Your unprotected cedar shake roof is being attacked by a number of different sources. Some of these are tree sap, bird droppings, mildew, mold, algae, moss, lichen growth, and surface decomposition by sunlight and moisture. By removing these sources through cleaning with a specially formulated cleaning solution and then sealing/staining the roof with an algae and moss resistant sealer, you will extend the life of your expensive cedar roof.