Hey Mica, I am also considering the rammed earth tire house with heavy duty truck tires. While some here prefer to use automotive tires, I would like to point out some pros and cons of using heavy duty truck tires.
1. Uniformity. While automotive tires come in sizes ranging from 13in to 16in (and higher,) each of those sizes has sub-sizes in them. If you go to a dump to get tires, there is alot of hunting involved to find all the same size and then strategic placing of tires to keep from having gaps. In your heavy duty truck tires, the majority of your tires are 11R 22.5, Low Pro 22.5, 11R 24.5 and Low Pro 24.5, so there would be alot less hunting involved to find uniform size of tires.
2. Larger size. Since HDT (Heavy Duty Truck) tires are about twice the size of automotive tires, it would take less tires to build the structure. Since the tires are wider, you could run less courses to achieve the same structure height and because the center opening is larger, you have more room to maneuver a backfill tamper which would greatly reduce the amount of physical exertion or if you use a sledge hammer, it gives you more to swing it. Also, the larger size tire gives the wall a much larger footprint on the ground for more stability.
4. Thermal mass. Most people building these homes are doing it for the reasons outlined in the Earthship concept. since a HDT tire is larger, it provides more thermal mass.
5. Upper assembly. Since the center hole is larger, it would be easier to get your rebar through 2 or 3 courses of tires when you are ready to pour your bond beam.
On the downside of using HDT tires....
1. It would take much more earth to fill an HDT tire than an automotive tire.
2. It would use alot more material to pack out the interior walls to make them smooth
3. Where and automotive tire would weigh in at around 300lbs. A HDT tire would probably weight about twice that amount. So while you can make minor adjustments to an automotive tire after packing it in place, this would be much more difficult with an HDT tire.
Now all of these cons add thermal mass to the walls which improves your heating and cooling effects.
Someone had mentioned a heavy duty tire wall would not be as flexible, I don't really see that. It would be just as flexible, have a wider and more stable base, and the casings would be stronger. Of course, all that only matters if you are building your home in an earthquake prone area where a house needs to flex. I have also seen places where some people cut the top sidewall out to make packing easier. If you are thinking about doing this, you need to consider how concerned you are about lateral stress or shifting ground on the home. If you are sure your site is stable, it is probably OK. Again, if you are worried about earthquakes or have other reasons to be concerned with the stability of your site, then you should leave your sidewalls intact. As a personal preference, I would leave the sidewall intact. A few extra hours of labor, sweat, blood and bruising would be worth the mental security over the lifetime of the home.
Now I am a newbie here, and also a newbie to the tire house thing. I stumbled on it about 2 months ago and have been pretty headstrong on it since. I am still in the planning stages of my new home and I am probably suffering from a bit of tunnel vision. So if any of you out there have some insights I need to be aware of, please let me know. Thanks!