Cob: Stone foundations, tree roots

[Kerry S Tebbetts]

Well, I've been trying to dig up some info about this.  This is more
complicated than I originally thought.  There are so many factors that
can influence the stability of both your foundation and the surrounding
trees.  Some of the variables involved are:  soil composition and
moisture, proximity to the tree's root zone, soil load capacity, water
table, etc.  It's almost enough to make my head spin.  I now have a basic
understanding of some of the factors involved, but no understanding of
how to apply it.  For example, what's *my* soil load, water table, soil
composition, tree root zone, etc.  Root systems vary from species to
species and also from region to region even within the same species.  

Anyway, I did find one possibly useful tidbit.  It seems to be
recommended that you should dig your trenches the larger of:  6ft away
from the tree or 1' for every 1" diameter of the tree at chest height
(one article specified the height to be 4.5ft).  This helps prevent the
tree from dying (if 1/4 of the root system is destroyed, the tree will
most likely die) and the roots from threatening the structural integrity
of the foundation.  

However, as I sit back scratching my head, I wonder how with so many
complicated variables someone came up with that generalized figure. 
After all, they say the root system can extend laterally 2-3 times the
drip line.  Also, the tree is going to grow bigger, right?  So digging
your trenches 14ft from a 14in diameter tree won't help much when the
diameter of that tree is 24in.  

I wonder, would a small cob cottage be stable above the ground on an
earthbag foundation? 

Another thing was recommended regarding digging drainage trenches.  When
they have to be done near trees , you should excavate by hand and tunnel
around roots that are larger than 1in in diameter leaving them intact.  

For those of you who have been involved in cob workshops or have seen
many cob houses, have you ever seen any nestled snugly in a wooded area?