Architectural Details: Flashings and Copings - Valleys
The shingles or slate must lap the flashing at least 6". Download CAD File. 9.5B. Equal Slopes - Unequal Water Flow. Where unequal water flow is expected, a baffle, 1-1/2" high, should be installed as shown to prevent water of higher velocity from forcing its way past the opposite edge of the valley flashing.