Miscellaneous Hybrid Questions and Answers

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

Questions and Answers

Q: I live in the Pacific Northwest where it rains a lot, and I wish to build a green house. What materials could be used in a wet climate? Most of the materials mentioned are for use in drier climates.

A: I used to live in Olympia, so I know about the rain. Virtually all of the materials mentioned do just fine in a wet climate if they are somewhat protected, i.e. with a sufficient roof overhang and foundation. Some of the materials do just fine in a completely exposed environment: these include earthbags covered with either papercrete or stucco, pumicecrete and rockwork, and most of the manufactured systems. For a freestanding solar greenhouse, you want lots of thermal mass on the inside that is well insulated on the outside. So you might consider rocks or adobe on the inside, with pumicecrete or earthbags filled with pumice on the outside. The wall to the south would of course be mostly glazing that can be insulated at night with thermal shades.

Q: I have a foundation 2 x 2 feet, around a 24 x 24 foot pad. I originally wanted to build a cob house, but now, mostly due to time and labor constraints (I have to have it livable by the first of September, I am a single mom, working full time, and I am going to be doing it 80-90% alone), I have decided to do a standard wood frame building (1 and 1/2 stories). Before I made this decision, I had the foundation trench filled in with rock over a drain pipe, and then piped away from the foundation, down the slight hill. The soil is hardpan, I live in Northern California, 3 miles in off the coast. I don't want to waste my $600 rubble trench/french drain, but would, ideally, like to pour a slab over aqua-peck, radiant heat coils. How can I make the MOST use of my rubble trench to do a proper stem wall, WITHOUT having to excavate or trench more?

A: If I were in your situation, I would think about pouring a monolithic, thickened edge slab, with the hydronic system embedded. You could retain the rubble foundation pretty much as is if you make forms around the perimeter of it with rigid blueboard to contain the monolithic slab. Radiant heating systems need to be well insulated from the ground, so if you were able to find some crushed volcanic rock in your area, you could use this to build up the interior portion under the slab so that it will have the appropriate thickness (usually 4-6 inches). If you can't find the volcanic rock, then the area can be built up with compacted soil and more blueboard. That rubble trench with french drain system will keep any water or frost upheaval from being a problem. Good luck with this project. It sounds mighty ambitious for a person in your circumstances!

Q: I am a landscape designer in Austin, Texas. We are involved in a project that includes designing and building a cave at the end of a water slide. It appears that rammed earth or lightweight construction would lend itself well to this application. One of the challenges of this project is that we will have to build a garden on the roof of the cave, and otherwise make it look like a natural part of Central Texas, which includes rocks, boulders and plants. Would rammed earth or lightweight concrete construction be able to support this?

A: I would say that rammed earth (or any earthen structure) would not be a good choice in this circumstance, because of the potential for water weakening the structure, either from the water slide or from watering the plants from above. Lightweight concrete might work, but the design would have to be carefully engineered to accommodate the intended weight. I would actually suggest that the best choice would be a solid masonry structure that incorporates mostly local stones, which can be built into an arched cave-like affair, and would not be in danger of damage from moisture.

Q: I am a grad student in Exhibition Design at Cal State University, Fullerton. In the throes of designing an exhibition space for my final project, I was struck by the possibility of using alternative construction materials for the walls/architectural elements. Google brought me to you. As is always the case in university projects, our budget is minimal. Because the show exhibits contemporary Native American art, I want a more organic or natural feel, not the usual hard-edged masonite construction so typical in the museum world. Some things must be built. Why not explore alternative materials? Long-winded I may be, but I have a feeling you will be able to offer some suggestions, or at least point me in a direction which will yield positive results.

A: One question I would have about your project is, "Does it need to be easily transportable?" If the answer to this is yes, then this would limit the range of materials that you would want to employ. But if the answer is no, then this opens a wide range of possibilities; practically any alternative building method could be used. For instance, a strawbale wall with an earthen plaster would look very organic and natural, and in combination with some natural tree parts or logs could fit your theme quite nicely.

Q: Our plans at this point is to build a hybrid U shaped earthshelter as described in the Mike Oehler's book on PSP using post and beam construction with strawbale on a pumicecrete bond beam.

