See if these help From the 2006 IRC: R102.1 General. Where, in any specific case, different sections of this code specify different materials, methods of construction or other requirements, the most restrictive shall govern. Where there is a conflict between a general requirement and a specific requirement, the specific requirement shall be applicable. R703.10.2 Horizontal lap siding. Lap siding shall be lapped a minimum of 1" inches (32 mm) and shall have the ends sealed with caulking, covered with an H-section joint cover, or located over a strip of flashing. Lap siding courses may be installed with the fastener heads exposed or concealed, according to approved manufacturer's' installation instructions. ( not exactly what you may be looking for; however, it does indicated per manufacture)