Over months and years of exposure, your tile roof will collect dirt and grime. This can include anything from dust to tree sap to living annoyances such as moss and mildew. Moss and mildew can be particular problems, because they won't wash away easily and will spread with time. Fortunately, with the appropriate cleaning products you can clear the roof of all these problems at once.
Safety is the most important consideration when attempting to clean a tile roof. The most obvious consideration is the height. Be certain the ladder you use to reach your roof is placed on solid ground. For very high or steep roofs, a harness can be an important safety measure. Be aware that tile can be extremely slippery when wet, and are even more so when coated with mildew. Use boots that have good traction.
For the cleaning solution, mix one gallon of hot water with one cup of bleach, one-fourth of a cup of laundry detergent, and one-fourth of a cup of trisodium phosphate. Use a two-gallon bucket to mix the ingredients. Pour some of this cleaning solution into a sprayer bottle or the reservoir of a power washer. This cleaning solution is toxic, so wear eye protection and heavy, water-proof gloves when spraying. Consider tying garbage bags around your downspouts to protect your landscaping.
First, be certain you have enough hose length to reach your entire roof for rinsing. Then spray the solution onto your roof. It's important to thoroughly cover the roof, so refill your washer with more solution if necessary. Once you've sprayed the entire roof, go back and spray the worst spots again. Once the solution has soaked in for about half an hour, use a low-pressure spray washer or a hose with a brush to scrub your roof. Clean the worst areas, then move on to the rest of the roof. Always spray downhill on the roof to prevent the water from squirting underneath the tiles. Don't forget to rinse the gutters and downspouts, and remember to remove the garbage bags when you're done. When completed, your roof should be clean. Although you can clean your roof every season, it's generally not necessary to do it more than once every year or two. That's about how long it takes moss and mildew to start to regrow. Installation of copper strips can help prevent the growth of these types of organic matter.