What can I apply to asphalt shingles to stop moss from growing? I have tried everything from bleach, lime, and commercial moss and mildew killer. Nothing helps.
Shingle Shield Zinc Strips interrupt the flow of rain and naturally time release invisible fungistatic compounds of zinc oxide which travel down the roof slope. These compounds are absorbed by the roof surface and inhibit the growth of fungus, moss, and algae. When you see the Call to Order button next to a product in the Wimsatt catalog, that means that it is not available for order online.
Zinc Strips kill moss. The moss dies and the roof stays moss free for 10 feet under a zinc strip for five years or so if it stays in place and stays flat. Homeowners can install strips of zinc, purchased at a hardware store.
Jim had an interesting problem with his mother-in-law's house. The 25 year old roof had no moss, ever. Then he re-shingled and the north and east sides have been constantly covered in moss. Why and what to do about it?
This Old House replies: The black mold-like stains and streaks that appear on roofs, particularly light-colored asphalt shingles, is actually a blue-green algae Gloeocapsa magma. Commonly found in climates with warm, humid summers, it does no damage to the roofing, but it certainly does looks bad. You could replace all the roofing with new shingles dark enough to disguise the staining, or with shingles laced with copper granules, which are lethal to algae.
For decades, zinc strips have been used to keep moss from growing on roofs. This is an explanation of how they work and how they are installed. It also explains the limitations of zinc strip, from the point of view of good roofing practices and experience.
Shingle Shield should be installed in a straight line under the first row of shingles below the ridge. Beginning from either end of the roof peak install a continuous single row under the first available course of shingles below the ridge line. Slide Shingle Shield up under the shingle until its built-in alignment guide butts against the edge of the shingle.
Much to the dismay of homeowners, they provide fertile ground for a particular species of algae. Problem is, as they proliferate, the algae leave brown or black streaks on rooftops that can be a real eyesore. The algae develop under sustained humid conditions—for example, on rooftops that are seldom or never exposed to sunshine, or that are on houses surrounded by large trees.