Here we are in Florida, algae grows everywhere. It is on your siding, your driveway, even your roof.
Basic maintenance should include at least a full house wash ever other year. Roof ever 4 to 5.
We focus on soft wash systems, while high pressure has its uses. Our soft wash is gentle enough for roof tiles but can still cut through dirt and grime that works into the cracks of stucco walls.
You may not even realize how bad it is, until it is gone and you can see your siding again for what it is.