Rice Hull House Wall Section

Rice hull house wall section (click to enlarge)

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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More Choices for Insulated Earthbag Houses

Hart house in Colorado made with scoria-filled earthbags

There are lots of options for building insulated earthbag houses. At this time, scoria and pumice are my favorite. These materials are fireproof, rot proof, easy to work with, don’t attract pests, lightweight, etc. Kelly Hart pioneered the use of scoria bags in his dome home and carriage house in Colorado, and in my opinion this method deserves much more attention.

My Instructable above describes numerous ways for building insulated earthbag homes, and we keep learning more good options:
Foam glass gravel
Expanded clay granules
Foamy geopolymer with perlite
Lightweight geopolymer
Perlite Roundhouses
Rice Hull Earthbag House (make sure to keep the rice hulls dry or they will rot)
Solar Pit House (uses recycled polystyrene)

Good examples of insulated earthbag houses:
Half Moon Earthbag Earthship
Northern New Mexico House
Earthbag Scoria Casita

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Earthbag Scoria Casita

Here’s another great project. This small domicile demonstrates how scoria homes are faster and easier to build than bags filled with soil, and more insulating. This doesn’t mean standard soil-filled earthbags are obsolete. There are pros and cons to each system, however, I strongly encourage using scoria bags (or pumice or other suitable lightweight fill material) if there’s an affordable supply. Thanks to Joe for taking the time to document everything and share what you’ve learned.

“Hi Owen. Wanted to let you know I just uploaded 10 new videos on my YouTube site. One is a portable solar water pump, all others are on our earthbag building.

I’ve been keeping close track of our labor and expenses. We’ve only been able to work on the building for 5-7 days at a time, several times a year so it seems to be taking a very long time. However, I added up our hours so far and was pleasantly surprised. To get to our 8′ height, ready for the bond beam, including digging the foundation, laying bags, framing and providing lintels for several windows / door openings, putting in a main beam with floor joists for loft:
392 RUNNING TOTAL HOURS
392 hours is only 9.8 40 hour weeks. If you could extrapolate this to a crew of 4 this would be about 2 ½ weeks!!!

Thanks once again for your advice, and thanks to you and Kelly for keeping up your wonderful earthbag sites. Feel free to use this info.”
Joe

You can watch all his videos at Festimr’s Channel. (Required viewing for serious earthbaggers.)

Related:
Using Scoria for Earthbag Building (Good overview of the benefits of using scoria or pumice.)

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Another Insulated Earthbag Method

This new insulated earthbag idea is from Chris, one of our readers.

“Feel free to post away with the idea–after all, ideas are to be shared not owned. It seems like a good way to efficiently build thermal mass inside insulation, while being another (simpler? faster?) alternative to compartmentalized-sewn bags or laying inner and outer bags. Hopefully your readers can bounce it around and maybe think of some efficient method/uses for a separated fill earthbag idea.

I am thinking more insulation than thermal mass for the wide temperature range of my mountain environment, and naturally favored a scoria route for a while. After thinking about cast stone/scoria EB and the history of pumicecrete, I wondered if a division similar to eternally solar EB would be better, with thermal cast stone inside and scoria outside. It would seem simple enough to place a ‘divider’ in the bag when filling one side with cast stone or any thermal mass and one side with insulation and then pull the divider, close and tamp as normal. I’m thinking maybe the lower half of the dome would be more appropriate than the corbelled upper part wherein the weight would be hanging inside the previous layer while only leaving lightweight insulation above previous layer…

It seems that separating thermal mass and insulation would be more effective than one insulative pumicecrete type fill (no experience there though). And if so, the divider in the bag while filling seems easier than sewing a divider in a bag, laying two separate bags, or spreading a thick layer of thermal mass on the inner plaster…”

Owen: Great idea. I think you’re onto something. Previously, I thought a temporary divider for filling bags would be cumbersome and cause a lot of the material to get mixed together. But the way you explain it, it sounds very do-able. I hope you can make at least one sample and send me some documentation of your results. High resolution pics are preferred. If it works, I’ll put it on the blog and maybe the next (2nd) earthbag book if that’s okay with you.

Owen’s thoughts:
– You can adjust the ratio of materials to match your climate (more insulation in cold areas, less in milder climates).
– Scoria’s R-value is not real high so probably better to add extra
– It doesn’t take much thermal mass to create a flywheel effect. Thick plaster and insulated mass floors is typically sufficient. But you need to hold everything together with lots of twine, etc. You could leave out the geopolymer in the bag and use all scoria.
– Measure the quantity on each side so the walls stay level (ex: 1 bucket geopolymer, 3 buckets scoria, etc)
– The geopolymer will compact, but the insulation won’t (or very little). Add extra geopolymer to compensate.
– Add baling twine, especially on upper courses of scoria to tie everything together. This is shown in Kelly Hart’s free dome building guide.
– Clean 1/2″ scoria is preferred.

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Alternative Fill Materials for Eternally Solar Earthbags

We’ve been discussing the Eternally Solar earthbag building system at length. Engineering tests show their walls exceed building code requirements even when filled with sand. Their bags are also used to form lintels and bond beams.

As exciting and practical as this is, there’s a wide range of other options. Their earthbags can be filled with different materials for optimum performance in different climates. Simply choose low cost, locally available materials that are appropriate for your situation.

Option A for cool climates: 1. insulation in outer tubes, 2. clayey subsoil in the center (for stiffening the wall), 3. sand in the inside tube for thermal mass.

Option B for cold climates: 1. scoria, pumice or perlite in outer tubes, 2. clayey subsoil mixed with scoria, pumice or perlite in the center, 3. sand in the inside tube for thermal mass.

