepts I love, stone and strawbale, and would love to utilize as much of natural resources as possible. Would the stone be an option instead of stucco?

A: My recommendation would be to reverse the order and put the stone on the inside so that it will act as thermal mass in the house, with the strawbale insulating it. In this way you would also eliminate the potential problem of condensation affecting the straw. Put a breathable plaster on the straw and you will have an extremely efficient house that will last a very long time. In this way, I don't think that you need any gap between the stone and the straw.

A: (Owen Geiger) Stone/straw combo is not common and seldom discussed, so there's little if any body of knowledge to draw from.  My guess is it's similar to wood siding. I think a small 1/2" gap between the stone and bales would allow moisture to escape/drain. One obvious drawback to this idea is it creates excessively massive walls.

Q: I am interested in building a stone house. I have questions about what the cost will be. We have the cement mixer, and land- but probably not enough stone. I would like the house to have a full basement- out of cement possibly but was hoping something natural like strawbale might work. I was thinking that I could set the ground level outside the perimeter of the basement level to avoid the added stress of the structure. However, we will only be able to hire out for less than 1/2 the work. I wanted to basically do a 2 story house w/ basement with at least 3 bathrooms.

A: While it is true that stonework can be inexpensive, it is also very time-consuming. This fact, coupled with the fact that the stonework is really only a fraction of all the work and material that goes into to making a house, the cost of making such a home will not likely be much lower than a conventional home, if that. Certainly doing much of the work yourself can reduce the cost, perhaps in your case by as much as 1/4...

Strawbales are not suitable for any basement construction; they are too vulnerable to eventual rot. But they are great for a well-insulated shell of an above-ground home. My suggestion would be to design your home with concrete or stonework for the basement, and do the first floor with strawbale. Some interior stonework on the first floor will provide needed thermal mass to keep the home comfortable.

That makes sense for the basement. Also for the first and second floor- straw bale for an interior as an insulator will work? Keep everything warm... Is 3500 sq feet  feasible - structure wise? I would like it to be 2 story. My concern from what I've read so far is that the further up you go the structure becomes a problem. Will straw bale on both levels be a strong enough support? Also, is there a way to "fire/ moisture" proof the straw bale interior?

I was picturing just the basement with one story above that when I suggested the strawbale upper portion. Strawbale building rarely goes above one story. My idea was that the basement would provide the foundation for the upper story. The strawbale would ideally be exterior, since this is where you need the insulation. Stonework would be on the inside. But if you want a basement plus two stories, then the first story should probably also be stone, although any exposed stone building needs some form of insulation to make it comfortable. This can be accomplished with an interior core of insulation sandwiched between two layers of stone...a very time-consuming and likely expensive project, especially for a house as large as you want. Anyway you look at it, you would be embarking on a MAJOR project. Strawbales are surprisingly fireproof, because of lack of oxygen in the bales, but then they can be made even more fireproof by plastering them with an earthen plaster.

Tire/Papercrete

Q: I have been thinking about all of the different types of alternative building materials. Two of the materials that I am interested in are tires and papercrete. My first question is, is it possible to combine these two materials? By this I mean, can I build a structure with tires and fill them with papercrete? My thought is that I want to produce a structure that uses inexpensive materials and that I can build myself. I also want a solid structure that would provide a good insulation from the outside environment. Can you give me your thoughts on my idea? Is it feasible? What would be the downside of this method?

A: I wouldn't recommend filling tires with papercrete for several reasons:
1) It would take forever to cure, since it couldn't dry out very well in the tire.
2) For the same reason, it could become moist and harbor mold over time.
3) Papercrete does compact with enough weight on it, so this might be an issue.
4) Earth is much cheaper and easier to come by for filling the tires.

On the other hand, I would think that papercrete might work quite well as a plaster to cover the outside of a tire wall.

Q: We are hoping to build an above ground hot-tub using tyres as the walls. I am concerned that if I fill them with earth the thermal mass will soak up all the heat from the water and I am struggling to think of a suitable material which will provide both the mechanical strength and thermal insulation required (both below the tub and in the walls) (I've not found a supplier of pumice in the UK). Do you have any suggestions or know of anybody who has undertaken a similar project that I may contact? Would papercrete be suitable and if so what slab thickness would you suggest?

