Should I install radiant-barrier insulation in a walk-up attic roof in Pennsylvania?
I have the same situation in Pa but have also tried radiant barrier with the ventilation holes. I am still in a quandry about how to use it. This is what I have experienced: I laid the foil over my insulation as often recommended. In the spring I went into the attic to check on the nature of things. I lifted a section and my fiberglass insulation was short of sopping wet! It took me short time to yank it all off of the fiberglass for it to dry out. 

I have concluded that I am not able to put down radiant barrier as I most likely have airs leakage through the ceiling causing heat to meet the cold. I do have an attic fan and could put baffles in for even better ventilation.

I am left with this last attempt to achieve at least some temporary benefit before the big redo: I am tracking the sun and will staple foil in a strategic spot on the attic rafters. The spot that is potentially hot in the summer (in my case the NW corner) but receives little warmth in the winter because of daylight hours. This should help the summer AC.  I am not ready to yank out all my insulation and look for leaks. One step toward betterment at a time.

I keep wanting to believe radiant barrier is wonderful but people with season changes better do their insulation/ventilation/air leakage homework before they think radiant barrier is going to be the best thing since sliced bread!