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Rice Hulls

by Don Stephens, USA

Featured Components and Materials:

Load-bearing walls - this research structure adopts the basic techniques utilized in earth-bag or "super-adobe"* construction , but with rice-hulls** substituted for the sand or earth typically used to fill the woven polypropylene bags...earth stucco/plaster finish.

Foundation - reinforced rubble and polyprop bags filled with onsite earth.

Floor - adobe over rice-hull/clay base, and one big stone.

Roof - Salvaged steel box-beam, engineered-wood joists, rice-hull insulation, metal top skin.

Natural light - salvaged clear and colored bottles/suntube.

Door, frame, sill, etc. - salvaged.

Ventilation - passive "camel-nose" double tube.

Furnishings - owner-built custom cabinetry.

This project is, so far as we know, a first investigation of the possibilities of rice-hulls as an effective structural/insulating fill material, in the leading-edge alternative/green-building technique of load-bearing bag-wall construction...

The Owner-builders had been attracted to the aesthetic, curvilinear forms and owner/builder-friendly aspects of recent "Oregon Cob" construction for this backyard "sculpture". But while both modern and traditional cob (a hand/foot-formed mix of clay, sand and straw) have proven durability (there are folk-built homes in other parts of the world more than 1,000 years old and several stories tall) and high heat-storing mass, they lack the kind of significant insulation values ideally needed in our climate (much harsher than in Oregon's Willamette Valley or the south of England!)

I've been exploring possible uses for rice-hulls (a generally under-appreciated bi-product of rice milling) for insulation (as they were used in Californinia a hundred years ago) and other construction applications, and recently "imported" a number of tons from the Sacramento Valley. I've also worked with polyprop bags filled with various other materials in previous permitted structural applications. I saw this project as an opportunity to explore these two elements together, creating the curvalinear style the owner desired. (In 12" wide bags they offer an R-value of 36 and are natually fire and mold resistant.)