So my attic is generally well insulated and the roof is well ventilated. Except there was a porch added on to the back portion of the house. This was then finished into a room and has since cut off all of the ventilation for that portion of the roof. Looking at the snow it is melting in this one portion of the roof (Since there is now inadequate ventilation) and then refreezing and damming at when it runs down onto the added on room. This is particularly disturbing because that room is a low pitch roof and I am afraid water is going to start backing up.
This section is also has a few recessed lights that I intend to insulate a little better and some dropped soffit in my kitchen, which I have to do a better job of sealing. However, there is nothing that I can do about the ventilation, there is a room in the way. I was thinking about attaching foam board to the actual roof. This should keep insulate the roof so that it keeps the snow frozen, at least in my mind.
When a shed roof abuts a wall you can install a wall vent and cut a slot in the decking at the roof wall junction to install the vent. Looks like a little box running the length of the wall, and of course has to be integrated into the siding with a large z flashing detail. 6/10 diy difficulty if well coached.
Or you could tear out the ceiling and spray foam the underside of the decking, which shouldn't be too outrageous in price for a small room, but is 10/10 difficulty diy (i.e. get out your wallet).