I built a 30' x 50' shop with exposed rafter tails with NO possible access thru the soffit area for ventilation. I have started to have moisture problems on the ceiling and in the attic so I am installing Core-A-Vents product called In Vent on the roof about 30" up from the dripedge. This is really a hassle and it was stupid on my part not to provide ventilation to the attic or rafter bays when I first built it. Let me tell you more about its construction. The rafters are 2 X 8's and it is a tray ceiling with ceiling joists starting about 6' in from the outside wall. I used 6" insulation so there is a 2" air space on the top side of the insulation. It is also a hip roof. I am installing the In Vent on all 4 sides of the roof. My question is whether to use ridge vent or a power vent as the means of expelling the moist air out off the building. The ridge is only about 20' long because it is a hip roof.