A: You are right about the mass in the tires filled with soil soaking up all the heat from the tub, unless there is some form of insulation between them. Papercrete does indeed act as good insulation, but only if it is kept absolutely dry, which may be a challenge in such a situation. In fact if the papercrete stayed wet and warm long enough, it could support mold, which definitely not be good. I am planning to build a hot tub using a plastic stock watering tank to hold the water, then placing some insulation (possibly pumice, fiberglass, or styrofoam), and then doing mortared rock work around it. Making such a tank with completely natural materials is a challenge.

Strawbale/Earthbag/Cordwood

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.

Tire/Concrete Block

Q and A: I am living in Baja California by the Sea of Cortez. Most of my indoor living is in two concrete block rooms which are what was here when I moved in. The immediate problem is the west wall which becomes as hot as an oven even this early in the summer. I have been thinking of adding a second wall of tires (Mike Reynolds style) outside the concrete block, followed by stucco. Do you think this would work well or do you have any other ideas?

This would definitely help, mostly because of the thickness of it. Tire walls provide mostly thermal mass and not much insulation, but the thicker the wall, the more stable the temperature will be. If you do this, you might stack the tires a bit away from the block wall to provide an air gap that will serve as an insulated barrier in transferring the heat.

Besides insulation, the humidity gets almost unbearable; should I use a plastic barrier between the tires and the concrete block?

I am more of a fan of maintaining breathability in wall systems, as I believe it is healthier for both wall and inhabitants. The humidity is in the air, and is therefore going to find its way inside anyway. A plastic barrier will just trap the moisture that gets into the wall. You might investigate forms of dehumidifiers to deal with this.

Besides heat and humidity we have some really nasty bugs here so I have to do what I can not to provide homes for them. A good solid stucco should stop the bugs from entering the wall. Any quick ideas or recommendations of reading/videos would be appreciated. I have a fairly extensive library about alternative building but, as often happens, I am left wondering about specific questions for my particular situation.

A much simpler solution that you might want to try as a first step is a paint-on insulation. I have recently found out about this, and in fact have a link to a company that makes it: the Insuladd product.

Q: I current live in a small ranch style home built in the 50's. It is a true brick house, which means it radiates cold in the winter right through the walls. Is it possible to clad the outside with the tire wall technique?? I do realize this would require a redo of the roof system to accomplish this.. Has anyone else done a conversion like this??

A: What you really need to make this house comfortable is to wrap the bricks with something that will insulate them from the extremes of temperature, both cold and hot. While a tire wall would help, this would not be the best solution; a more insulating material, such as strawbales, earthbags filled with scoria or rice hulls, or even commercial rigid insulation would do much better. All of these solutions do require a subsequent plaster on the outside to protect them, as well as a likely roof extension and a proper foundation...so this is not a simple job. Many people have done this.

Stone/Adobe

Q: I need to find an insulating material for my stone wall basement. I don't want to cover the stone with dry wall. I would consider adobe or some other natural material that might provide some warmth.

A: Adobe would not make a good insulating material, so unless you left an air space of several inches between it and the rock wall, it would not do very much good. Of course doing this would diminish the interior size of the room noticeably. Most any insulating material, natural or otherwise, would need to be covered with something else to make it look good. One approach would be to put a relatively thin layer of insulation (such as blueboard) over the stones, attaching it as firmly as possible, and then put wire mesh over this and plaster the wall with an earthen plaster. This would give you the adobe look and feel without taking up as much space. The best approach would be to dig around the basement and insulate the wall from the outside with blueboard or something similar, although this may not be feasible. This way the interior natural stonework would remain the same, you would not lose any space, and the thermal mass of the stone would work to your advantage on the inside, being insulated from the ground.

Wood/Straw/Papercrete

Q: I want to build a permanent tipi using tamerack poles. Could I cover the poles inside & out with chicken wire, sandwiching flakes of straw in between, & plaster the whole thing with papercrete?

A: This seems like an interesting idea that might well work, especially if you live in a relatively arid region. The main concern would be moisture possibly wicking through to the inside. I know of straw bales being successfully plastered with papercrete, so this should work. I would suggest that you make sure that the straw is thoroughly stuffed between the wire and poles, so that at no place is the papercrete solid from inside to out. If you try this and moisture does seem to be wicking through, you could try to seal the exterior papercrete with something, but this is not always easy to do. This would be an experiment... but one worth trying. Let me know how it works out.

Strawbale/Steel

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...a