What is this stain on the roof?

Originally Posted By: lkage
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“I have never met a man so ignorant that I couldn’t learn something from him.”


Galileo Galilei

Originally Posted By: Jay Moge
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looks like maybe the start of a fungus of sorts. is that the North corner? icon_cool.gif


Originally Posted By: lkage
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Jay Moge wrote:
looks like maybe the start of a fungus of sorts. is that the North corner? ![icon_cool.gif](upload://oPnLkqdJc33Dyf2uA3TQwRkfhwd.gif)


No, it's the south east corner.


--
"I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei

Originally Posted By: Jay Moge
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maybe the bigining of the end for the shingles.


what about nails? maybe rust lines. ![icon_cool.gif](upload://oPnLkqdJc33Dyf2uA3TQwRkfhwd.gif)


Originally Posted By: lkage
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Okay I think I found the cause here:



algae and fungus

http://www.aok.org/roof.htm

http//:www.aok.org/roof/what-causes-stains.htm

http://www.askthebuilder.com/082_Black_Algae_Stains_On_Asphalt_Shingles.shtml


--
"I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei

Originally Posted By: escanlan
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Very interesting topic!! I have not encountered a roof with staining like this before but I do see a lot of it driving around outside of the Dallas area in the countryside. I’ve always wondered when driving by what was up with the roof.


Here are a couple more references to this:

http://bryophytes.science.oregonstate.edu/page9.htm
http://www.uaf.edu/coop-ext/publications/freepubs/HCM-04956.html

Now I have a question maybe someone can answer. The references discuss killing it with copper and zinc. One reference mentions placing copper and/or zinc strips under the shingles, leaving a small edge exposed. Over time and with rain, dew, etc. the copper or zinc strips will add the amount needed and flow down the roof killing the algae. Rolled copper for flashing use is readily available, although expensive. But due to the issues associated with lead and zinc I have not come across anyone that supplies these in a form suitable for flashing nor just as strips for this application.

In the absence of any algae stains on the roof or water penetration signs inside or out, is there any way to determine if the strips we see inserted under shingles are made of zinc? Copper is naturally easily identifiable. There was a discussion thread awhile ago about strips being found under shingles as a method of roof repair
( http://www.nachi.org/bbsystem/viewtopic.php?t=14254&highlight= ). Since I do see this type of staining around our area I would be interested in being sure what the strips are when making a call. Naturally the call would be "Consult a qualified roofer" but it would be good to know.


--
Manny (Emmanuel) Scanlan

Knowledge is power, but sharing knowledge brings peace!

Originally Posted By: jhagarty
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I see this type of staining quite often. The staining can be chemically cleaned from the roof surface.


Here is a link to a company in my area that Clients of mine have used. Link gives Before and After photos of the roof.

http://www.accubright.com/samples_res.htm

Accubright Systems, LLC
91 Newport Pike, Suite 303 - Gap, PA 17527-9579
Phone: 717.442.8939 - info@accubright.com


--
Joseph Hagarty

HouseMaster / Main Line, PA
joseph.hagarty@housemaster.com
www.householdinspector.com

Phone: 610-399-9864
Fax : 610-399-9865

HouseMaster. Home inspections. Done right.

Originally Posted By: lkage
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escanlan wrote:
Very interesting topic!!

In the absence of any algae stains on the roof or water penetration signs inside or out, is there any way to determine if the strips we see inserted under shingles are made of zinc?


Manny, thanks for the links. I agree...very interesting topic.

From what I understand it's not possible to tell if steel is coated with zinc just by looking at it. The metal can be chemically tested but that defeats the visual inspection part of the equation.


--
"I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei