Flashings are used to seal the opening where the chimney penetrates the roof and to divert rain and snow down from the roof and away from the chimney system.A series of adjustable flashings are available depending on your roof pitch. A flat and low pitch flashing is used to seal flat and low pitch roof (up to 2/12 pitch) openings. To determine your roof pitch, measure the number of inches from the end of a level ruler down to the roof. This is the rise for 12 in of run. A rise of 5 in is a 5/12 pitch. 4 in, a 4/12 pitch and more.