Those dark stains aren't dirt — they're alive and eating your roof.

In November of 2011 I wrote a blog post about using zinc strips to prevent moss from growing on the roof, or possibly to kill moss. I conducted a fairly long-term experiment by installing zinc strips ...

Question: We are about to put our house on the market and would again value your advice. Our 15-year-old shingles have serious algae stains. I’ve read your advice and understand the cause and remedy.

Semi-Long Term Experiment Results: Zinc Strips Kill Moss on Roofs Not only does moss look terrible on roofs, it will also shorten the life of the roof covering and possibly lead to roof leaks.

Q My family room is attached to the house and has a two-slope gabled roof. Moss grows on one side, so much that it becomes thick and water-logged. Water backs up under the shingles and causes stains ...