A common issue when re-roofing.. improper attic ventilation. Ridge vent should be installed ONLY on the highest ridgeline (unless the sttic is physically divided inside. By removing the lower installed ridge vents, this allows the proper ride vent to draw ONLY from the soffit intake vents, thus bringing cooler air into the attic and prolonging the life of the shingles, as well as limiting the amount of humidity held within the attic- thus reducing the viability of mold growth.