Right brush, fungicide for moss on shingles

Q. For many years I've been scraping moss off an asphalt-shingle roof. Pine and oak trees flutter their needles and leaves all over the roof as well as shade it, obviously encouraging the moss. Does moss shorten the life of the shingles? Is it protection for the roofing? Is it a waste of time to remove the moss? Does the wire-brushing hurt the shingles? I cannot see any apparent effect. B. R. Farrand Willowdale, Ontario

A. It may well be that wire-brushing the moss is worse than the moss itself, since the surface of the composition shingles could be damaged by the wire. I'd prefer a bristle brush or blunt scraper to a brush made of wire.

There are commercial moss removers, such as Dowicide-G by Dow Chemical Company, Santo Brite by Monsanto, and Roof Cleaner by Sherwin Williams. Follow the directions on the label.

A home-made fungicide can be made by using mineral spirits mixed with 10 percent pentachlorophenol. Apply it in liberal quantities to the moss.

Does the moss have any deleterious effect on asphalt shingles in a cool, damp climate such as Ontario? I'd ask a local roofer.