A: If the strawbale wall is kept from breathing with the polyethylene barrier, it will be susceptible to rotting from accumulated condensation of moisture from within the structure.

Q: I have free access to pumice rock dust, the residue left over from the crushing large pumice into landscaping size rock, (which contains a meager amount of usable pumice for the pumicecrete bond beam). I will have a large amount of this dust left over from sifting out the usable rock. Will this pumice dust make a good backfill material for water drainage around the earthshelter or will it be too small?

A: I built my entire house out of crushed scoria, which is a form of lightweight volcanic rock, placed in earthbags. It makes a great building material because of its insulating quality and the fact that it will not decompose over time. The dust from the crushing process is not as usable because it eliminates all of the air pockets. I would expect that your pumice dust would drain better that the clay soil would, but not as well as ordinary gravel...you might run some tests. Another consideration with this dust is that it might be rather acidic (the scoria dust is) so that care must be taken to eliminate direct contact with with metal, or corrosion can occur.

Q: I am considering building a stick framed (32x36) barn style gambrel roof house, and would like to build on a rammed tire double-U 8ft tall "foundation". It will be below the frost line, buried on 3 sides, glass to the south, maybe topped by a concrete bond beam of some sort. WILL THIS WORK? The house is 21 ft tall to the ridge. I am in western Montana.

A: You can certainly build a rectangular, gambrel-roofed structure on a pounded-tire foundation. I can't quite visualize how you would place such a building on a double-U foundation. I would forget about the earthship U's, and simply make the foundation the shape needed for what you want to build. Just make sure that the foundation goes well above the grade before you start with the stick framing. The bottom plate for the wood frame could be firmly attached to a concrete bond beam on top of the tires, and the concrete should probably be rebarred into the tire wall somehow.

Q: Roofs, a touchy issue for an earthbuilding website. I’m thinking of a roof that looks like a tent from the outside, but in reality is tough and durable and watertight, and can be insulated on the inside against the scorching sun, and UV resistant. So one of my ideas is to make a canvas roof, then stabilize it somehow with with UV resistant fiberglass gel coating outside, and spray-on insulation inside. I have some fiberglass domes, about 3 ft diameter, from an old garden fountain, that have been out in the yard and the sun for 50 years, and show no signs of deterioration. I know about how toxic and yucky fiberglass resins are, but if one could make a roof that lasted 100+ years, there has to be some environmental merit in that, though I’m not trying to convert you, I beg your pardon. But now I’m wondering if ‘flying concrete’ could be used in a similar way. I’m thinking a lightweight, insulated roof is what I want, but I don’t know if the concrete version would be as lightweight as I would like.

A: Southern California generally has a moderate climate, especially if you are anywhere near the coast, so you may not need a whole lot of insulation. One approach to building a free-form, draped kind of structure is to stretch burlap over a frame, and then coat it with successive layers of stucco to stiffen it and make it solid. This can then be insulated with foam. You might need to incorporate some wire mesh in the layers to make it strong enough. This is not a very "natural" approach, but it could create the sort of space you envision.

Q: In my region we have a lot of peat bogs from which we harvest peat moss. I know peat can be mixed with concrete and sand to produce hypertufa. This mix is used to make flower pots, fountains, etc. I wonder if it could also be used as a building material similar to papercrete. Have you heard anything about using peat this way to build homes.... and if so what is the preferred formula and would it resist harsh winters as in my region (New Brunswick, Canada) which get minus 30 Celsius degrees temperatures and lots of snow.

A: I don't have any direct experience with this material, but it sounds like an interesting idea. A quick search at Google brought up several references that might be useful for you: www.taunton.com/finegardening This includes a recipe that uses perlite and fiberglass fibers along with the ingredients that you mention. Another reference shows just the ingredients that you mention. Whether this material would be good for building a home with in your region would partly depend on how good of an insulator it would be against that cold. Certainly the mix that utilized the perlite would be better in this department. Since the hypertufa is intended for long term planter boxes, it probably withstands the riggers of weather pretty well. My suggestion would be to do some experimenting on a very small scale and see what you think. I would like to hear how this works out for you.

