Roof-to-wall joints, valleys and penetrations need correctly sized, integrated flashing. GAF describes how step flashing and counterflashing work together and why details must fit the selected shingle.
GAF technical bulletin: Proper flashing.
What this means for your roof
Roof-to-wall joints, valleys and penetrations need correctly sized, integrated flashing. GAF describes how step flashing and counterflashing work together and why details must fit the selected shingle.
A useful question for your contractor
Ask which flashing will be replaced and how the new water path will connect to existing walls.
Ask for the answer to be tied to the actual roof condition and the exact product being installed. Keep the agreed repair or installation detail with your estimate and project photos.
Bulletin revision: March 22, 2021. This is the date of the manufacturer source, not a claim that this website guide existed on that date.
This homeowner summary explains the cited bulletin. The complete manufacturer document and current product instructions govern the installation details. A requirement for one manufacturer or product should not be transferred to another without checking.