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STRAW BALE ENGINEERING

Octagonal Pole Frame for large commons house with straw bale roof and 15’ tall straw bale walls. The building also received the first known Code approval for an earthen floor system. Several similar designs have been based upon this particular framing system.

Although we do not advocate the use of straw bales as a building or insulating material, we have nevertheless on many occasions provided engineering services for such structures.

Straw bale construction can be effective under the following conditions:

The plan is simple and the spans are not greater than about 20’ for 2 string bales.

The owner-builders are prepared to make a substantial investment of time, and often money. They should be familiar with applying multiple coats of plaster.

The workers are not already allergic to straw, and proper measures can be taken to limit any development of allergies.

The building is located in a relatively dry climate, and/or substantial measures are taken to prevent moisture intrusion into the bale stacks.

FINITE ELEMENT ANALYSIS OF OCTAGONAL POLE FRAME
USED IN LARGE STRAW BALE STRUCTURE

The FEA of the above pole framing system is shown here. Notice that as in many framed structures the stress is maximum at the foundation attachments.

These two pictures show the “reduced framing” method of straw bale construction; the door and window bucks are used structurally to stabilize the frame and to provide a tension path into the foundation using standard heavy hold-downs. This method achieves the lowest total cost for medium sized buildings. The nearly complete structure is shown below.

The above custom home utilizes double 2x walls (also known as “envelope construction) to create a cavity that is filled with blown-in insulation. This system has many advantages over typical straw bale construction as it equals or exceeds the insulation value, preserves the attractive deeply recessed window ledges, lowers total cost, and provides a much improved structural system. This method is highly recommended for high value construction where long structure life is a consideration.

Although we do not advocate the use of straw bales as a building or insulating material, we have nevertheless on many occasions provided engineering services for such structures.

Treehouse Engineering

P.O. Box 1571
Cave Junction, OR 97523
treehouseengineering@mac.com
http://treehouseengineering.com

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