A composite insulated roof board structure comprising: (a) an insulated roof board member comprising (1) a main portion of rigid coherent solid insulating material, and (2) a top portion comprising a plurality of spaced blocks above said main portion and integral therewith, said blocks defining therebetween a network of interconnected channels at the same level for horizontal venting of water vapor; and (b) a relatively hard, dense protective top layer which is adhered to the tops of the blocks of said insulated roof board member. view more