I am new to this forum and wanted to give some back ground and introduction. I am the President and founder of Sullivan Roof Cleaning, Inc. We are located in the Greater Des Moines, Iowa area. Though we clean all types of roofs, we specialize in cedar shakes shingle roofs. We have cleaned hundreds through out Iowa and we also service Nebraska and Minnasota at present. We are expanding throughout the central midwest. We use what is called the soft wash process. Though I won't go into great detail about our process, I will say we do not use pressure, nor sodum percarbonate (disodium peroxydicabonate) or oxalic acid ( which is toxic) in our process, nor do we use the common roof mix. Though some still use the SP & OA, it is not effective at killing fungi. It also requires the use of pressure which is not recommended for cedar shakes, more so, old cedar shakes. Thus the soft wash process. Though cedar shakes over time, which is subjective, will gather the common infestation i.e. algae, moss, mold, mildew, lichen and fungi. There is also UV damage to consider. Of all the infestations, the fungi, what is called white rot fungi & brown rot fungi, will deteriorate cedar shakes and cause the most damage of all infestations. Most believe that all the brown or black discoloration of shakes is caused by tannins that leach out of the wood. To a degree that is true. All cedar shakes over time will loose their protective perservative and their cedar color. The brown to black color is also and in most cases more so brown rot fungi. Though the gray color can also be from UV damage, to a degree, when you see the light grey to white color that is white rot fungi. Though this may sound alarming just in the terms, it is a common infestation. These fungi’s do not have chlorophyll and cannot manufacture its own food. It feeds off of the cells in the wood. The fungus secretes enzymes that break down the wood or lignin, which is the substance that holds the wood cells together. Thus the light grey to white coloration and the brown to black coloration. Once these infestation are removed the shingles will return to their normal function and thus serve the purpose there were designed for, that is to protect the underlining felt. The felt protects the roof and the shingles protect the felt. Cedar shakes are organic and need to be maintained in order to reach their full lifespan, which can be anywhere from 40 to 60 years, which is subjective based on being maintained. I relate the cleaning process to having your teeth cleaned, which are also organic and need to be maintained in order to reach a full lifespan. The number one authoritory on cedar shakes shingles is the cedarbureau.org, though I do not use the same cleaning solution they recommend, as I developed my own. They are the authority. One thing you should never do with a cedar shake roof is seal it. It is wood and needs to breathe. Thus the gap between the shingles so they can contract and expand. They are not sealed when you buy them! The school is still out on staining them. If nothing else it can be added curb appeal, though pricey. There are 10 different grades of cedar shakes, not to be confused with cedar shingles, which are use mostly for siding. When considering a cedar shakes roof cleaning always know the grade of shakes, as the sloutions needs to be adjusted to gain the proper safe cleaning. One solution mix will not fit all. Given we have developed our own soft wash non pressure process and our own cleaning solution, that is not to say other forms of cleaning are not effective. From a cleaning stand point, our cleaning will last 5 to 8 years, which is also subjective based on roof environment. It will restore the integrity of the shakes, thus extending the lifespan and also will add curb appeal. For more of what we specialize in go to: www.cedarroofclean.com Here is a before & after picture of a job we just finished last Friday. No staining, no sealing, just a soft wash cleaning.