I had such a great experience with Roxul Comfortboard for my exterior insulation wrap that I decided to use another Roxul product to insulate my wall cavities. Roxul Comfortbatt has some of the same properties as the Comfortboard. It is fire resistant, sound absorbent, mildew resistant, and has a high R-value per inch. A 3.5" batt for a 2x4 wall is rated as R-15. That's 4.3 per inch! (Comfortboard is 4.6 per inch due to higher density.) A fiberglass batt is typically R-11 or R-13 and that is if it is installed correctly with the paper facing stapled to the studs and precise cutouts around wiring and boxes. Perfect install is difficult since the batts usually end up squished in places or have air gaps around penetrations. Fiberglass batts also sag over time. Plus it is extremely irritating to the skin.
Due to poor experiences with fiberglass, more people are turning to foam for insulation. While foam has a higher R-value per inch (R-4 to R-6) and is very rigid, it off gasses over time and looses some of it's R-value. The manufacturing process is also toxic to the environment and the foam is not recyclable.
Rock wool insulation is made from stone rock spun into fibers that create a rigid batt which friction fits into the stud cavity. You simply stick in the flexible edge of the batt with the W markings next to a stud and then press in the other side. You can easily make cuts for narrower cavities or boxes with a bread knife without compressing the batt. Long clothing, gloves and a mask are recommended for installation but I installed some of it in a T-shirt and was not bothered by the fibers.
I ordered the insulation online from Lowe's since they don't carry it in the store and it was less expensive than another distributor in town. I paid about $275 for 7 bags of insulation which covered all of my walls and ceiling. The Lowe's location is also convenient for pick up. I could have had it delivered to site for around $80 which is what I paid for the Comfortboard but that came from Tacoma, WA. I thought it would be more fun to pick it up with my Subaru too.
Some days I really want to have a truck to haul around materials and pick up things found on Craigslist. I will likely trade my Subaru in for a Toyota Tacoma in the next year but it really is fun to see what I can do with my Roo. And the looks on people's faces as I drive by is priceless ;)
It's been great to feel the difference the insulation has made inside the house! What most people don't realize is that insulation helps keep spaces cool as well as warm. With temps in the 80s and 90s lately, it was getting quite hot inside. Installing the metal roof helped reflect some of the sun's rays but the Roxul has kept the interior much cooler. Now my walls have an R-value of 21 (typically R-13 for a 2x4 wall) and my roof is R-25 (typically R-38 but it would be difficult getting it there in a tiny house without an attic). My extruded polystyrene floor has the highest R-value at 27.5 for 5 1/2". If I build again, I would use Roxul batts in the floor where I could get R-23 (typically R-30). But with a space this small, the insulation should be sufficient. (Can you tell I work in the energy efficiency field?)