Q: Our house was built in the 1940's and has asbestos tile siding. Unfortunately, removing the tiles is expensive and requires a professional asbestos abatement company. The common solution is to side over the old tiles, protecting them from breakdown. If the tiles get broken or weathered, asbestos fibers are released. I am looking for an Earth friendly alternative to boring vinyl siding. I have thought about earth plaster or papercrete plaster but I am concerned about durability and moisture problems. I live in hot-humid Georgia. I don't want mold growing between the plaster and the painted asbestos. Termites are also prevalent in this area. What are your thoughts / suggestions? p.s. I also need to sell this house someday, so that is another consideration to what route I go.

A: I doubt that earthen or papercrete plasters would be a good solution for you in this instance. Perhaps a concrete stucco would provide the sort of extremely durable, water-tight, conventionally resalable covering that you desire.

Q: I have found some interesting homes that incorporate an outer monolithic dome, but build in multiple dwellings within it. I was looking to do something of this sort, but am not sure if sandbags can handle it. Could you get back to me and let me know your thoughts on this?

A: From what I can understand about your idea, the outer monolithic dome would more or less contain smaller units within it. For this to be practical, the outer dome would have to be quite large, likely larger than you could expect earthbags to encompass. It might be that making the larger dome as a conventional Monolithic shell (which can be built to gigantic proportions) and then making the smaller divisions within using earthbags would be practical, but I would have to see  your plans to advise you further.

Q: Have you heard of any home designs using "Concertainer." It is a product used by the military to construct fortification walls quickly and cheaply. It seems like homebuilding might be a good application.

A: This is an interesting idea, but it seems like it might be overkill for residential construction. Something similar and much less expensive can be done using standard earthbags.

Q: I will be ordained a pastor in October. I'll be developing a mission outreaching to migrant workers. In three to four years we hope to start building a community center with a worship space. I'm hoping that it'll be a green building. In particular at this time, I'd like to get some input about building an outdoors amphitheater with recycled tires.

A: I see no reason why an amphitheater could not be built with recycled tires. Just be aware that it is a lot of work to fill those tires with earth and pound them so that the earth is compacted inside. After this you can plaster the tire seats with a stucco of some sort. You might like to get a copy of the "Tire House Book" available from the earthship page for more specific information.

Q: In talking to Colorado Lava I found that scoria can be crushed to various sizes. What size do you recommend for earthbag use and can scoria be substituted for gravel when making an earthbag stemwall for cob construction?

A: I used their 3/4"minus size, but make sure it is as clean as possible of fines, or you pay for lots of useless weight. Yes, scoria of this size works well as a stem wall, and will not wick much water (although the finer stuff will)...the advantage of using it over ordinary gravel is the higher insulation value.

Q: Would that same 3/4 inch size work as fill for a rubble trench foundation?

A: I think you would be much better off with standard gravel, since it has no tendency to wick moisture, is much sturdier and cheaper.

Q: I am building an underground home (from Formworks) two stories and dome shaped with one flat south facing side. This home has steel I-Beams in place and covered with rerod at present awaiting a shotcrete covering. My question is, in place of the shotcrete could I use earthbags and then cover the outside with earth? Would it be strong enough and could you make it water tight?

A: Without knowing quite a bit more about the specifics of your project, it is hard to evaluate. It seems possible that what you propose would work, but I certainly couldn't guarantee it. The strength of reinforced concrete is hard to beat. Covering a steel framework with earthbags would not be as rigidly strong, so that could be an issue. This is a question of engineering that I am not qualified to answer. You can line the earthbags with plastic to waterproof them before backfilling.

Q and A: My understanding has been that thermal mass (K value), greatly outperforms insulation (R value) in terms of keeping a home warm in winter and cool in summer.

Actually they are both important, and must work in conjunction with each other to maintain comfort.

I realize that there's a lot of mass in a scoria or pumice bag wall, just like strawbale.

Neither scoria nor straw bales have significant thermal mass properties.

However, combining insulating material in a massive wall is literally a mixed bag- some insulating value, some thermal mass. Is the mass great enough to basically eliminate heating and cooling costs in a scoria wall constructed home?

A wall with just scoria would not provide enough mass to maintain comfort.

