The timing of this year’s International Home Show was convenient for me. I spent some time on the show floor talking to manufacturers about mineral wool insulation, sometimes called rock wool. This is a topic Fine Homebuilding will cover in an upcoming issue. It’s not a new insulation product, but it’s gaining popularity in the U.S. thanks to some distribution improvements from manufacturers like Roxul, CertainTeed, Thermafiber, and others.
If you ask me, it’s easier to cut, handle, and install into a frame cavity than fiberglass. Others will tout its waterproofness and fire resistance. But I knew all that before I set foot on the show floor. However, in interviewing fiberglass insulation manufacturers, I learned a few things that require further investigation. (If you want to play devil’s advocate on a product, just ask their competitors.)
The answer is that mineral wool boards are stronger and denser by necessity, not by design. When fiberglass is spun into a mat, the fibers are long and therefore easily bond to each other to form a cohesive mat. Mineral wool has much shorter fibers, so they must be packed more densely to keep the felt together.
I have been assured that there will be data to back this up, but I have heard that an independent study of the STC (sound transmission class) of glass wool and mineral wool has found that there is not much difference in performance between the two different materials. Again, I have not seen the report myself, but I wonder if this is again a density issue? In other words, were the testers evaluating the batting as we buy it, or were they playing fair in terms of density by testing the material itself without regard to retail density.
There is much more to this topic, but after a few conversations I had at the show, I am starting to think it will be broader than I initially thought. If anyone has any feedback on their experiences with fiberglass and mineral wool, please share!
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I just insulated my shop with mineral wool, and like Justin, I found it easier to install than fiberglass. I don’t care if the MW butts are stiffer than the FG, as long as they are. The hardness of the material makes it easy to handle and cut (I used our steak knife, and the serrated blade did a great job), but it can make it a little tricky to install into small cavities.
I would say MW is more irritating than FG, but the difference is not noticeable when I wear long sleeves, gloves and a mask. However, after taking off the mask, I soon started coughing. After I took off the gloves, there were fibers on my skin. I did not take off the long sleeves.
Would I use it again? Without hesitation. It is difficult to get a good installation with batt insulation and MW is the best installation I have ever done.
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