My Portland, Oregon 850 sq ft double wythe brick house with a flat roof (actual pitch is 1:30) and parapet wall that ranges from about 10″ at SW corner to 27″ at NE corner.  Putting down a new membrane roof on plywood decking after a seismic retrofit.  There are 16″ center 2×8 roof rafters and 2×8 ceiling joists, r38 fiberglass batt insulation, and will replace the existing 5 roof vents.

My question is, at the NE corner, due to roof slope, the roof rafters & ceiling joists overlap, limiting any potential air flow between bays.  I have been told I should drill vent holes through the rafters (above level of insulation), but have not been able to find any info on size & spacing of holes.  Any suggestions?  thanks!