‘Balecob’: Combine the Benefits of Straw Bale and Cob Building
Stem wall of urbanite and earthbag.
We live in exciting times in the world of natural building! In the grand scheme of things, the natural building movement is still in its infancy. While building with earth and sticks and such is ancient and global in application, its renaissance in the western world goes back only 30 or 40 years. And those 40 years of experience have been tempered by codes, regulations, and the river of twisted cultural values resulting in a slowly evolving field. But, it is growing like never before as people seek a greater sense of belonging in their homes and communities and look for a more authentic existence. With this growth, as with any new technology, natural builders continue to spawn innovations and creativity. Balecob is one such innovation whose time has come to be on the center stage.
There are many wonderful and inspiring books and websites out there that go into great detail about the quixotic nature of clay or the transcendental qualities of cob buildings and so on (check out housealive.org, for starters). With this article, however, I’ll start with the assumption that readers have a basic understanding of natural building.
What’s Balecob and Why Now?
What are the best inherent qualities of Cob? And what does a strawbale have going for it? How can they elegantly work together to give us beautiful, functional, soulfully wonderful homes? Balecob provides the answer.
There are things we come across in our day-to-day lives that intuitively make sense and help to create a new paradigm of understanding. Every child, for example, grasps the rightness of the ascendant seeds of a dandelion. I had similar feelings the first time I read Christopher Alexander’s timeless book, A Pattern Language. I found myself nodding my head in agreement to his design assertions page after page. It was this same feeling I got when I saw and learned about Balecob. And, as I describe it to others, they have the same nodding-of-the-head-in-agreement reaction.
Ianto Evans and the good folks at the Cob Cottage Company in Oregon came up with the original idea for Balecob. Ianto is the grandfather of the modern natural building movement and I gratefully tip my hat to the work he and the CCC have done for the past several decades. I learned Balecob from Coenraad Rogmans of House Alive and it’s a slightly different technique that I’ll explain forthwith.
Moving Past Wall Systems
Generally, when folks talk about the type of natural building they want they define it by what their walls will be. Like, “I’m building a…strawbale, cob, rammed earth, earthbag… house”. I encourage you to leave this type of limited thinking behind and instead focus on what materials will best meet your needs in a given wall or section of your house and what you have available. Got a lot of windows and doors on the south side? Consider framing it with wood. Have a long, cold north wall with no windows? Go with balecob or strawbale. Want curves? Use cob. Lack clay? Consider earthbags. Got cordwood up to your elbows? Cordwood-cob might be part of the answer. Interior walls could be light straw clay, etc.
By defining your home as a “natural building” instead you’ll put yourself in a new framework that opens more possibilities for a better overall building and building process.
Cob and Strawbale Attributes
Cob and strawbales are both great…for some things.
• Cob is strong and durable: it holds up roofs, it can last for centuries, it will stop runaway cars
• Cob is malleable: it can be shaped into curves, domes, and whatever (think clay)
• Cob provides thermal mass: cob stores heat and heat moves through cob slowly (~1”/hour) thus moderating temperatures in a building
• Cob is local and cheap: most of the material can usually be gotten from under your feet or just down the road
• Cob is good for you: just earth; no solvents, glues, paints, nasty stuff that makes your hair fall out or sperm count decline
• Cob is for the people (Democratic Building): anyone can do it!
• Cob is a great teacher: it is self-correcting in the sense that, as you experiment, cracks and crumbling will let you know you have room for improvement
• Cob is a poor insulator
Cob lends itself to community building
Most strawbales to be had in the U.S. are wheat straw. They generally come in two sizes: the larger three-string bale of about 48” x 24” x 16” or the smaller, two-string variety: 36” x 18” x 14”(see pic). Check on sizes and availability well before you begin construction so you can plan the dimensions of your structure accordingly.
Strawbales are good insulators. They provide an R-value of about 2 per inch. For reference, conventional fiberglass insulation has an R-value of about 3.5/inch. With conventional strawbale construction that sets the bales wide-side down, total R values are about 48, much higher than code calling for R-13 or R-20 on walls. This is great but also a bit of overkill that has merely been a function of bale size (note: we’ll explain later how Balecob sets bales on their narrow side. Think to yourself why this is a good idea and give yourself a star if you turn out to be on track).
Strawbales take up a lot of space. Whereas cobbing a wall can seem excruciatingly slow going as it rises inch by sluggish inch, plopping a row of bales on a wall leaves one feeling downright effervescent! Of course, it’s never as straightforward as that and there’s always more work to be done with bales but volume is volume.
Strawbales are structurally weak (load-bearing strawbale houses, for example, make use of a lot of wood and wire to provide structural support and shear strength).
In conclusion: use cob for strength, mass, and curves; use strawbales for volume and insulation
The foundation has two parts: the rubble trench and the stem wall. Rubble trenches are an age-old technology that always impress me with their simple effectiveness. A well-built rubble trench does two things very well: Moves water quickly away from a building keeping the above-ground materials dry; eliminates any chance of frost heave
Conventional concrete foundations must be set below the frost line (often 4’ or more) because they are solid and will heave if water freezes and expands under them. Rubble trenches do not have to extend below the frost line because if water does pool and freeze in the trench it has room to expand between the gaps and will not heave the walls. How deep you make yours is a function of the annual rainfall your area receives.
