... board sheathing , studs 3.24 0.31 3 / 4 - inch drop siding , 25 / 32 - inch insulating board sheathing , studs 4.09 ... add 0.98 to resistance in " " R " column CONSTRUCTION R U Roofing , 1 - inch boards , rafters 1.91 0.52 Roofing , 1 - inch ...