insulation help

Hello!  Need some help deciding on insulation for my new baby....
I had someone local use native cedar/juniper boards-siding build me a shed that I am converting to an office/work building.  

He put up a tyvek barrier, at first we weren't doing this, then somewhere it got added in.  Now I think I should remove it before I do the interior walls.
Any thoughts, will it trap moisture behind it on the 2x4 pine joists?  I live in Austin, and mold is a thing.*

Now, I'm considering insulation/interior walls...considering mold/cost/natural non-toxic materials.
I'm looking at rockwool--but to get it without the brown paper--means I'm buying it at r-30 for attics.  I'm still shopping around, but it seems harder to find (not in bulk).

I can source a local lime plaster for flooring, would this work for walls as well?  I don't want drywall as it molds.  Checking into forever board--mag oxide--but have read mixed reviews here and am guessing it's expensive.  

Also considering something like straw covered with something natural--but then fire hazards right?  What if I soaked the straw with borax?  Then used a wall covering like burlap, wood siding, or just cloth...how to make it less of a fire hazard....

The other consideration are rats--ugh--I need to seal up all cracks due to the tree rats, but will this mess with ventilation in the roof? I see the buildings he usually builds are built to breathe with large openings, and I'm wondering if I seal it up, it will trap moisture and cause problems....

Thinking I need to seal up and then insulate the metal roof for warmth in the winter time....in summer also...although I did have him install ventilation windows that can open to release the heat...it's super hot in there right now.

As far as climate control--I may do a box a/c or just a fan; winter could install a rocket stove when I figure out how to build one...lol...until then, hoping to get some insulation that is efficient, cost effective, and non toxic/doesn't mold.

Any thoughts/help appreciated.  Thanks!

Moisture is an issue of ventilation and leaking roofs.
tyvek barrier is a good product
Roof needs specific roof insulation- reflective and rockwool
Is the brown paper there simply to reduce itchiness
what plaster sheet works on a floor and a wall?
Drywall is only affected if its poorly designed, its made of gypsum in Australia
How big is this room

Hi Jennifer,
The size of the building would be good to know, as John asked. I also agree that the tyvek (while not natural) is not really a bad thing. I might not put it on, but I wouldn't bother to take it off, if it was already there.

For batt style insulation that is natural, I would look at the rockwool (like you mentioned) also there is hemp based insulation and sheep wool insulation which are also fairly natural. Some of the blown in cellulose insulation is made from recycled blue jeans and news papers which is certainly a step above fiberglass or spray foam.

Honestly though, as soon as you throw in rodents and mold, then I would suggest looking into hempcrete. It uses what is typically waste from the hemp fiber or oil industry and mixes with a lime based binder. It is not a structural material, you need to still have a frame up, but the hempcrete fills in between and beyond the studs to create a solid wall that is extremely hard for rodents to chew and is too alkaline to grow mold. This is a similar process to what many European buildings used hundreds of years ago. The outside and inside are finished with a lime based coating and that is your entire wall. No need to have 47 layers in a specific order, like modern building :)

Downsides are that it is difficult to get in the US, you do have to be careful with the lime until it is mixed with water, it does need to be protected from ground contact and precipitation or it will start dissolving and you will have to replace it. And you will probably get jokes about it being a "weed house".

**Edit - Hanging things inside the house is also more difficult, as you need to use masonry anchors instead of simply screwing into something like wood or sheetrock. Running plumbing and electrical can be more difficult as you cut or chisel out a channel, put in your pipe, and then cover over with more hempcrete.