My first post, so here goes. I have a an A-frame type house, but with curved sides. I'm in western Oregon with lots of rain and things wanting to grow on my cedar shingle roof. The current roof is cedar shingles, over roofing felt, over 1x4 horizontal purlins, over ridged insulation fastened to 2x6 T&G cedar which also forms the interior walls. No attic space. I have not had condensation problems I'm aware of. Because of the high maintenance required and difficulty doing maintenance on the cedar roof, I want to replace it with premium asphalt (CertainTeed Presidential). Two roofers both point out the ventilation problem with putting plywood over the purlins because of the air space created between the plywood and the insulation. Both say this would create condensation. One roofer says that removing the purlins and fastening the plywood directly over the insulation would eliminate the air space and, therefore, any condensation risk. The other roofer disagrees saying that the only satisfactory covering for this roof is cedar shingles that breathe. I would rather have the asphalt, but don't want condensation and mold as a result of an expensive mistake. I really need some sound, professional advice from people with experience. Thanks very much.