I know that a double wall of adobe blocks with a four inch air gap between walls will keep temperatures above freezing inside a well built structure even when the winters can get down to 40 below zero, all this based on thermal mass performance, which is an entirely different animal than R value /insulative value. My plans had been to build a two rammed earth block walls with an air gap, but now I'm thinking of using earth bags with the dual wall construction. I know- twice the materials and twice the work; the only reason I would have for doing this is to achieve the holy grail of alternative home building: zero heating and zero cooling costs, aside from well placed windows for solar gain in winter. (I don't live where its 40 below, I live at a high elevation in southern Arizona). Perhaps the inner wall made of bags filled with native clay soil, and the outer walls scoria.

I agree with you that this double wall approach could produce superior thermal performance. In fact I designed a house doing exactly what you describe, using inner bags filled with soil and outer bags filled with scoria.

I'm planning on my walls to not be load bearing: I want to try using 55 gallon steel drums welded end-to-end as my roof support and to give extra rigidity to the earth bag walls in the case of seismic movement. Any thoughts?

I think you are better off sticking with solid earthbag walls, with the continuous barbed wire as reinforcement, and this can easily be load-bearing if you want. The barrel idea would lead to discontinuities in tensile strength and also likely problems related to differences in expansion and contraction...especially with steel.

Q: I just acquired an old growth forest property on the side of Mt. Rainier in Washington State. The site is the home of the first two of Craig Chamberlain's prototype "omnisphere" domes, which were assembled there in the late 1980's. These prototypes are constructed from teflon-inter-bolted five-and six-sided spiral fiberglass panels. The design was eventually developed and used for the "dome village" built in the early 90s for the homeless in LA.

My two 20' domes (12' center height) are connected together and built on top of an elevated 50'x32' wooden deck. They are now my permanent residence...but COLD! I want to insulate the domes from the outside (I don't want to change the inside at all, and also don't want to "pierce" the dome structure), perhaps with shotcrete or spray foam, or, better yet, some sort of organic, ecological, artistic, and inexpensive material..rice hull concoction...whatever... preferably a material from the site (but not the ancient and beautiful trees! ;-) or, something recyclable. The location is very rainy and prone to moss, mold, etc. Any advice?

A: Here are a couple of ideas for insulating these domes: The technological fix would be to spray them with a commercial urethane insulation product that would certainly do the job, but not be very ecological. Another approach would be stack earthbags (polypropylene bags) filled with crushed volcanic rock over the structure, and then put a stucco plaster over this to protect the bags and shed the water. This would be very durable and quite insulating, and also utilize a local resource (volcanic stone).  I did something similar to this over a steel quonset building, as can be seen here.

Q and A: My wife & I are soon going to build a 30' x 35' log cabin. We are considering alternative construction for the foundations & basement walls. We plan to use crushed pea stone under the floor & foundation, so drainage & settling should not be a problem. We are comparing,

1. Compressed earth/cement blocks or stabilized earth blocks. (We will use compressed earth blocks for the basement floor)

I would use neither of these for foundations where there is any possibility of contact with moisture over time...even though they are stabilized.

2. Earth - Earth/cement bags

Earthbags filled with crushed volcanic stone or local soil (and insulated on the outside with blueboard) and protected with a moisture barrier on the outside would work.

3. Stone

I feel this is likely your very best option! A double wall is nice for the insulation...or again blueboard can be used on the outside.

4. Combinations of the previous 3. Being in Northern Michigan we need to incorporate a insulation layer which would mean at least a double wall. Perhaps earth blocks or earth bags with stone facing. About 4' would be below grade 4' above grade.

The stone facing could work to protect the bags or the blueboard.

Also should we add buttresses to the walls no matter the construction?

Some degree of buttressing on the inside may be necessary, especially with the earthbags, but also with stone. This can be done with interior partitions to some extent. You might go over your plans with a local builder or engineer.

Q: I would like to build an earth floor and have an idea I am unsure about. I want to lay down a horizontal rows of earthbags, cover them with chicken wire and then papercrete. I will then treat the papercrete with a natural sealant. I want to finish the floor with flagstone, slate tile, ceramic tile or something like that. What do you think? I came up with this myself and am unsure if it will be a viable, durable solution.