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Mesh Bags of Recycled Foam

Mesh Bags of Recycled Foam

Patti Stouter has been experimenting with all sorts of things, including using mesh bags of recycled foam. She wants to build a Nubian vault with these bags of foam on a rebar frame.

Scrap materials are often large enough to fit well in cheaper open weave vexar mesh tubes. This stretchy plastic tubing is used for onion bags, and makes firm rolls of scrap foam or packing peanuts 10”- 12” in diameter (25- 30 cm). Softer materials like strips of grocery bags can be fluffed and used as a cavity fill, but may require a sturdier mesh base for the plaster.

Note: test a sample bag before making large purchases to ensure they will work for your project.

Note: There’s lots of content on our websites about building insulated earthbag houses. Use the search function in the upper right of the page and search for terms such as insulated, cold climate, etc. Here’s one link on insulated earthbag houses.

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Condensation Problems in Cold Climates

Kelly Hart and I have been following the The Year of Mud cob house blog for about 2-3 years. Ziggy, the builder and author of the blog, learned the hard way that cob (actually, earth building in general) is not a good choice in cold climates.

Kelly has been warning people for years at GreenHomeBuilding.com (the number one most popular site on natural building) that some earth building techniques are not appropriate for cold climates. We also want to make sure our earthbag website readers are aware of the limitations of building with earth in cold climates.

Kelly has an interesting story about this on his website. He stayed in an old adobe hotel in southern Colorado one winter. It was freezing cold inside. Despite the thermal moderating effects of earth (the flywheel effect), if there’s extended freezing cold then the inside temperature can be like living in a cave, because earth is not a very good insulator. That’s why most adobe houses are built south of the Colorado/New Mexico border. That’s the range where colder temperatures start to make adobe impractical. The same is true with earthbags, unless the structure is insulated.

You can find much more on this topic on our websites by searching for “insulation”, “insulated earthbag” and “cold climate”. The key is to either fill the bags with insulation such as scoria or add a layer of insulation on the exterior.

Please note, we love Ziggy’s blog and encourage everyone to check his site regularly. He has lots of good ideas, and his open, sharing approach is conducive to learning.

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Instructable: How to Build an Insulated Earthbag House

Energy performance on most buildings can be improved with insulation, including those made of earth such as adobe and earthbag structures. Although most earthen structures are located in hot, dry climates, there is increasing demand for low-cost, eco-friendly earth building techniques in cold climates. This article explores four innovative methods for insulating earthbag buildings, which extends their building range to cold regions.

Most earthbag buildings use polypropylene grain bags or mesh bags filled with soil. Bags or tubes can be used. We demonstrate bags, because they’re often available recycled for very low cost. The bags or tubes are filled in level courses and then tamped solid. There are typically two strands of barbed wire between courses to bond the bags to each other and add tensile strength. The building process for insulated earthbag houses is nearly the same, although the materials would weigh significantly less and speed construction considerably.

Unlike other earth building methods, earthbag building has the unique advantage of providing either thermal mass or insulation, and therefore can be adapted for cold climates with an insulated fill material. Scoria, pumice, perlite, vermiculite or rice hulls are all suitable insulating materials. These materials are natural, lightweight, easy to work with and non-toxic. Most (all but rice hulls) will not burn or rot and do not attract insects or vermin. In addition, all but rice hulls are not adversely affected by moisture and can be used as part of earth-bermed or earth-sheltered structures. Recycled polystyrene (Styrofoam) is another good possibility. Another possibility is adding foam board or foam insulation on the exterior of earthbag walls, as explained in the 4th option.

You can read the entire How to Build an Insulated Earthbag House instructable by Owen Geiger for free.

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$220,000 Affordable Housing

$220,000 Quinhagak Prototype

Quinhagak Prototype Floorplan

I almost jumped out of my chair when I read about this ‘affordable housing’ project in Alaska. The estimated $220,000 cost for this home is “less than half of the cost of new homes recently built in the village.” It has 900 sq. ft. conditioned space, 1080 sq. ft. total. (That’s about $204/sq. ft.) I don’t know about you, but that doesn’t sound very affordable to me. Granted, the conditions are severe and building homes in areas like this is extremely challenging. In many cases everything has to be flown in or at least shipped long distances. But still, it seems possible to build for less than that using earthbags. I predict big advances in cold climate earthbag construction in the coming years.

I don’t have all the answers. I’m posting this project here to try to get people thinking of better solutions. We were talking about perlite houses not too long ago. Would an earth-bermed earthbag perlite house be practical to build in situations like this? It’s interesting to think about and could be very profitable. Whoever figures out simpler, more affordable housing solutions would likely be swamped with work. And in this housing market, that sounds pretty good.

Cold Climate Housing Research Center – Quinhagak Prototype

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How Much Wall Insulation Do I Need?

From time to time we answer reader’s questions.

Jeff: We are looking at building a home on acreage in central north Michigan. It is extremely cold in the wintertime where we are looking. Would an earthbag home insulated with rice hulls (using 10″ tube sandbags on exterior of earthbag walls) be sufficient for that kind of climate? How do you protect the lower courses of rice hulls from moisture from the ground to prevent rot?

Owen: Adding 10″ of insulation on the outside of walls should be plenty. That’s more insulation than 2×4 and 2×6 walls. At R-3 per inch, that’s about R-30 walls! (It’s probably less than that because of the shape of the tube, so let’s say R-25.) This will give you a superinsulated wall with a thick layer of thermal mass covered by a thick layer of exterior insulation. That’s ideal.

To protect the rice hulls, build a footer and fill lower tubes (or bags) with scoria or something that doesn’t rot. Use rice hulls once you’re above the level where moisture can cause problems. I have several articles on the Internet about building in cold climates such as this one: Insulated Earthbag Houses

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