Foundation Bale Junction

Your foundation serves the purpose of supporting your building and all the loads imposed on it. Remember in the detailing phase that all those loads are transmitted through the bale walls and into the foundation. This means that the entire bale wall and the plaster skins

12.1a - b: These are good basic wall sections. 1a shows a load-bearing wall on slab foundation with a framed roof. 1b shows a load-bearing wall on a perimeter wall or pier foundation with a truss roof. The arrowed lines show the path of the precompression wires. Notice the top plate bearing on the plaster and the plaster bearing on the foundation, with a flashing to protect the seam at the bottom. This kind of generous (24 inch minimum) roof overhang is a must.

12.2a: Rubble trench
12.2b: Slab detail (with hoses)

(which carry most of the loads) must be able to bear on the foundation dir-ectly (or indirectly, if the load path is appropriate).

There are many ways to successfully create a good junction between your foundation and your bales. The main points to be remembered are:

Damp proofing. Both the wood and straw elements you place on your foundation are the most prone to rot due to moisture damage. Some kind of isolation strategy must be in place, which could include foam sill gaskets, poly vapor barriers, asphalt paint, tar paper, or any other long-lasting, waterproof material. Use wood species like cedar that are naturally more resistant to moisture damage. If you must use pressure-treated lumber, be aware that some types are more toxic than others.

Elevation above grade. Your foundation material is capable of handling sub-grade and at-grade moisture and exposure;your

12.2c: Slab detail (under curb)






12.2c: Slab detail (under curb)

12.2d: Pier detail

12.2a - d: The same kind of thinking goes into bale/foundation junctions regardless of the kind of foundation being used. Bale curbs elevate the bales from the floor height, a base flashing keeps the seam dry, and both plaster skins bear on the foundation.

walls are not. Make sure any wood and straw are at least 12 inches above the finished grade.

• Curbs or toe-ups. These wooden runners serve several purposes: they help to elevate the bales above the finished floor level, in case of interior flooding; they provide attachment points for mesh, flashing, and trim; they provide guides for placing the first course of bales; they provide a channel under the wall for routing wiring; and they are good plaster stops.

• Flashing. The base of a wall is where all the rain running down the wall will accumulate. A flashing strategy must be employed to ensure that this moisture cannot end up running or wicking under the wall.

• Anchor points. The wooden curb rails must be anchored to the foundation, as do any posts and rough framing bucks. For load-bearing walls, the compression system for the bale walls also needs an attachment point or a route through the foundation.

• Insulation strategy. A great deal of your heating energy can be lost if your foundation is not properly insulated. Take care to prevent all thermal bridging at this critical junction, both above and below grade. If you can successfully integrate all of these considerations into a foundation detail, then it will serve its purpose.

• Cantilevered floors. A wooden floor system can be cantilevered past the edge of the foundation wall or beam so that the bales are centered over the foundation wall. This allows for a bit more room on the floor of the house without requiring a larger foundation footprint.

Bale Curbs

The bale curbs (also known as toe-ups) consist of two pieces of wood spaced apart to match the width of the bales. We use them on every type of foundation because they serve so many useful purposes. How you place these curbs will help to determine the final finish of the walls and will have implications at many stages in the bale raising. Here are some guidelines for curb design details in your plans.


Make sure your curb rails reflect the real-world dimensions of your bales. Many designs assume a certain standard dimension for bales, but not all bales match these standards. Since a difference in spacing of an inch or two will make a big difference during construction and plaster-ing,know the accurate bale dimensions prior to creating the detail drawings, and ensure that the drawings reflect these dimensions. It may be more difficult to draw a 19-inch spacing than a more even 18 inches, but it will save many hours on the jobsite if it's drawn properly in the first place. There are many ways to space the curb rails, and each will result in a different finish:

• Directly in line with bales. It is common to arrange the curbs so they are directly aligned with the inside and outside faces of the bales. In this case, the interior plaster will cover the wooden rail and finish directly on the floor. The exterior plaster will also cover the wood, and in this case it is very important that the curb rail be set back from the edge of the foundation by % to 1 inch, so that the plaster skin is bearing on the foundation, not overhanging it. Overhanging plaster is not able to transmit loads to the foundation directly, resulting in a wall that is not as strong.

• Set wider than the bales. The inside, outside, or both curb rails can be set % to 1-inch wider than the bales. In this scenario, the plaster will finish on top of the rail,leaving the face of the wood exposed. The wood then acts as a finishing line for the plaster, and the exposed wood can be used to attach trim after plastering.

• Overhanging the foundation. The outside curb rail can extend beyond the edge of the foundation, and with a bevel cut on the top and a drip kerf grooved into the bottom, it can be part of the flashing strategy. In this scenario, the wood must be properly treated to handle exposure to the weather, and the plaster must bear on this wood such that loads are still traveling into the foundation. This usually involves a rail of wider dimensions (2-by-6 or greater).


The most common curb rails are 2-by-3s or 2-by-4s laid on their flat side, providing a toe-up of 1.5 inches. If more height from the foundation is required, these rails can be placed on their edges, and larger dimensions of lumber can be used. In such cases, blocking should be run between the rails at regular intervals to tie them together, where compression wires will be run in load-bearing buildings.

In areas with seismic activity, the curb rails are typically larger in dimension, from 4-by-4 to 6-by-6. These become part of


12.3a - b: Above, the curb rails are spaced to allow the plaster to bear directly on the foundation/floor. below, the curb is set wider to allow the plaster to finish on top of the wood, leaving a nailing face exposed for trim. The curb could also be outset on the outside edge, depending on the flashing detail.

12.4a the strategy to ensure the wall maintains its integrity under earthquake conditions.


Insulation materials to be used between curb rails should ideally combine three key properties: impervious to moisture, well-draining, and rigid. It is common to use rigid foam insulation here, but it does not allow for good drainage should water enter the wall. Pea gravel is also used, but it doesn't offer much insulating value. The best insulations are vermiculite, pumice stone, or foam balls. Drainboard insulations can also be used, but their effectiveness at draining is much poorer when used horizontally.

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