A: What you suggest might work, but it all sounds like a lot of unnecessary work. Basically, if you want to have an insulated flagstone or tile floor, it can be done more simply. What I did was first lay down 6 to 8 inches of scoria (crushed volcanic rock) for insulation and tamped it very well, put a sheet of 6 mil poly plastic over this as a radon barrier and to keep the next layer of sand from drifting down into it. The one or two inches of sand is to be able to easily bed the flagstones. Then I filled the voids between the flags with mortar.

If you want to tile it, I would suggest leveling some reinforced concrete over the plastic, and then applying the tiles directly to this. Putting earthbags and/or papercrete under a floor would likely lead to some difficulties that you would rather avoid.

Q: I have been considering the use of urbanite to make an entire basement foundation for a home that will probably be a Timber Frame Strawbale with a footprint of about 30 by 26 feet. The reasons for using Urbanite are many fold yet the structural qualities of it compared to a poured concrete wall are unclear to me. I would be mortaring the urbanite into place yet am unlearn on how I can incorporate rebar into the walls. My stone mason friend says that rebar is very important.

Instead of doing the entire basement from Urbanite I have considered a couple of other options. The first is to do Sauna tubes in all of the corners in the traditional way and then fill in between them with an urbanite wall and then capping the sauna tubes and infilled urbanite wall across with a concrete bond beam.

The second idea is to do Gabions but instead of river rock which is very common here in Missoula Montana I would fill the Gabions with Urbanite and then probably cap that with a concrete bond beam. Basically that would be like a traditional rubble rock foundation that we find here but a bit more modern.

A third idea is to excavate the full basement yet add a perimeter step that is below frost level. Lets say 4.5 feet around the exterior of the excavated hole. On this I could either do the gabions or such and spray the expose earthen part of the step with Gunite or such. As you know according the Earthship building sub soil is usually strong enough to support the load of a rammed earth wall. But I digress. Basically I am looking to make the most environmentally friendly basement foundation possible. I have a good source of urbanite and would like to use it.

A: I applaud your considering the use of urbanite for construction purposes. Several of your ideas seem feasible to me, but your ultimate choice may be influenced by what the building authorities in your area will allow. I would think that any of the plans you outlined would be suitable as a foundation for a straw bale building.

C: (Owen Geiger) Here's a clever building technique in use by a resort in Thailand.  It's an adobe vault covered with a thatched roof. I'm wondering about doing something similar with earthbags/rice hulls to save labor.

Q: I am looking into earthship design with a view to using tyre bales, only one thing worries me about tyre bales, there must be a lot of energy stored in those bales with all the compressed tyres, what if one of the cables holding them together were to snap/erode, wouldn't there be a potential 'explosion' into the living area? Is there a safeguard to this?

A (Leonard Jones): I have been around tire bales a good deal and have engineered several houses and structures from them.  There are a few things you need to know...
1)  After a few months in a compressed bale, the tires tend to take on a "set" and are not very inclined to resume their former shapes.
2)  The tire bales are wired or banded in one direction only.  The bales should be placed in the wall so that the direction of the banding is the same as the long axis of the wall.  Then, should bands or wires break, the adjacent bales will tend to constrain any expansion of the tires.
3)  You should be sure that the tire bales are covered with blown-on plaster or stucco after they are placed - and that the roof is installed as soon as possible.  This will prevent water from getting to the bands or wires and corroding them...

We haven't seen any problems thus far with the phenomenon you describe, and I really don't expect to see any.

Q: We are in the finishing stages of a dome structure that we feel has the potential to be very special. It is partially submerged and incorporates tire construction, papercrete, pumicecrete, and an area that is topped with a satellite dish mounted on a 24 ft virgin log viga. We are having trouble finishing the interfaces between the dome and the window frames, the bottom of the window frames and our papercrete walls, and where the log vigas on the ceiling meet the walls.

A: In looking at your pictures, if it were me, I'd probably fill in that area above the window between the top plate and the ceiling with papercrete, or even fiber-reinforced concrete, and then paint it to match everything else. Under the windows, I kind of like the exposed structure, and would probably leave it as is; another option would be to cut wooden planks to size and box in those spaces to make it look more finished. Where the vigas meet the walls, I would probably fill in the gaps with a mortar mix and paint to match the walls. I like the overall feeling of the space...quite elegant really.

