Venting an attic in a mixed-humid climate – GreenBuildingAdvisor

I’ve watched a bunch of Joe Lstiburek’s lectures on attics and roofs and he always had said that a traditionally vented attic with an air tight ceiling plane and insulation on the attic floor was a safe method that works in every climate zone. Now I’m reading his moisture control handbook where he has an entire section on how venting an attic can actually do more harm than good if the air coming in is more humid than the air in your attic, especially in heating season why the roof deck is cool. He also references that the roof deck can be about 10 degrees colder in the winter as it looses heat to the night sky and then the air entering the soffits can condense on the decking. I always thought that ventilated decking was critical in a cold climate for preventing ice cams. I’m in a climate zone 4A in NJ so hot humid summers and cold winters. I was going to try for a vented over roof but didn’t know if my 100 year old 2×4 rafters could withstand 2 layers of roof decking and didn’t want to bring in a structural engineer (plus it was over double the price) so we decided to stick with traditional soffit and ridge. But after reading what he wrote, I’m second guessing myself, any thoughts on this? Almost everyone in my areas has vented attics.