Cob: Rubble Trench Foundation

[Spencer Perlman]

Howdy,

We are getting ready to start excavation for a rubble trench foundation for 
our straw-bale/cob home.  We have never built a rubble trench foundation 
before, so naturally we have a few questions.  Given that we are using 3 
string bales laid flat (23" wide) for the straw walls, how wide should our 
footing be?  Perhaps I should mention that the stem wall will be constructed 
from 8"x8" rail road ties.

Should the rubble be tamped or is compaction a non issue with this sort of 
foundation?  Also, we are considering putting a drain at the bottom of the 
footing, any suggestions for this task (materials, methods?)
Is it necessary to put vertical rebar from the foundation into the first 
course of bales?  If so, how should this be done with a RTF?

We want to mechanically compress the walls so we can plaster quickly after 
the roof is up.  Any ideas for securring the tie down system to the 
foundation?  Should the tie down start under the rubble or under the ties?

Thanks,

Spence
Arizona

ps, sorry for the cross post

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