When leaves, twigs, branches, pigeon droppings, sand, silt, and other debris collect in the valley of a roof, proper water runoff is inhibited. During heavy rains, debris in the valley causes the water to damn and back up under the roof material. The water leaks onto the felt and wood below the roofing material, causing leaks and dry rot. The photos below show examples of debris that has collected in the roof valley.
Proper roof maintenance requires lifting the shingles or tile along the valley, cleaning all the debris, and then reinstalling the shingles or tile. If periodic roof maintenance was not performed and the debris in the valley has resulted in dry rot, then the field shingles or tile above the affected felt and wood must also be lifted, the damaged wood and felt must be replaced, and then the shingles or tile are reinstalled.
