Straw bale walls are built in one of two ways: load-bearing, where the bales themselves carry the roof and the wall is limited to about 3 m high and 6 m between corners or buttresses, or post-and-beam infill, where a timber frame carries the roof and the bales only insulate. Infill is the better default after a collapse because it lets the roof go on before the bales and removes the height and size limits.
Part of Straw Bale Construction
The wall system is the choice of what carries the roof: the bales (load-bearing) or a frame (infill).
The Question Is What Carries The Roof
The two systems differ in only one thing, what carries the roof.
| Load-bearing (Nebraska) | Post-and-beam infill | |
|---|---|---|
| Roof carried by | The bale walls | A timber or steel frame |
| Wall height | About 3 m | Not limited by the bales |
| Spans | About 6 m between corners or buttresses | Not limited by the bales |
| Roof weight | Must be light | Any the frame can carry |
| Timber needed | Little | Much more |
| Bales protected during build | Not until the roof is on | Yes, roof goes first |
The details are in Load-Bearing (Nebraska) Style and Post-and-Beam Infill. Both rely on the same bale preparation and stacking, in Bale Preparation and Stacking.
What You Need
- A decision on building size and available timber.
- A foundation and stem wall; see Foundations and Stem Walls.
- Dry bales and a way to keep rain off them.
Method: Choose By Size, Timber And Weather
Step 1: Is the building small, one storey and lightly roofed? Then load-bearing can work. Houses up to about 60 m², workshops and storage buildings suit it.
Step 2: Do you need more than one storey, a heavy roof or large openings? Then use infill.
Step 3: Is wet weather likely while you build? Infill is better, because the frame can carry the roof first and the bales go in under cover.
Step 4: Is timber scarce? Load-bearing uses much less.
Common Mistakes
- Load-bearing with a heavy roof. The bales compress too far.
- Infill without protecting bales from rain until the roof is on.
- Mixing the systems carelessly, with posts that carry part of the roof and bales that carry the rest.
Safety
Unbraced walls and wet bales
A partly built bale wall is tall and unstable. Brace it against wind until the top plate is on, and keep fire sources away from stacked bales, because a loose bale burns readily.
What’s Next
- Learn next: Load-Bearing (Nebraska) Style
- Combine with: Post and Beam Construction