[Cob] moss as roof insulation?

[Alex MacKenzie]

We have a relatively minimal amount of space with which to insulate the roof on our cob house, basically the gap found in a pallette -4 inches or so. These are held up by rafters which we would like to keep exposed on the underside. Yeah, it’s not a lot to work with, this we know.

We are really trying to work with local materials as much as possible, and besides our tin roof (for water collection), everything is either cob, wood, or old craigslist windows (with the potential to be double paned in the future - we have set aside matching windows all around).

So the question is what to insulate the ceiling with? 

We are leaning toward moss, as it is extremely plentiful, available on our land, renewable, and pretty fluffy stuff. We are on the top of a mountain on an island, so getting stuff up here is a pain.

I want to stress that we have about 30 acres of moss, so we won’t run out, and we won’t do any lasting damage by selectively picking it. We care about the moss!

We would look into fire retardants as well as some anti-vermin cover (borax, boric acid?).
The roof is already on, so we are insulating from below.
We would likely lift the moss up off the ground in large chunks, let it dry, and stuff it between the palette boards, likely stapling lumber wrap to the underside to keep it all in. We are then finishing with thin boards to cover the bottom of the palettes.
On the upper side is the top of the palette wood, followed (and going upwards) by waterproof roof tarp, then a gap where air can circulate (a raised and very sturdy lumber support) and then the tin finish.

Any thoughts, recommendations or past experience very much appreciated!
 
Some of our initial concerns/unknowns: absorbency, vermin, effectiveness.

Pics to give you context of the structure and environment can be found here: 
http://s263.photobucket.com/user/alexmackenzie/media/alexhouse.jpg.html <http://s263.photobucket.com/user/alexmackenzie/media/alexhouse.jpg.html>

Thanks!
Alex