Roof valley flashing including expansion joint

A roof valley flashing including a unitary strip of durable material adapted to be located in a junction between two plane surfaces of a roof, each said surface being covered with roofing material;

• said strip comprising a rectangular panel of polypropylenesynthetic rubber having a flexure section including at least one longitudinal fold through its center and laterally extending sides of such width that they can extend a substantial distance under said roofing material, each of said laterally extending sides including a group of longitudinally extending ribs spaced from and parallel to said fold, and interlocking ridges extending longitudinally between said flexure section and said groups of ribs, each said interlocking ridge including two upstanding sides and a top surface generally parallel with the surface of said panel with said sides angled outwardly such that said top surface is wider than the base of said ridge;
• each of said fold, said ridges and said longitudinally extending ribs being open at one end of said panel, and wherein a short section of said panel on the opposite end thereof is formed with at least said ridges slightly narrower than the ridges on the larger part of said panel.