Eric,The tests done by John Zang in Australia show that about 4% compression of total wall height is required. This will not solve the differential settlement of SB walls and the window frames. SB walls with earth plaster will always display a certain percentage of creep over time, much more so then vertical wood posts. At present we have very little idea how much creep besides that it is not much. Reports vary from 50mm to less then discernible. Where a few mm is the most common. I suppose 50mm takes place where insufficient pre-compression has been applied.
Besides the above I would seriously recommend you to reconsider the use of threaded bar to pre-compress the straw bales and use packing straps instead. The threaded bar is a real pain in the neck and it also creates a condensation point right in the middle of the bales. In most cases where SB walls have been taken down revealing the central pins show decomposing straw around the all thread specifically in the bottom bales. The condensate trickles down the all thread.
Rene On Jun 3, 2006, at 12:03, strawbale-request@amper....muni.cz wrote:
Hi guys Interesting thoughts.We are considering a straw bale wall for approx 50% of the external wallwith the other 50% made up of glass. We have identified the issue of differential settlement and considered pre compressing the straw bale walls. Essentially we would have threaded bar inside the bales (2 per bale). These would be fixed to the sole plate and the wall plate would be tightened down to compress the bales. Thus taking out the initial compression. Do you know of any figures (rule of thumb) to apply to the compressive nature of the bales. The roof would be supported by both glass and straw bale walls. Cheers Eric Larmett Senior Engineer