Should I call for rigid mineral wool sheathing to be installed in two layers?
I’m planning to use rigid mineral wool sheathing on a retrofit project. In the past when I’ve done this with XPS or polyiso rigid foam sheathing, I’ve called for 2 layers of foam, with staggered seams, presumably because rigid foam shrinks and installing in 2 layers reduces the likelihood of “cold lines” in the continuous insulation layer. Mineral wood doesn’t appear to be a product that shrinks and the photos I see suggest that the product can be joined at each edge quite tightly.
The overall assembly planned is like this: new engineered lap siding over 1 x 4 furring strips anchored through insulating sheathing to the stud wall. Stud wall has 7/16″ plywood sheathing; all joints will be taped/sealed to create air barrier. Water resistive barrier will go over insulated sheathing, so it can be tied to the window and door flashings.
So, 2 layers of 1 1/2″ with staggered seams, or 1 layer of 3″ insulation?
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