Next comes the stem wall which also does two things: Raises the cob and bales above the ground keeping them away from water; provides a solid base on which to build walls
Stem walls can be made from many materials including stone, brick, urbanite or earthbags. One could also pour concrete but their natural building Karma will suffer. Whatever material you use, center your stem wall over the rubble trench and be sure to make it about three to four inches wider than your bales’ width (narrow-side).
The height of your stem wall will depend on your conditions and materials available. If you get lots of rain and it is often driving, then higher is better especially on the windward side. If you have access to lots of great stone or urbanite, you might choose to make it higher thus reducing the need for bales and cob.
The Bottom Bead of Cob
Once your stem wall is up and mostly level, paint it or sponge it with some clay slip and start building a layer of cob about 8” to 10” high. Fill in any gaps and spaces in your stem wall as you go so you can have a more level surface on which to stack your first row of bales. Some sections may only be 6” while others are 12”. That’s ok as long as this cob bead is helping to make the base level. Re-apply slip to the wall as needed so it is wet when you lay on the cob. This layer of cob should match the width of the stem wall and will tie in the separate components of your stem wall creating a very strong foundation.
When the cob bead is still soft and wet, coat a bale with slip on all sides. You can scoop slip onto the bale and rub it into the straw (put a tarp underneath) or dunk the bale in a flat of slip a few inches deep. The idea is to coat the straw thoroughly so future layers of cob will adhere strongly to the bale. Without the slip, any cob smushed against the bale will likely fall off. Think of slip as primer.
Set each bale on its narrow end so they are centered on the cob bead. This should leave a couple inches of exposed bead on either side of the bales. That’s good because it will be the base upon which we’ll eventually apply more cob to the sides and the finish earthen plaster. We set the bales on their narrow sides because we can save space on our footprint and foundation and use fewer bales while still getting an R-value of about 32 which, for walls, is outstanding. The one downside is that the broad side of a strawbale has the straw running lengthwise which is harder to stick plaster to which makes slipping it even more important. I feel, however, that this disadvantage is far outweighed by the advantages.
When designing your building in the beginning take time to plan out your wall lengths and heights with consideration for the sizes of your bales, the widths of the cob columns, the height of the bottom bead, and the top bead of cob that will support the roof. Plan to use half-bales for the start of each successive start.
For each Balecob wall we build there will be two or more cob columns as high as the walls providing much of the structural support to hold up the roof. For a short wall of ten feet or less, there need be only one column at each end of 8” – 12” wide by the width of the bale. For larger spans, an additional column in the middle will be necessary. On a house with 30’ walls we built in South Dakota, we built three cob columns (two ends and the middle) each two feet wide. This left 24’ for bale infill – or three bales on each side (either 3 full bales or 2 full with 2 halves).
Cob Base Coat
As each slipped strawbale is added to the wall, cover it all over with a one to two inch layer of cob. This means the sides, ends, and the top. Then, set the next bale right against the first. There will always be gaps between bales so really cram the cob into these cavities. This encases each bale in cob and one can start to imagine how strong the wall and structure will be as the cob forms a lattice of strength over, under, and between each bale. Add to this the cob columns and the top and bottom beads and a strong wall will be had!
Upper Cob Bead
After the last row of bales is stacked and set it’s time to lay the upper bead of cob. Make this bead about 10” thick for larger structures (on my pig house I went about 4”) and use the natural malleability of cob to level out any rises and depressions in the bale wall so that the top plate and roof beams will lie true. This bead will connect the cob columns to the cob base coat to the lattice between the bales to the lower bead like a python hugging a chubby kid (or a Capybara, a giant South American rodent).
Connecting the Roof to the Walls
It’s very important to connect your roof with the mass of the wall to ensure a solid and strong building. We use “dead men” and metal strapping for this purpose. A dead man, in Natural Building parlance, is a hunk of wood (dimensional or not) set into a cob wall and then surrounded by cob that serves as an uber-strong anchor for shelves, stairs, benches and, for our purposes right now, to securely attach roofs to a wall.
In straight-up cob construction, we set metal strapping with deadmen all along and into the cob walls 16” or more from the top of the wall. This provides a super-strong anchor to tie to the bottom plate or beams of the roof structure. There are several ways to roof a cob building but that is beyond the scope of this article.
With Balecob we use similar methods: dead men and metal strapping in the cob columns as well as under the top bead and under some of the top-most bales every couple feet (this will vary based on your roof type). Over the length of a wall this gives numerous, well-anchored attachment points.
Windows and Doors, Electric, Plumbing…
Fear not, with Balecob, all of these can be incorporated into your building but this is, once again, outside the scope of this article. Do your research, take a workshop with us, play around with the materials and you’ll get ‘er done and wind up with a beautiful and highly functional building.
All photos courtesy of Conrad Rogmans
Kyle Chandler-Isacksen runs the Be the Change Project with his wife in Reno, Nevada. They are dedicated to creating a just and life-sustaining world while having fun doing it. They were one of MOTHER EARTH NEWS’ Homesteads of the Year in 2013. Shoot him an email, and read all of his blog postshere.
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