Owens Corning requires a suitable valley liner and specified laps with the surrounding underlayment. It does not recommend weaving underlayment through a valley because trapped air and bridging can lift the shingles
Owens Corning technical bulletin: Underlayment Application in Valleys Technical Bulletin.
What this means for your roof
Owens Corning requires a suitable valley liner and specified laps with the surrounding underlayment. It does not recommend weaving underlayment through a valley because trapped air and bridging can lift the shingles. Installation-related buckling is distinct from a shingle manufacturing defect.
A useful question for your contractor
Ask for photographs of the valley liner and field-underlayment laps before they are covered.
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 dated: August 2023. The date shown identifies the manufacturer document used for this summary.
Read Owens Corning: Underlayment Application in Valleys Technical Bulletin
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.