Thread: Black stains on asphalt roofs?

Hello,

Is this black staining comminly seen on lighter asphalt roofs algae? If so will this reduce the life of the shingle? How would you report on this?

Thank you have a great day!

Mike

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Without a picture, yes, there is a variety of algae that causes that black stain. I tell people what I think it is.
I believe it is harmless but it eventually leads to a buildup of organic material where moss can start to grow.

There is a one strain of the black streaking/staining that reportedly is living off the limestone in the roof granules. Some say the amount of limestone the stain is eating is not a problem and others take a hard line and say any deterioration is deterioration.

Those also report that there is more limestone in shingles than in the past to add weight to the shingle to prevent blowoff. As a result, the problem is more common.

The way I understand it is;
All roofs have it, white roofs show it.

Got a call from a buyer who's insurance company refused him a permanent policy until he had the "mold" removed from the roof. He wanted me to pay for it.

Told him first of all it's not mold, and 2nd, I ain't gonna pay for it!

Copper strips, to a lesser degree copper treatment on the shingles (usually on the granuals), work to inhibit the growth (oxides washing on area serve as algicide). Zinc strips are claimed to be somewhat effective. Organic material (even dust in the wind) and water (condensation) is enough to support it. If the composition shingles had copper treated granuals, then it is a sign that the shingles have deteriorated (lost granuals) somewhat or have some age on them. Not all are/were treated (cost more).

It is often called blue-green algae - appears black. Tends to show up more on shaded areas and exposures that don't get strong south and west sun or are slow to dry from frost/dew collections seasonally.

Sometimes dark streaks are incompatible/deteriorating metals reactions with what is below, for example dipped fasteners in cedar will corrode quickly and streak black.

Soot staining even from bar-b-Q or fire pit activity below can cause sticky streaking on the roof.

Photo and more details, instead of guessing would be nice.

I don't remember where I found this so take it for what its worth.

"Unsightly black stains or streaks on asphalt shingles are caused by a hardy type of algae called Gloeocapsa Magma."

I do know that zinc kills the black stuff I see on roofs here. I have seen roofs covered with it and clean strips down from any galvanized flashings or vents that were in the roof. Strips of zinc can be placed under the ridge cap shingles with exposed zinc to wash down the roof and kill the algae.

Originally Posted by Vern Heiler

"Unsightly black stains or streaks on asphalt shingles are caused by a hardy type of algae called Gloeocapsa Magma."

I do know that zinc kills the black stuff I see on roofs here. I have seen roofs covered with it and clean strips down from any galvanized flashings or vents that were in the roof. Strips of zinc can be placed under the ridge cap shingles with exposed zinc to wash down the roof and kill the algae.

Thanks, Vern. I dug up this pic of both, black streaks and a zinc strip.
The roof is over 10 years old and the zinc is starting to lose the battle.

Originally Posted by Vern Heiler

I don't remember where I found this so take it for what its worth.

"Unsightly black stains or streaks on asphalt shingles are caused by a hardy type of algae called Gloeocapsa Magma."

Here is one source for Vern's Gloeocapsa Magma.

The primary species of algae being observed is Gloeocapsa Magma.

Here is a recent Consumer Reports article (blog November 2009) on the remediation: Consumer Reports Home & Garden Blog: Tip of the Day: Get rid of roof algae, which can damage shingles

The Consumer Reports article says the algae causes damage. Has anyone seen damage to shingles from algae? I've seen the damage from lichen.

The Roofing Manufacturer's bulletin says to use a "latter" to access the roof!

Gary Sullivan seems to endorse Roof Reviver (sp) to clean the algae. Simply spray on, agitate and rinse or just let it sit and let the rain wash it off.. I have not tried it.

I have seen other sources (Inspect-A-Pedia) for one that describe some of these stains as being leaching of the asphalt in the shingle. The main difference between leaching and the algae was the pattern of the stain. Leaching appears to come from a point and spread outward, while algae has a wider spread pattern or covers a large area of the roof. The kick-off article appears here Asphalt Roof Shingle Home Page: Contractors, Claims, Diagnosis of Failures - How to recognize asphalt roof shingle failure types, black stains on roof shingles, thermal splitting and shingle cracking, and how to get shingle failure warranty and repai. If you refer to the article list on the left side of the screen, you will see a number of other articles related to staining and other roof maladies.

Thanks all for the good info!
mk