So your roofer is trying to sell you venting, what makes you think you
need more venting? Do you have mold growing on the wood, is the
insulation moldy. and not from roof leaks, because if you dont have
moisture problems visable your Gable vents have been doing their
designed job, venting. My Gable vents have kept my roof beams and attic
fine for 110 years.