I have recently become familiar with the use of rice hulls as a material to build with. These unasumming little bits of of debris that are often discarded have found new value as insulation in wood-framed houses and as filler for earthbag projects. They are a durable and renewable material that will not easily burn or decay. They are reported to be about R-3 per inch as insulation, and will not harbor mold or fungus because they don't retain enough moisture to do so. All of this is without any added chemicals...a totally natural product that is often given away. The states where rice mills accumulate hulls include Lousiana, Texas, Arkansa, Missouri, Mississippi, Florida, and California. The hulls only weigh about 9 pounds per cubic foot, so weight is not much of issue in transporting them. They pack into a stable shape when mildly compressed; once they settle into a wall cavity or are packed into an earthbag, they are not shape-shifters.
Don Stephens has been experimenting with rice hulls in bags. He says, "I thought you might find this photo of interest...it's the bag-walled studio I'm mentoring/assisting the owners in building here in Spokane. The bags are just filled with packed, dry rice hulls and they are load-bearing, holding up the insulated bondbeam at the top and the poured-in-ricehull-insulated roof, which will end up planted, over its salvaged-carpet covered Mel-Rol waterproofing. There's been no settlement since construction and it feels SOLID, walking on the roof. The exterior will be stuccoed with slightly-stabilized cob and the interior will be earth plastered. The subfloor is of ricehull-liteclay, for insulation, and will be topped with cob-adobe.... : ) "