What to do with mineral wool excess insulation?
Hello all,
I special ordered a bunch of Owens Corning mineral wool insulation that is 16″ x 47″ x 7″. I would say it is exactly the same as Roxull, however I am not for sure. I used it in my walls and now I have about 80 pieces of 16 inch wide x 47 inches tall by 7 inches thick left over. I also have probably 150 pieces from my wall studs that are 1.5″ thick shavings. I was originally going to fur out my walls 1.5 inches so the 7 inch thick piece of insulation would fit right in. However things changed and I did not end up doing that, the result is a bunch of leftover shavings.
I’m going to insulate my attic with R 38 fiberglass kraft faced insulation (one side). I am wondering if it would be wise to use my leftover mineral wool insulation on top of the fiberglass in the attic.
I’m considering my full pieces to be used either in the garage or the basement in the future when I have time to do those projects, while only using the 1.5″ pieces in the attic.
Any input would be greatly appreciated.
Thanks.
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Replies
Adding more insulation in the attic can only help, even if it's not done ideally.
I would gladly buy that from you if you truly have no use for it. I could use it in my aged home. Curious how much shipping would cost to Denver. I do agree with Charlie though, attic I insulation can be bumped up with your leftover product.
NICHOLAS - Could you please tell me how you cut the 1.5" pieces? Are they 7" thick? Were you able to cut them fairly uniformly? I am considering a project using 1.5" x 2" pieces on an interior 2x4 stud wall of a double stud wall, and using 5.5" in between the studs. Practical or pain in the ass?
Charlie- That is true 99% of the time. I suppose it is fine in my case, too. However I know it would be bad to add another type of insulation with it's own facing/vapor retarder as that would trap moisture in between the two barriers. Mineral wool is unfaced and to my knowledge is fine to mix with other types. I know I am putting on a vapor barrier out of Certainteed's Smart Membrain product that is applied similar to poly barriers with the one exception that this adapts to moisture from my research.
Peter - I feel this would not be possible to ship unfortunately. I am 4 hours from Denver. Per Charlie's suggestion and my previous idea I probably would use it up unless someone local wanted the product for a decent return on my cost. I can tell you it costs twice as much as other insulations.
KEVIN - I took a piece of 5/8" thick OSB and cut it to be 18" wide. I then placed a piece of mineral wool ontop and then marked each side. I then took my two stud depths (2 x 6's in my case) and fastened them to the OSB to make what I call a jig. This allowed me to just drop a piece of mineral wool (it's fairly rigid and holds shape) in between the two 2x6's. I then used a 12" long Serrated bread/steak knife. I work in a restaurant and was able to get a couple freebies that were dull but still cut this stuff. I had to make a sawing cut (back and forth) along each side of the mineral wool. I just rested the blade against the 2x6 edge and used that as my guide. I then would slowly peel the 1.5" thick layer back and sometimes used the knife to 'fillet' the mineral wool like skinning an animal. My pieces were not 100% uniform but I would say I have 80% of them that are just about 1.5" thick. some less some more. What is the third dimension of the pieces you are talking about? 1.5" x 2" x ? - When this is cut to 1.5" thick it's still fairly rigid and uniform. But when you cut it in little strips it is hard to work with because it loses strength.
I will say it was a bare to do. I solely regret not adding the 1.5" firring strips after I decided against it. For some reason I figured it would take a lot of time and extra cost to fir the walls out but I forgot all about the extra time I had involved with skinning each 7" thick piece. However, I know I have a quality product and that my extra pieces will be put to good use.
You can order the mineral wool from Owens Corning or Roxul in 2 or 3 thicknesses. 3.5" thick, 5.5" thick, and 7" thick.
Feel free to add detail of your plan or wall makeup and I can give you my experienced opinion after doing my whole house DIY with this.
Nicholas - Thanks. My strips would be 4' long, and cut to length as needed. They would be attached to 2x4's on their edge before standing up the wall. The 1.5" thickness would keep the 2x4 wall 1.5" away from the outside stud wall, then I would fill the space between the 2x4 studs with 5.5" roxul.The other options are to use 2" roxul board between the 2 stud walls (expensive) or 2" foam then 3.5" roxul in the stud cavities.I'd rather use all roxul batts if the skinny strips would hold up. So, inside to outside : gyp board,2x4 studs filled with 5.5"roxul, 1.5"roxul on stud and plate edges, 1/2 ply air barrier, 2x6 stud wall with 5.5"roxul, fiberboard sheathing, water barrier, rain screen, siding. Will the skinny strips hold up or drive me crazier than I already am?
The strips measuring 1.5" x 1.5" x 48" would be manageable but very time consuming. I know cutting 1.5" thick xps foam board will be slightly easier (just as messy) but it will be a rigid piece of foam versus a limp strip of mineral wool. I can't imagine the cost of foam board being too high for those narrow of pieces cut out of a 4x8 sheet. Perhaps another poster may have a second opinion. I would be on the fence between the two. You would have to absolutely nail or glue the strips to your wall before standing it up with either product. The foam would probably go on easier if you get a decent way to cut it.