Hybrid Questions and Answers Involving Tile

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



Concrete Block/Tires


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Q: In the future I hope to build an "Eco-dwelling" somewhere in New Mexico. I have an idea about doing the walls with rammed-earth tires for about 2/3 the height of the wall and then doing the upper 1/3 of wall with minimal wood framing and straw bales. I also hope to have an earth-berm roughly to the height that the bale wall starts at. So my question is, do you see any major ( or minor) flaws in this design?

A: I see no problems with what you have in mind. People have used packed tires for the foundation of strawbale walls with success before...just make sure that the earth-berming is kept well below where the bales begin.


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.

Concrete Block/Tires

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.

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.


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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.