Light clay/lime straw insulation bats brainstorm--thoughts?

I apologize in advance if I overlook any funny typos or malapropisms.  I'm living in a bilingual situation and it's doing funny things to my grammar and word recall!

We've recently moved into our wattle and daub house.  We live in a moderate equatorial mountain climate; our seasons vary between rainy and sunny with the coldest being some nights around 30 F and hottest days maybe 75 F.

The roof is corrugated tin, hip style, almost 1:1 so when finished we'll have a pretty spacious attic--almost another floor but no windows.

We're used to much colder temperatures than what is usually tolerated in the States with central heating.  However! We would like to warm things up so we can stop waking up in the morning to a 48 degree room.  We look forward to building a rocket mass heater, etc.  But for now, first things first: stopping the heat of the day from escaping straight through the roof after nightfall.

We'll soon floor the attic, which will create a bit of a stop gap, for starters, but we want to insulate the roof itself.  I want to attempt to make my own grass insulation bats.

We'll build a simple wood form about 6" deep and lay it down on sacking material  We'll make a light clay straw mixture, and I think I'd like to add lime, with the thought of its resistance or repellant nature toward fungus and insects.  Pack that into the form and let it dry in the sun.  I'll find out if this product holds together and how much it ends up weighing.  If it works, we will have a natural and practically free insulation bat that we can secure between the rafters.  What I don't know is if this will turn out to weigh a ton, or be really brittle, or some other totally unforeseen concern.  In my online searches, I find commercially produced insulation made of hemp or grass, but I have not found a DIY on that.  Thoughts welcome-- I'll try to follow up with the results of my experiment.

I would be concerned it would create a rodent habitat. Without a vapor barrier it may attract and hold water. Would the clay make it fire proof? In the event of a fire would bits of grass rain down as burning embers?

THOSE are what come to mind; but am unfamiliar with these materials so unsure if any of these concerns would affect the project. Good luck.

From an old thread recently resurrected (https://permies.com/t/54793/Straw-clay-attic-insulation), light straw-clay runs in the neighborhood of 13 pounds per cubic foot (5-10 times as much as conventional insulation materials), so you would need to investigate whether your roof framing will support as much as you want. Probably for the mild climate, 6" would be enough, so say 7 psf. What is the roof framing - sizes and spacing and span from ridge to wall?