Why are bituminous shingles only installed on bituminous mats and not directly on OSB-3?

It is important to know that, no matter how good the quality of the OSB, the Rar Acoperis team and the shingle manufacturers must install a bituminous mat on the OSB. This protects the OSB from water infiltration, mold, and discoloration of the bituminous shingles. When building the roof of your dreams, be prepared to choose the Rar Acoperis team.