/diy/ - Do It Yourself

Ill be using 2 x 6 wall studs 16" on center, exterior wall will be 1/2" plywood, interior wall will be either plywood, wood tongue and groove planks, or just plain planks. No vapor barrier or moisture barrier. Will be in the Tennessee (Sub-Tropical, but still has winter weather with below freezing). There wont be any wiring in the walls (its an offgrid cabin) and wont be any AC.

I want to use a natural and cheap insulation material, I do not want to use modern insulation (fiberglass). Id like to use sawdust (mixed with lime or borax "anti mold/insect") which I could pack in to the wall cavities as I build up the wall. This will get tricky when I get to the "fire blocks" in the stud framing. If I am using plywood for the interior wall, I would nail in the plywood, pour in the sawdust mix, pack it down until its level, and so on. I will be packing it down otherwise it will eventually settle leaving air gaps. However, sawdust can cause headaches later on if I wanted to get in the wall or inspect or modify, etc, especially if the wall is a 4 x 8' plywood, taking that piece off the wall will make a giant mountain of sawdust inside your house. I considered using some sort of cardboard bag like a leaf bag and fill that up with sawdust, tape the top, then pack it in to the wall cavities, but I am unsure on the practicality of this - not to mention insulating the ceiling rafters (45 degree angle).

Another consideration is tightly packing straw in the wall cavities, this has the benefit of not pouring out like sand as sawdust would. I powder the straw with lime/borax, build a portion of the wall, then pack the straw in to the cavity, and so fourth.

A last consideration is some sort of clay/straw "wattle & daub" type mix which will harden or some sort of "dustctrete" which is sawdust mixed with concrete. It will have to be lime mortar and not portland cement, portland does not breathe, retains moisture and will rot wood its in contact with (the wall studs).