"Joan Crowe, technical services director for the National Roofing Contractors Association, which takes no position on whether roof cleaning is necessary" LMAO Of course she takes no position. She represents companies that replace roofs.
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Elephant Roof and Exterior Cleaning Raleigh North Carolina David Hoover 919-207-0666 Benson NC. Roof Cleaning Raleigh NC
Both of the businesses referenced are the local "roof shampoo" guys around here. Consider the source. This "article" was actually published in the monthly Angie's list rag that members get back in the spring. If you're not a member, it's definitely worth it to join. If you're not sure why I say that, PM me for the reason.
NRCA won't take a stance, but GAF clearly makes statements about lichen and moss. I quote from it all the time, citing the reference of course.
“My roof is in the shade much of the day and it has significant areas of black discoloration that I suspect are mildew or something similar. Is having my roof cleaned necessary? Is it safe for the roof?” — Dora Garrett
Whether it needs to be cleaned depends on the kind of roof it is, according to Kelly Carter, owner of Window Gang, which offers roof cleaning in San Antonio. “Asphalt shingles can be damaged by [the discoloration] if it’s not washed,” he says.
The discoloration is caused by fungus and moss that feed on the limestone contained in asphalt shingles, says Karen Warren, office manager at AAA-1 Roof Care in Woodinville, Wash. She says the problem is complicated by especially rainy climates, like the Pacific Northwest.
“It rains so much here, so shadowed roofs don’t dry out and these organisms begin to grow,” she says.
Bob Clem, owner of Home Team in Maple Valley, Wash., says the best way to remove the moss from your roof is by applying a solution that kills the organism and its roots. “If it’s done properly, the roof won’t need to be cleaned again for six to nine years,” he says.
Most homeowners choose to clean their roofs for aesthetic reasons, says Joan Crowe, technical services director for the National Roofing Contractors Association, which takes no position on whether roof cleaning is necessary. Crowe recommends using a mild bleach-water solution with a soft brush or sponge. She advises against using pressure washers, which can damage shingles.
"The long-term effect is it will lead to moss, and moss is damaging. So if you get rid of the algae, you're not going to have that moss problem," says Mike Hilborn owner of Roof-to-Deck Restoration in Menomonee Falls, Wis.
Hilborn says cleaning a roof costs $400 on average, depending on roof size and pitch.
Roof cleaning questions answered by D.C. area experts Date Published: July 01 2011 Share
My roof is in the shade much of the day, and it has areas of discoloration that I suspect may be mildew or something similar. Is roof cleaning necessary? Is it safe for the roof? - Angie's List member Dora Garrett
The discoloration comes from algae, says Paulo Baesse, owner of highly rated Roof Real Clean in Falls Church, Va. "Curb appeal is important, but the biggest thing is the damage it does to a roof," he says. "You have a living organism eating your shingles."
Joan Crowe, technical services director for the National Roofing Contractors Association, which takes no position on whether roof cleaning is necessary, says discoloration is usually a problem that affects asphalt shingles. "You can clean it, but the discoloration will come back," she says.
Most homeowners choose to clean their roofs for aesthetic reasons, Crowe says. She recommends using a mild bleach-water solution with a soft brush or sponge but advises against using pressure washers, which can damage shingles.
Victor Fedoseyev, owner of highly rated Roof Clean Bright in Rockville, Md., says shingle manufacturers offer products treated with copper or zinc to inhibit algae growth, but their effect wears down over time. His company uses a mild cleaner with a low-pressure wash to clean discolored roofs.
Baesse says his non-chlorine cleaner and low-pressure wash typically prevents algae growth for several years. He estimates the average cleaning costs $350 to $795, depending on the roof's size, pitch and height.