Q: I am interested in building an outdoor patio (with no roof) in SF Bay Area. The patio will be sunken, so I need to ensure proper drainage. For the floor, I was going to go with adobe (sand, clay, water, strawberry bale). Should I put in any other additive? For walls, I was going to go with regular concrete around the perimeter, so even if I mess up the floor, it will not have dramatic consequences. But I'm tempted to explore natural walls. It is possible. Is it strong enough (for built in/attached benches made of the same materials?)

A: I would not recommend the use of adobes as a floor for an outdoor (especially sunken) patio. To last adobes need to be protected from the elements, and they certainly would not be in this situation. A better choice would be more durable bricks, pavers, or flagstone. For walls around this patio I might suggest using earthbags, which can be fashioned into benches and such...or natural stone. The earthbags would need to be plastered with stucco or possibly lime and sand to protect and finish them.

Q: I am building a garage for myself, which is completely poured concrete. I realize, that if it is left as it is, it is going to be very cold and humid inside in winter time. So I decided to put a veneer all over the outside, which would serve the same time as insulation and as a water barrier. My idea is to put a masonry veneer, made out of flat stones glued to the walls with mortar. The thing is that instead of regular cement mortar I want to use clay, putting it 1-2 inches thick between stones and the wall. And the most crazy idea after it all dries I want to heat the joints between stones , using gas torch, in order to harden clay and transform it into ceramic. I live in Russia it is hard to find here stone sealer, so I decided to use sunflower oil, which supposedly penetrates to all the pores of the stones and clay and keeps water out. I am going to brush it all over the masonry. What do you think about all that? Is it going to work?

A: These are interesting ideas that you have, but I think that after all of your work you will be disappointed in the thermal performance of the garage. Adding all of that stone and clay will not appreciably improve the insulation of the space; like the concrete, they are both thermal mass materials that will pass the cold on into the interior. You would be much better off covering the concrete with a truly insulating material, such as strawbales, earthbags filled with crushed light-weight volcanic stone or rice hulls or such. Even commercial insulation board of some sort would be better...

Q: I am a graduate student at Florida State University completing an MFA thesis project on building a semi-permanent to permanent home out of living bamboo with a proposed adobe/cob mixture interior for refugees of natural or man-made disasters. I am currently writing a grant to complete this project in Nepal- where I have an affiliation with an adobe and bamboo research institute. I am writing to gather any information or advice you could give me on the feasibility of my proposed project. I am also highly interested in continuing to create structures with materials that greehomebuilding.com discusses.

A: This certainly sounds like an interesting and a challenging project. I did a little reading about pleaching and found that traditionally it works best with certain varieties of  trees where you can expect that the branches will actually grow together to form a strong latticework. I doubt that bamboo will do this; at least I have never seen it happen. Another problem I would anticipate with trying to do this with bamboo is that most bamboos are vigorous runners, sending up many shoots in all directions to expand their territory, and the occupant of a living bamboo house would need to deal with these intrusions, which have the capability of forcing their way through many barricades. On the positive side, though, living bamboo is much more rot and insect resistant than cut bamboo, so this could be an advantage.

I love bamboo, have it growing in my yard (both the timber variety and a smaller variety), and consider it one of the premier sustainable building materials. But if I were to build a house with it, I would prefer to utilize the cut stalks and allow the plants themselves to grow naturally.

Having said all this, you may find through your experiments that these objections are minor and that you can actually manipulate living bamboo to accomplish your ends.

As for the use of adobe and cob in conjunction with a bamboo framework, this is commonly known as "wattle and daub" and is quite common as a vernacular building method. You should be able to integrate these materials to form a substantial wall, although I could imagine that wind movement of extending parts of the bamboo might present some tendency to crack the earth in places. I would expect that regular maintenance would be required to keep such a structure in good shape.

One last observation is that such a wall system will not really provide much in the way of insulation, so in either a hot or a cold climate, inhabitants would have to deal with the ambient temperature rather quickly migrated inside.

You asked about other building methods that I might recommend. I have a lot of respect for potential of earthbags, for both emergency and permanent structures, and have actually made a site that is just about this: www.earthbagbuilding.com . You might take a look at this and see what you think.

