I got a flyer in my mailbox advertising a roof cleaning service. I'm not sure of the cost-- "10% off." (Uh, okay.) But it says, "The black staining on this roof (with photo) is not dirt be a harmful form of algae called Magma Gleocapsma. It feeds on the limestone filler of asphalt shingles. Left unchecked this... will reduce the roof's useful life."

Is this bullshit? Has anyone here had their roof professionally cleaned? What is a fair price?

I just bought a concentrate from Home Depot (less than $50) and sprayed it on myself.

A roofing buddy told me that copper flashing under the ridge vent will prevent the problem in the first place, so the next time I re-shingle this house I will probably do that.

The only issue I have here are the sections facing north.

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I got a flyer in my mailbox advertising a roof cleaning service

Yeah flyer in your mailbox is a clue. It is a ripoff. If this is done improperly can cause all kinds of problems.

I have never heard of cleaning shingles, ever. I also don't think that it's harmful if they're discolored. Now, if it's directly under a very thick tree and has algae from staying wet, this may be different. We clean tile roofs, but that's strictly an esthetics thing.

If you have or plan to have aluminum gutters, you do NOT want copper flashing it will eat holes in the gutters from galvanic corrosion and you need to use copper gutters at $28 per foot if you have copper flashing on your roof.

I think the discoloration is mostly a cosmetic issue, not safety.

Mildew etc. growing on shingles most likely does hasten their deterioration, but not by much I bet. Some people really find it bothersome and have it cleaned. I expect the cleaning would be as bad for the roof as doing nothing.

Galvanized flashing, like you see around many vent pipes, sheds trace amounts of zinc and kill it as well, like copper will.

I extremely rarely buy services from unsolicited sales / promotions.
If you have a trusted roofer and are concerned I would ask them.

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Originally posted by 220-9er:
I think the discoloration is mostly a cosmetic issue, not safety.

^This

I bought and used the stuff from HD. It takes a few months to work, but it works.

North side of my house is shady to boot so I had the dark streaks start in about year 10 of a new roof. Now it's year 17 and they are very noticeable on the lower half of n side roof. S side is sunny and still looks very good.

One of the sponsers of Reds baseball is an old line Cincy roofer and they advertise a shingle cleaning service pretty heavily. Say it's mold, not dirt. If I ever cleaned them I'd use a mix of about 4 parts water to 1 part bleach and add a couple squirts of dawn. Put it on wet roof w pump sprayer, agitate with a bristle brush or broom. Rinse with a garden hose with spray nozzle. Some use a pressure washer but I'd try hose with a spray nozzle first. No sense needless washing away roof granules.

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If you have or plan to have aluminum gutters, you do NOT want copper flashing it will eat holes in the gutters from galvanic corrosion and you need to use copper gutters at $28 per foot if you have copper flashing on your roof.

YEP.

The Asphalt Roofing Manufactures Association says that both algae and moss can grow on rootops, and that algae is not harmful but moss can cause problems. Link

Here's a link to homeadvisor.com which shows the national average price range, and you can input yor zipcode and get the prices range in your area. Link

We use these on customers roofs, who have moss or algae issues.

I recommend them, install once, permanent solution.

Lots of good info. Thanks to all.