Yesterday’s blog post on Production Earthbag Building using Rice Hulls introduced one method for building walls with rice hulls. As you can see from the drawing above, the construction process is very straightforward. This method uses a standard post and beam frame with posts set in concrete footers and beams attached to the posts with post caps. The post and beam frame is carefully laid out, plumbed, leveled and squared to achieve good results. The roof is built after the concrete footers have set up. While you’re waiting for the concrete to dry, you can fill the gravel bags or tubes that help protect the rice hulls from moisture damage. Use double bags or tubes for added strength. You can fill the tubes with scoria or pumice in cold climates to create an insulated foundation.
With the roof and gravel bag foundation complete, now you’re ready to fill the rice hull tubes that wrap around the post and beam frame. Tie each tube to each post with baling twine. Fasten tubes out of sight on the backside of the posts to maintain the beauty of the wood frame. 6-penny common nails would work well for this purpose. Drape pre-cut lengths of baling twine every 2 feet or so for later attachment of plaster mesh. You can also use baling twine to tie the tubes together for added rigidity if necessary. Work carefully to keep everything in alignment so there are no bulges in the wall. If you do get some bulges, they can be dealt with by tying opposing dowels, bamboo or saplings together through the wall with twine. (See external pinning.) The tubes will create a solid, superinsulated wall after the plaster is complete.
Image source: Home Hardware
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I really like this idea, but not the work of filling, stacking, and tamping bags of rice hulls. (not to mention stringing barb wire between the bag layers. I’m thinking of building a roundish house based on a timber frame barn-like structure. (Think of two concentric circles – 12 and 24 ft radius). The exterior wall (the 24 ft radius) would be built with wall trusses using dimensional lumber instead of solid timbers. Cover the inside and outside of the truss structure with geotextiles. Use a blower to fill the wall space with rice hulls. Spray interior and exterior with a lime mortar. Since the walls aren’t load bearing, I don’t think the rice hulls would need to be tamped, but maybe vibrated to increase settling. Instead of using rice hulls exclusively, use some mix of rice hulls, Rice hull ash, minerals, limestone tailings. Ideally mixed as a slurry that sets up an exothemic reaction that strengthens the wall?
I thought of something very similar about 10 years using poles instead of lumber. You’ll need to reinforce the mesh so it doesn’t bulge out. Use fine mesh so hulls don’t fall out. No vibrating needing — just rent an insulation blowing machine. There are numerous techniques of stabilizing the fill material if you want. See my Geopolymer House Blog and search for recipes and formulas.
http://geopolymerhouses.wordpress.com/
From my experience many areas wouldn’t allow a structural post to be set into the concrete like is shown in the drawing. Most building codes would require the post be set into a steel post base that was embedded in concrete. Most localities require the post base as a measure to prevent post rot. Of course pressure treated lumber would negate some of the rot potential. But usually the use of the post base is more economical then the cost of lumber treated for burial.
Keep in mind most of what we cover here is for areas with few or no building codes. The emphasis is on low cost/low tech. Anchors are great and that’s what’s typically used in code areas. I thought about mentioning that option, but decided to focus on the basics of working with rice hull bags. Trying to cover all the various options makes reading more difficult. The method shown assumes posts are wrapped in plastic sheeting so the wood is not in contact with the concrete.
I never recommend treated wood. Studies show it doesn’t last much longer than untreated wood, and there’s definitely adverse health and environmental affects.
Add a piece of plastic sheeting along the top of the tubes to protect the rice hulls in case of roof leaks.