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Posts Tagged ‘rice hull house’

Rice hull house wall section (click to enlarge)

Rice hull house wall section (click to enlarge)


Post caps secure the beam to tops of posts

Post caps secure the beam to tops of posts


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
(shop for low cost alternative brands of hardware)

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A cellulose insulation machine like this one could be used to blow rice hulls into earthbag tubes.

A cellulose insulation machine like this one could be used to blow rice hulls into earthbag tubes.


Cement mixers can greatly reduce labor and speed construction.

Cement mixers can greatly reduce labor and speed construction.


Posthole diggers (augers) can be used to dig holes for posts.

Posthole diggers (augers) can be used to dig holes for posts.


Mike, in Texas, has been asking some interesting questions about wrapping a post and beam frame with tubes of rice hulls. He thinks this is probably the fastest way to build an earthbag house. He may very well be right. Conversations and blog posts like this one are my favorite. Here’s part of my email reply to Mike.

Previously I reported on the rice hull house in Thailand that was a success. The owner has agreed to write a follow-up report soon that we’ll publish here when available. So we know rice hulls will work under certain conditions. The main issue is keeping the hulls dry.

Here are some suggestions for speeding construction. Note how all the machines could be rented so you don’t have to invest in a lot of expensive equipment. You could rent a cellulose machine (blower) and blow rice hulls through a hose into earthbag tubes. (Tubes are faster than bags.) This would take about one day like you said. But you have to figure out how to stabilize the tubes (hold them in a vertical plane and prevent from shifting around). I would put 4×4 posts or round poles about 3′-4′ apart to align with windows, doors and corners. A posthole auger would make quick work of digging holes. Build the roof before proceeding. Factory made trusses are fast and efficient. Now you’re ready to fill the tubes. Put the tubes on the outside of the posts and attach to backside of posts with baling twine. Put baling twine between tubes for later attachment of plaster mesh. Spray the walls with plaster using a mortar sprayer. Use wide roof overhangs and/or wrap-around porches so the rice hulls never get wet and so you can use earth plaster to save money. First 2-3 courses are gravel bags/tubes to prevent moisture problems. In Texas you could make the rubble trench flush with the ground and use just two courses of gravel bags/tubes. Post and beam with factory trusses and engineer’s stamp would enable bank financing, contractor sales, building permits and insurance if necessary.

Earthbag is super simple. But for those just starting out, my earthbag building book and DVD are now available. Everything is explained in great detail.

Below is a work schedule based on a modest sized home with experienced crew and mechanized system (cement mixer, truck to bring the sand and cement right where it’s needed, post hole auger, insulation blower):
Day 1: Dig trench and post holes, rough plumbing, fill trench with gravel, set posts in concrete
Day 2: Set beam, fill 2-3 courses of gravel bags (back truckload of gravel right next to work area)
Day 3: Set trusses, sheath roof, install metal roofing
Day 4:, Fill tubes with rice hulls
Day 5: Minor carpentry (windows, doors, interior walls), run electrical, attach mesh
Day 6, 7, 8: Spray plaster (move mixer and materials right where it’s needed)
Day 9: Earth floor (see blog post on 11 different earth floor methods)
Day 10: Ceiling, finish electrical and plumbing

Image source: Manifold Recording
Image source: Taylor Rental
Image source: Save My Gardening Tips
YouTube: Rice hulls are an excellent building material.

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I’ve had the pleasure of corresponding with Paul in Chiang Dao, a district north of Chiang Mai, Thailand. We’ve been discussing how to build an earthbag house with bags filled with rice hulls. Rice hulls are super cheap, fire resistant, superinsulating, and super lightweight and easy to work with. Rice hulls are the by-product of processing rice (the protective coating around the grain), so they’re 100% natural and sustainable.

I’m very happy to see others experimenting with alternative building techniques such as rice hulls. I can’t overemphasize enough how just one successful project could lead to many thousands of other structures. This could easily happen due to the extremely low cost and simplicity of construction. In our area, a half semi truckload of rice hulls cost about $25. Recycled bags for half price are widely available from farmers and feed stores.

A few details:
– lower courses of bags are filled with gravel, which sit on a rubble trench
– bags of rice hulls are less stable than tamped earth and so extra reinforcing is required (ex: rebar on each side of the wall tied tightly together). This could be added after every 4-5 courses so walls can’t shift.
– tie courses of bags together with twine for added stability (this also makes it easy to attach fishing net or plaster mesh if needed)
– protecting rice hulls from moisture damage is key, so plan accordingly. The privacy wall would benefit from a protective covering such as a cap of roofing tile.

The house is still a work in progress, but as you can see they’re making good progress. Notice how they’ve improvised here and there to add extra reinforcement. My main concern now is seeing the roof get built before the upcoming rainy season hits. Rice hulls can rot if they get wet, and they probably will get wet if there’s no roof or other protective covering.

Here’s some background information on rice hulls.

Paul’s rice hull wall photos on Flickr. (Hope he adds more in the future.)

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