Ripped an old 70s fan out of our bathroom and what I thought was vented really wasn’t so this is becoming a larger job than expected. There was a rigid 3″ duct running from our old fan and resting inside this hole for a roof vent which was not proper.
We live in Washington so proper ventilation is important. The plywood on this side of the house around the old bathroom vent was black with mildew/mold prior to these pictures until i sprayed it with rmr86.
I got the fan in, now it’s time to tidy up the electrical & run ducting. My question is, should I drill an additional appropriate 4″ hole next to where it was previously venting or can/should i just use this larger (8″ish octagon shaped) hole and replace the roof cap with a dampered exhaust cap?
If i use this existing hole what should i use on the inside to properly secure the smaller ducting since it won’t be a snug fit?
Pictures include the outside cap, inside & a wider outside view showing the roof I’d be working on and where additional vents are located. TIA!