Yes they do, and so do bare tiles, and so do replacement tiles and full new roofs, nothing will stop this process from happening.
But guess what, your roof can be kept clean without the need for pressure washing it repeatedly, in fact whenever it requires it, and if done before it gets too bad it doesn’t even need to cost a lot!
Where the roof has been coated previously it can be even cheaper to clean up, like your car (which also uses a coating to protect the metal) you can simply wash it down, no high pressure wash required.
Posted in: Roof cleaning
