Ventilation in a vaulted ceiling attic – GreenBuildingAdvisor

Hi all, 

I’d just like to sanity check whats going on in my vaulted cieling attic space. Fairly new to this but have been reading as much as I can on here and a little worried about ventilation in this part of the attic. 

I’m in the process of reinsulating my attic. There are two upstairs rooms with vaulted ceilings, framed by a fully closed-off knee wall on the attic side. Right now, there is faced r19 fiberglass. My plan is to replace those with unfaced r15 rockwool and then cover with 1.5in polyiso board and air seal around it with expanded foam. 

I’ve had to replace the LEDs in that room and saw evidence of fiberglass insulation between the ceiling sheetrock and the roof sheathing. The space appears to be vented by soffit vents at the eaves; however, the only exhast ventilation in my attic is a powered attic fan in the main attic area outside of the knee wall space (which i dont every power on after reading on here)

I’m not currently seeing any mold or moisture issues. Just want to make sure I’m fixing one problem and creating another one.

 

I’m wondering:

1. Given that the vaulted ceiling has no exhast ventilation, will airsealing the knee walls on the attic side with foam board increase risk of issue since it’s likely getting some drying from the “leakieness” of the current set up?

2. Should I potentially cut holes in each rafter bat at the top of the knee wall space so it can exhaust into the main attic space?

Here are pictures and a quick video of the space

https://imgur.com/a/3nVIJ6S