Bales on Edge vs. Laid Flat

There are 2 main ways that I design straw bale walls.  They both have their advantages and disadvantages.  I will go over both of them so you can make a decision.

BALES ON EDGE

This is overall the easier way to build, and is the preferred method by my engineer.  The dimension of the bale laid on edge is about 14” or 15” making your wall a few inches thinner than bales laid flat.  To build, you begin with your bottom plate or toe ups.  You can use 4x4 or 2x4 toe ups depending on your seismic zone.  From there, your posts consist of ladder trusses, aka Larsen trusses, LVLs, or I-joists.  These are place strategically along the wall and also where door and window openings occur.  Then you have a box beam as your top plate, that wraps your whole perimeter.  See images:

Larsen Truss or I-joist posts with box beam top

Beginning to stack straw bales within Larsen truss or I-joist cavities

The bales are then laid on edge between the trusses in a running bond.  This eliminates the need to notch the bales around all of the embedded posts.  It is good to have the spacing between these trusses correspond with the bale lengths to minimize resizing of the bales.  So each cavity including above and below the window openings is filled with bales.  Then you add 14ga welded wire mesh to the interior and exterior face of the bale wall.  In extreme seismic zones, X bracing may be added to increase the lateral shear strength of the wall. 

Advantages:

·       Easier to build

·       Cheaper materials (2x4, OSB, I-joists)

·       Increased interior square footage

·       No need for notching bales

·       Fewer bales needed

·       Plaster skins take care of lateral loads

Disadvantages:

·       More difficult to plaster on bale face

·       Exposed strings makes niches difficult

·       You cannot weedwack the wall to smooth it out

BALES LAID FLAT

This is how the majority of my projects have been designed, mainly because Andrew Morrison and I have been doing it this way for almost 20 years.  This is a very solid way of building with bales, and has many advantages.  I think the main disadvantage is that it may be more labor intensive.  The bales laid flat are about 18” thick so you will end up with a thicker wall than if they were laid on edge.  To build, you start with the toe ups or sill plate same as above.  From there, the posts are 4x4s and the window and door framing.  The top plate is a 4x10 to carry the roof loads.  The larger top plate beam allows you to have large window openings beneath and larger spans between openings or posts.   The bales are then laid flat in a running bond for the length of the wall and notched flush around any posts or framing.  See Images:

Bales notched around 4x4 posts and door and window framing

Framed structure prior to notching and stacking bales

Advantages:

·       More design options for windows

·       Easy to plaster on bale surface

·       Sturdier and naturally stable

·       Frames up faster than other option

·       Eliminates thermal bridging

Disadvantages:

·       Decreased interior square footage

·       Labor intensive with notching

·       Larger lumber members (4x10. 4x4, 4x6)

·       Overall more expensive to build