Can Rockwool batts be pushed up against screws and nails?
Sorry for an obvious sounding question, but I’ve only worked with FG batts and can’t find an authoritative answer for this when it comes to Rockwool ComfortBatts.
I’m planning a new build and thinking about some of the details like penetrations through sheathing, in my case ranging from 1/2″ past the sheathing on the wall and 2″ past the sheathing on the roof. The roof one especially is large due to 7″ screws through 2 layers of polyiso.
I think the simple answer is that in new construction, you screw into framing so it does not present an issue. Yes, on the roof, that means being very careful about your chalk lines 😅
So my question is more about what happens in the cases where you have significant fastener / nail penetrations protruding (for whatever reason) and need to install Rockwool into the cavities. Will it conform? Will it degrade the insulation? Will it cause it not to fit tight against the assembly?
A good example is in a retrofit where my garage has massive nails protruding from the wall cavities, or my basement joist cavities.
For FG batts, I can easily understand how it just fits around any protrusions. But having never worked with Rockwool ComfortBatts and understanding it’s more rigid, that’s why I’m curious.
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Replies
Mineral wool batts can be installed just like fiberglass batts in this case. The fasteners (nails, etc.) will just poke into the mineral wool batts the same way they would if you used fiberglass batts. I doubt you'd even notice any difference while installing the batts.
For larger things, like oddball chunks of framing, mineral wool is NOT as comformable as fiberglass. You need to "notch" the batt and cut it to fit around those things. I use a wavy bread knife (I have linked to the one I use in other threads here on GBA), and it makes it very easy to cut the batts. You can use that same bread knife to split the batt when you have to go around wiring too.
I find mineral wool batts are actually easier to install than fiberglass, because it takes much less finesse to "fluff" mineral wool batts -- mineral wool tends to just mostly fit all by itself, so you just need to persuade it a bit at the edges to get a good fill. Fiberglass has a much higher tendendency to compress more than you want and to leave voids, so you have to be much more careful when putting a fiberglass batt into a cavity.
Bill
Kamranicus,
Like Bill, I find mineral wool batts easier to fit onto protrusions. Their greater stiffness allows fasteners to push through them, not just compress the way fiberglass batts can sometimes do.
Fantastic, thank you both!