Flash and Batt but a little different take
After reading and watching everything I can on flash and batt (the good and bad), I still have one lingering question that no-one has addressed and I hope someone here can help.
Background… a gut remodel of an old, solid block home in zone 4A. Framing had to be offset from the block wall by 5″ (long story). So, we have a continuous masonry wall that will have 2 inches of closed cell foam, then about 2-3″ inches of empty space, then 2×4 walls. This is an urban environment, so noisy… and for sound attenuation as well as additional R value, we think we want to add 3.5″ Rockwool/stonewool friction fit batts.
2″ of continuous ccSF will provide a vapor barrier. Rockwool is vapor permeable. So does it matter where the Rockwool lands? Should it be pressed up against the foam (leaving a gap between it and the drywall)? Or should it just fill the 2×4 cavity and leave a gap between the foam? Thanks!
Replies
Your approach sounds interesting, especially with the goal of sound attenuation and added R-value. I’m curious, though—have you considered how the air gap between the closed cell foam and Rockwool might impact the overall thermal efficiency or soundproofing? Would it potentially create any issues with moisture or airflow?
Rockwool should fill the 2×4 cavity, leaving a gap between it and the ccSF for optimal insulation and sound attenuation.
Great question! In your setup, the placement of the Rockwool can impact both sound attenuation and thermal performance. Ideally, you should place the Rockwool directly against the 2 inches of closed cell foam, filling the 2x4 cavity completely. This arrangement minimizes any gaps that could reduce sound insulation and thermal resistance.
Ensure that the Rockwool doesn't compress the foam, as maintaining the integrity of both layers is crucial. The vapor permeability of Rockwool shouldn’t be an issue since the closed cell foam already serves as the vapor barrier. This setup should provide you with effective soundproofing and insulation.
Hope this helps with your remodel!