The DuraTech 6" Class A Chimney Pipe Large Base Adjustable Roof Flashing for 0/12 - 6/12 Pitch Roof flashing is used to weather proof the penetration of chimney pipe through the roof. Storm Collar required. Select roof flashing based on pitch of roof. for example, a 6/12 pitch has a vertical rise of 6 over a horizontal distance of 12. Made of galvalume.