Earth bags and zoning

I have talked to a few counties so far (in Washington and Nevada in the U.S.) and this is a summary of what I have been told.  Earth bag homes are ok if "properly engineered".  They went on to say that this would probably require some kind of additive to the soil, such as cement or lime, and probably the use of rebar, or some other similar material - maybe to use to "spike" the walls?  This is not a comprehensive survey, to say the least.  What have others found?  I am especially interested in comparing this to what people have found trying to do rammed earth and zoning, earth blocks and zoning, etc.  It seems to me that earth bags are the most friendly, or should I say, the "least hostile" of the alternative building methods.

Slightly related to this - am I hijacking my own thread?? - if scoria is added to earthbags, does it affect the bags strength, either positively or negatively?

A good earth bag home really need the perfect ratio of sand clay and silt to really stick well or 5-7% Portland cement. Natural limestone clay soul seems to work well also. Really at the end if the day if you want it "done right" it's the same mix as eammed earth building. I would say also, I have not visited any of these structures that are comfortable in hard winter or hot summer climates.

Often a lot of energy has to be pumped into the structure or they need to be insulated on the exterior of the thermal mass.

What about an underground house built with earth bags?  Will the soil provide necessary insulation or will something else be necessary?  I would think that the surrounding soil would help provide enough mass to keep the house at a fairly constant temperature.