Algae, mold, lichen, and bacteria don't just sit on the surface of your roof and siding — they work their way into materials, breaking down shingles, paint, and wood over time in a way that shortens the lifespan of your entire exterior. Standard pressure washing on a roof can strip granules from shingles, void warranties, and cause leaks, which is why the method matters just as much as the result. Ignoring the problem entirely, however, only accelerates the damage and leads to far more expensive repairs down the road.