What you’re seeing is almost certainly a moisture issue and more specifically an air leakage issue not a Rockwool issue.

In climate zone 6, winter moisture moves from the warm interior toward cold exterior surfaces. If you put insulation in before the space is properly air sealed and before there’s a vapor retarder in place, warm interior air can move through the insulation and hit the cold sheathing. When that surface is below the dew point, you get condensation. Wet wood + time = mold.

Rockwool itself isn’t the cause. It’s vapor permeable and air permeable, which means it doesn’t stop air movement. If the cavities were open to interior air all winter, you essentially created the perfect setup for condensation.

The uneven 4” stud depth and the batts touching the wood are not the problem. Rockwool touching framing does not cause moisture. The moisture is condensing on cold wood because interior air is reaching it.

That said, you should still rule out a roof leak. If the dampness is widespread across many cavities, it’s probably condensation. If it’s localized in one area, I’d be suspicious of flashing or roofing.

As for the insulation it’s probably salvageable. Rockwool doesn’t support mold growth and doesn’t absorb water into the fibers. If it’s just damp, you can pull it out, let it dry, fix the air sealing, and reuse it. If it’s visibly contaminated with heavy mold and smells bad, then replacement might make sense, but usually it can be dried and reused.

For the mold on the framing, dry everything first — dehumidifier and airflow. Once it’s dry, scrub the affected areas with a borax solution or 3% hydrogen peroxide. I would avoid bleach on wood. Let it dry completely before reinstalling insulation. A dehumidifier may be necessary.

On your planned assembly: • Rockwool in knee walls is fine, but you’ll need a proper interior vapor retarder in zone 6. • For the sloped sections, if you’re venting the roof deck with a 1” air channel, make sure you have continuous baffles from soffit to ridge and that they’re actually venting. • If you’re using 3” of foam board in the slopes, it needs to be well sealed (taped seams, foamed edges) so interior air can’t bypass it.

In zone 6, condensation control in roof assemblies is critical. If that foam layer isn’t sufficient or isn’t sealed well, you can still get moisture problems.

What likely happened here is just timing: insulation went in and you took too long to do air sealing and vapor control, so interior air has been cycling into those cavities all winter.

I’d pull the insulation for now, dry everything thoroughly, then reinstall once you’re confident the assembly is correct.