Need advice on cob filled pallet house with sawdust insulation

Hey permies,
  I need advice on a plan I have to build a pallet house. I plan on maybe 4 inch posts set the width of  a pallet and to screw the pallets to each side of the post to make up an interior and exterior wall. Then fill each side with cob and the middle 4 inch void filled with sawdust lime and borax.
 Does this seem viable or will the sawdust absorb  too much humidity? They use it on cobwood right?
Also plan on an earth roof with woodchips instead of earth, why do people not use woodchips on an earth roof,or at least I haven't heard of it?
Also I may just cut the boards off the pallets and use as lathe's with about 2 inches of cob plastered on each side of the wall.
I'm kinda new to this kinda stuff, I built a couple of cob ovens that work great, but any input would be greatly appreciated.

Howdy William, sort of like this?

Miles, yes and no. There will be two pallets thick wiith a 4 inch space between the pallets that will be filles with lime ans sawdust. Or Maybe I'll just cut up the pallets and use the boards as slats and cover with cob. Do you see any problem with this method? Its kinda like a regular stud frame only larger with sawdust in the middle.