Q: We were wondering if it would be feasible to use Ferrocement with Rammed Earth with the Earthship Designs ( which we love the concept) as we will be on a very tight time frame and will be doing all the work with the just the 2 of us. We would be using the rain catchment, solar/wind, and are thinking of installing a Biogas Unit for the heating and cooking aspect. Would the walls be strong enough with the Ferrocement and Earth ( approx. 2ft thick) to be earthbermed on the 3 sides?

A: It is not clear exactly how you plan to combine the ferrocement and the rammed earth, but I presume the you are thinking of mainly using the rammed earth for the wall and forming the roof with ferrocement. It is not recommended to place rammed earth below grade in general, so to use this in a standard Earthship configuration with bermed walls may not be a very good idea. Usually they use rammed tires for the walls, and these are not adversely affected by possible moisture issues. Also, it is hard to build curved forms for ramming earth, and the standard Earthship has curved walls that are bermed. Another technique for building the walls could be with earthbags, and this option would likely be easier and faster to build than either rammed earth or tires. See www.earthbagbuilding.com for much more information about this technique. Ferrocement roofs are quite feasible and could work well with water catchment designs.

What we were planning was using the ferrocement as forms for the walls and packing them with earth. Then after the bond beam and trusses with 3/4" T&G boards seal and pour 12-16" of Papercrete with a minimum of sand for the roof and then seal with ferrocement also. So the Rammed Earth would be for the thermal mass inside of the ferrocement. As for seal we were thinking on the lines of something like what is used for pick-up beds as its not only waterproof but also handles the dirt and what ever else such as any rocks that may work their way up the walls.

Your idea of ramming earth into ferroconcrete forms sounds good to me. It should be very durable whether bermed or not. As for the papercrete/ferrocement roof, my main concern would be assuring that once the papercrete dries that it remains so. 12-16" of papercrete could take over a month to dry, and this would be without getting rained on. Then you would need to put a moisture barrier over it before applying the ferrocement, or else all the moisture from the cement mix will be absorbed immediately into the papercrete. Papercrete roofs are difficult to achieve successfully, since all too often the best attempts to seal them fail, and then once they get damp, the papercrete can support mold...and if the roof is sealed any moisture that does find its way in there can't evaporate. I don't recommend using papercrete in a roof situation, unless there is a breathable space above it that is protected by a secondary roof.

Q: I am about to embark on a grand experiment on the coast of Maine. I have a few questions specific to this cold, wet climate. Is it possible to have a successful earthbag structure in this climate? I am looking at either a steel frame structure or a reclaimed barn/post and beam structure with earthbag walls and recycled brick vault ceilings between bays. Do you see impending doom?

A: I see no reason why you couldn't be comfortable in an earthbag house on the coast of Maine. Using earthbags as infill in a post and beam structure is entirely feasible, and perhaps more acceptable to your building authorities. Good insulation would be your key to comfort in that climate, so I would advise that both the brick vault and the walls be well insulated. If you can gain access to an insulating fill material for the bags, such as crushed volcanic stone, discarded rice hulls, perlite or vermiculite, then this would provide good insulation, and might even be used over, or under, the brick ceiling somehow (as long as it was protected from moisture).

Another option that you might consider to infill the walls is cordwood, since this may be more easily sourced in your region. The best school for cordwood construction is in New York state, not far from you. See our cordwood page. This has the advantage of producing a good blend of insulation and thermal mass, while creating a finished wall in a one-pass operation. And it is easy for beginners to learn.

Q: I live in Nova Scotia where it can sometimes drop to minus 30 C for weeks at a time. For this reason I realized that a simple cob structure, even with very thick walls would not be warm enough. I therefore decided to do a cob of twelve inches thick wrapped in strawbales. I am going to use a rubble trench and gravel rammed tires for a two foot foundation. Further, I have decided to use earthbags for the interior twelve inches of cob to keep it uniform, for ease and speed of building. The foundation is going to need to be wider than average due to the combination of the earthbags filled with cob, the strawbales and the layers of plaster. This is why I have opted for tires rather than bags for the foundation. I will use two rows of tires (side by side) secured together and then three or four high. Is there any reason that I should not use tires? Also, do you have any comments on wrapping earthbag walls with strawbales?

