Metal roof cleaning, if done properly, can make your roof last a lifetime. Metal roofs are often victims to rust and other degradation, thanks to long term stresses from exposure to wind, rain, and sun. A metal roof can make your house look great when it's new, but in the long run it can be an eyesore if not well maintained.
One way to keep your roof looking good is painting it—this will keep the resale value up, make the roof look good, and even protect it from some damage such as rust and mold. If you're going to paint, the first step is assessing the situation and cleaning the panels.
Step 1 - Look at Damage on the Roof
Take a good long look at your roof to see what needs to be cleaned. Rust spots are a big factor here—it’s best to just get rid of them right away so they don't evolve, resulting in the need to replace the entire roof. Any debris should be pushed off. Bird waste, squirrel waste, branches, and anything else that doesn't belong on a roof needs to be dealt with.
Step 2 - Ensure Safety
While looking at the major areas that need cleaning, be careful about where you stand. Either set up a scaffold, or test each spot carefully as you go, to minimize risk.
Step 3 - Cleaning the Roof
A good, effective cleaning chemical is Tri-Sodium Phosphate, which should always be heavily diluted with water for safety. It can clean any grime and mildew from your roof ease. This hand-scrubbing method will take a long time if you do the whole roof, but it's one of the most thorough approaches you can take.
Step 4 - Spraying Down the Roof
About an hour after you finish the TSP application, spray down the roof with a high pressure hose to make sure it's thoroughly cleaned. Start at the top so the debris slides down with the water and falls off of the house. If regular water isn't cutting it, you can add some safe detergents to the high pressure hose to get some extra shiny oomf.
Step 5 - Finishing Up
Once the rust spots are gone, paint or treat the areas where they were to keep them from coming back.