6" DuraVent DuraTech 8" 7-12/12 Adjustable Roof Flashing 6DT-F12L 8" 7-12/12 DuraVent DuraTech Adjustable Roof Flashing is used to weatherproof the penetration of chimney pipe through the roof. Storm Collar required. Made of galvalume. Available with large base. Diameter: 6" Pitch: 7 - 12/12 Vertical rise: 8" Galvalume construction 10â€-24†diameter pipes feature an .027†430 stainless steel inner wall and an outer wall of .029†galvalume or .027†430 stainless steel. A Refractory insulation is encased between walls. Only stainless pipes use the stainless end rings. Regular galvalume pipe uses galvalume end rings.