A: What you have planned will probably work, but there might be better/easier ways to accomplish it. First of all, it is possible to build insulated walls with earthbags if you fill the bags with insulating material, such as crushed volcanic stone (like I did with a house I built in the mountains of Colorado where it also gets very cold), perlite, or even rice hulls. Wrapping standard earthbags filled with adobe-like soil with strawbales should also do the job, but in this case there is no need to bother mixing all that cob with straw...which is a lot of work.

As for a foundation, people have used gravel-filled tires for this, but I am not a big fan of this approach. It takes a lot of filling in spaces around the tires to make a platform, and it is generally unnecessary. Earthbags filled with gravel make perfectly good foundations themselves, and have been used as such for strawbale buildings. If you want a wider foundation you can make two rows of bags connect together with wire. I did this as a foundation for a hybrid quonset/earthbag structure I built once, and it worked fine. With a bag foundation, you get nice straight rows without much fill that fit with the rest of the structure.

Q: I would like to build a home that looks like a timber frame hybrid, but environmentally sound and not near as costly as the typical timber frame homes. My question is, can one be built using the materials you mention on your site (about 2500 sq ft) and still have the strength to support an open great room? Which materials would be best for this type of building? I live in Baton Rouge, Louisiana. What types of materials would be best for building in our climate region (high humidity and heat, hurricanes, ect.)?

A: You can build a simple timber frame to support the roof and walls, using wood that might be available in your region, whether it is milled or left in the round, and then infill the walls with a wide range of materials: strawbales, cordwood, earthbags, adobe, stone, etc. You can combine these various materials in a hybrid house, and it can take many shapes. One advantage of doing this is that it is easier to pass code requirements and also, once the roof is up it will protect the rest of the work.

Practically any of the materials that I mentioned can be employed in that region if the design is right. You generally want to have good roof eaves to keep the rain off the walls, and the walls should be insulated against the heat. Good ventilation is important as well. If I were to build in a hot, humid climate I would consider either building underground, or at least berming much of the home with earth to help keep it cooler. Earthen wall materials and plasters are very beneficial in tempering humidity.

Q: Currently I am part of a group of 6 students tasked with creating a sustainable, eco friendly structure for an orphanage in Haiti. Over the past quarter we have arrived at the conclusion that a earthbag structure with bamboo framing would be the best construction to use allowing for flexibility (in the case of an earthquake or hurricane) while still being sustainable, cheap, and easy to build with readily available materials at the orphanage. We are also trying to fit the building into the context of the area and decided that if possible it would be an inhabitable flat roof. Is there any roof structure that you know of that would allow for this that we can use with earth bag construction?

A: A flat roof that can support habitable space has got to be pretty hefty obviously. Marrying this to an earthbag/bamboo structure would be challenging, but possible. Earthbags can support a tremendous vertical load, and bamboo can be used to provide necessary connections and tensile strength, but neither of these are much good for creating the roof you want.

Unfortunately most roofing systems that can be used for a habitable platform are very heavy, masonry/steel combinations that if they were to fail would crush those below like they did to many during the last earthquake in Haiti. An alternative to this is wooden joist or rafter supported decks with wood sheathing which are then waterproofed with a heavy membrane such as EPDM. These are not locally available, so are not really a sustainable solution. I'm not sure what else to recommend.


Home       Site Map       STORE

For Email contact go to About Us

See this page to read our Privacy Policy

Established in 2001, GreenHomeBuilding.com is primarily a labor of love. Kelly, and the GreenHomeBuilding team of experts, have answered thousands of questions for readers over the years, and we continue to publish up-to-date information about increasingly important sustainable architecture. If you feel moved to assist us in this work, your kind donation would be much appreciated; this can be easily done through our PayPal account:
Custom Search


  [Natural Building Blog]      [Earthbag Building]     [Dream Green Homes]

Disclaimer Of Liability And Warranty
I specifically disclaim any warranty, either expressed or implied, concerning the information on these pages. Neither I nor any of the advisor/consultants associated with this site will have liability for loss, damage, or injury, resulting from the use of any information found on this, or any other page at this site. Kelly Hart, Hartworks LLC.