In a load-bearing (Nebraska) straw bale wall the bales carry the roof with no frame, within limits of about 3 m wall height and about 6 m between corners or buttresses, under a light roof. The wall must stand under the roof plate’s weight for 2-4 weeks to compress before it is plastered, and the plate is strapped down to anchors in the stem wall.
Part of Straw Bale Construction
Load-bearing straw bale construction stacks bales into walls that support the roof directly, the original method from Nebraska.
No Frame, So The Limits Come From The Bales
Without a frame, the bales and the plaster skin that will later stiffen them carry everything. That keeps the building simple and cheap in timber, and limits it to small, one-storey buildings with a light roof. The parent article lists the limits: maximum wall height about 3 m, maximum unsupported wall length about 6 m between corners or buttresses, a roof of thatch, metal sheeting or light timber framing, and no multi-storey buildings. It suits houses up to about 60 m², workshops and storage buildings.
What You Need
- A dry stem wall and a moisture barrier; see Foundations and Stem Walls.
- Tight, dry bales; see Bale Selection and Testing.
- A continuous top plate, a doubled 2 x 6 or equivalent heavy timber beam, to spread the roof load across the bales.
- Tensioned wire or polyester strapping, and anchors in the stem wall.
- Pins; see Pinning and Strapping Methods.
- A light roof. See Thatching and Roof Systems.
Method: Stack, Cap, Strap, Wait
Step 1: Stack bales in running bond on the stem wall, pinning them as you go.
Step 2: Check the height against the limit; see the arithmetic below.
Step 3: Lay the top plate continuously on the top course.
Step 4: Strap the plate down with tensioned wire or polyester strapping that runs over the plate and through the wall to anchors in the stem wall.
Step 5: Add the light roof, so the plate and roof weight compress the wall.
Step 6: Wait 2-4 weeks before plastering, and check the strap tension as the wall settles.
Worked Example
The parent article gives about 3 m as 6-7 courses. A standard two-string bale is about 90 x 45 x 35 cm, so the course height depends on how the bale lies.
- Laid flat (35 cm high): 6 courses = 6 x 35 = 210 cm, 7 courses = 7 x 35 = 245 cm.
- Stood on edge (45 cm high): 6 courses = 6 x 45 = 270 cm, 7 courses = 7 x 45 = 315 cm.
So 6-7 courses reach about 3 m only with bales on edge. For bales laid flat, about 3 m would be 3.0 m / 0.35 m = 8.6 courses, between 8 and 9. Count the courses for your own bale orientation and measure the actual height; do not rely on the course count alone. The height from the stem wall to the top plate is what the 3 m limit refers to.
Common Mistakes
- Heavy roof on load-bearing walls. It over-compresses the bales.
- Plastering before the wall has settled. Settling cracks the plaster.
- Unrestrained top plate. Wind lifts or slides it.
- Walls longer than the unsupported limit. Add a buttress or a corner.
Safety
Tall bale walls fall over
A load-bearing wall is unstable until the plate is strapped and the roof on. Brace it against wind, keep people out of its fall zone while stacking, and keep sparks and flames away from loose bales.
What’s Next
- Learn next: Pinning and Strapping Methods
- Combine with: Plastering and Finishing