Designing the Straw Bale Toe Up
In designing or building a straw bale wall, one of the most important issues is keeping water away from the bales. Large overhangs above the walls help to keep the water from reaching the bales from above. From below we utilize toe-ups. toe-up serves to elevate the bale wall above the floor where water can reach the bales and wick up into the straw from below. Typically two rows of pressure treated 2x4s, laid flat on the inside and outside face of the wall, have been nailed to the floor. Pea-gravel for drainage or rigid insulation is then filled into the space between the boards. The bales are then stacked upon the new toe-up.
Recently, the 2x4s have been replaced by 4x4s. From a designer’s standpoint, for a couple of reasons, I couldn’t agree more. First is purely for my ease of mind. The whole reason to install the toe-up is to protect the wall from water. And yes, I’m sure that 2×4 toe will probably serve this means, but when I look at a section of the wall it just looks so weak and like out of proportion. It is almost like looking two new porches. They’re basically the same porch except, one is built with 4×4 posts, and one is built with 6×6 posts.
Mathematically the 4x4s are more then sufficient to carry the loads, yet something about looking at them leaves an unsettling feeling deep in my mind. Is it strong enough? Subconsciously this could haunt you for some time. The larger members may be more than is needed but subconsciously you feel totally safe walking under it. So back to our toe-up, the 4x4s are larger and give your wall a greater, mind-easing and safer distance between the wall and floor. Second is for ease of full system construction. After the wall is raised the skins must be applied. Typically the mesh is attached from the top plate down to the toe-up.
With the new engineering calcs, the walls have been simplified, and the skins (mesh and plaster/stucco) act as the shear to carry the load of the roof. So it is very important that the mesh be solidly connected to the building. At the bottom with the 4×4, there is 3-1/2″ of meat to attach the mesh to instead of the mere 1-1/2″ with the 2×4. This will insure a stronger, tighter building. After the walls are meshed and plastered the interior finish may call for base board trim. Having sufficient backing (3-1/2″) to attach the trim board to, will give a higher quality of finish to the design and trust me, the finish carpenter will thank you for it.
So on your next project remember, it may cost a bit more, but realize all that is on the line with your project. Give your bales the clearance they deserve, after all they are protecting you from the elements, regulating the moisture and temperature, satisfying your environmental conscience, and of course inspiring you with their beauty.
ABOUT THE AUTHOR Chris Keefe, from an early age, discovered his creative spirit in art. In 1996, he received a B.A. in Liberal Arts focusing on drawing, Music and Philosophy from San Francisco State University. In tandem, he was actively involved in a grassroots environmental project for five years at the University of California in Berkeley. He became interested in the field of straw bale as he began his graduate studies in 1999 at the San Francisco Institute of Architecture. Focusing to integrate his work in the environmental and sustainability field with his creative imagination, he received a Master of Architecture and Ecological Design in 2001. Soon thereafter, he founded a company called Organicforms Design which offers ecologically and artistically based design utilizing natural and sustainable materials. Since then, he has worked and completed several exciting design/build projects in Southern Oregon. In 2002, he began to focus primarily on straw bale research and design as the lead designer on the innovative project, The Straw Bale Village in Jacksonville, OR. Please visit his website at www.OrganicFormsDesign.com
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