A composite roofing board is provided, including a layer of bituminous core material having pieces or particles of shingles, rolled roofing, etc. that have been broken-up or comminuted therein, with the core material having layers of mat material on opposite surfaces thereof, also in layers, and with an adhesive applied to an outer surface of one of the layers of mat material, with a peelable and removable release liner layer covering the adhesive. The various layers are provided as a sandwich, to make the composite board. A plurality of composite boards may be applied to a roof deck or other roof structure, and they can be butt-joined and taped together with a joint tape. The method of making the composite board can be continuous.