Roof cleaning is a great look for a home with old shingles. It doesn't hurt them at all. Many people think they need to be replaced when they look like this, but that is not true, The black is actually saprophitic fungus which eats away at the organic material your shingles are made of , It also holds heat and moisture in the house.I spray the way the shingles are laid so they don't pull up and no  water leaks in the attic. It removes all the mildew, mold and old dirt and makes it bright and beautiful. Most people just don't think about their roof, But the roof is a real improvement that is noticed immediately. Roofs start at $50 depending on how much saprophitic fungus and how large they are. It also depends on if it is metal, shingles or tiles. Call me out for a free estimate.