GAF's California open-valley detail has product, slope and warranty limitations. Metal valley flashing and fastener placement must follow the complete detail.
GAF technical bulletin: California valleys open.
What this means for your roof
GAF’s California open-valley detail has product, slope and warranty limitations. Metal valley flashing and fastener placement must follow the complete detail.
A useful question for your contractor
Ask whether the proposed method is compatible with your chosen warranty.
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: February 1, 2021. This is the date of the manufacturer source, not a claim that this website guide existed on that date.
Read GAF: California valleys open
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.